What is SQL?

• SQL stands for Structured Query Language
• SQL lets you access and manipulate databases
• SQL is an ANSI (American National Standards Institute) standard

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What Can SQL do?

• SQL can execute queries against a database
• SQL can retrieve data from a database
• SQL can insert records in a database
• SQL can update records in a database
• SQL can delete records from a database
• SQL can create new databases
• SQL can create new tables in a database
• SQL can create stored procedures in a database
• SQL can create views in a database
• SQL can set permissions on tables, procedures, and views

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SQL is a Standard - BUT....

Although SQL is an ANSI (American National Standards Institute) standard, there are many different versions of the SQL language.

However, to be compliant with the ANSI standard, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

Note: Most of the SQL database programs also have their own proprietary extensions in addition to the SQL standard!

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Using SQL in Your Web Site

To build a web site that shows some data from a database, you will need the following:

• An RDBMS database program (i.e. MS Access, SQL Server, MySQL)
• A server-side scripting language, like PHP or ASP
• SQL
• HTML / CSS

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RDBMS

RDBMS stands for Relational Database Management System.

RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

The data in RDBMS is stored in database objects called tables.

A table is a collections of related data entries and it consists of columns and rows.

SQL is a database computer language designed for the retrieval and management of data in relational database. SQL stands for Structured Query Language.  This tutorial will give you quick start with SQL.

The SQL LIKE clause is used to compare a value to similar values using wildcard operators. There are two wildcards used in conjunction with the LIKE operator:

• The percent sign (%)
• The underscore (_)

The percent sign represents zero, one, or multiple characters. The underscore represents a single number or character. The symbols can be used in combinations.

Syntax:

The basic syntax of % and _ is as follows:

SELECT FROM table_name WHERE column LIKE 'XXXX%' or SELECT FROM table_name WHERE column LIKE '%XXXX%' or SELECT FROM table_name WHERE column LIKE 'XXXX_' or SELECT FROM table_name WHERE column LIKE '_XXXX' or SELECT FROM table_name WHERE column LIKE '_XXXX_'

You can combine N number of conditions using AND or OR operators. Here XXXX could be any numberic or string value.

Example:

Here are number of examples showing WHERE part having different LIKE clause with '%' and '_' operators:

Statement	Description
WHERE SALARY LIKE '200%'	Finds any values that start with 200
WHERE SALARY LIKE '%200%'	Finds any values that have 200 in any position
WHERE SALARY LIKE '_00%'	Finds any values that have 00 in the second and third positions
WHERE SALARY LIKE '2_%_%'	Finds any values that start with 2 and are at least 3 characters in length
WHERE SALARY LIKE '%2'	Finds any values that end with 2
WHERE SALARY LIKE '_2%3'	Finds any values that have a 2 in the second position and end with a 3
WHERE SALARY LIKE '2___3'	Finds any values in a five-digit number that start with 2 and end with 3

Let us take a real example, consider CUSTOMERS table is having following records:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

Following is an example which would display all the records from CUSTOMERS table where SALARY starts with 200:

SQL> SELECT * FROM CUSTOMERS WHERE SALARY LIKE '200%';

This would produce following result:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 3 | kaushik | 23 | Kota | 2000.00 | +----+----------+-----+-----------+----------+

The HAVING clause enables you to specify conditions that filter which group results appear in the final results.

The WHERE clause places conditions on the selected columns, whereas the HAVING clause places conditions on groups created by the GROUP BY clause.

Syntax:

The following is the position of the HAVING clause in a query:

SELECT FROM WHERE GROUP BY HAVING ORDER BY

The HAVING clause must follow the GROUP BY clause in a query and must also precede the ORDER BY clause if used. The following is the syntax of the SELECT statement, including the HAVING clause:

SELECT column1, column2 FROM table1, table2 WHERE [ conditions ] GROUP BY column1, column2 HAVING [ conditions ] ORDER BY column1, column2

Example:

Consider CUSTOMERS table is having following records:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

Following is the example which would display record for which similar age count would be more than or equal to 2:

SQL > SELECT * FROM CUSTOMERS GROUP BY age HAVING COUNT(age) >= 2;

This would produce following result:

+----+--------+-----+---------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+--------+-----+---------+---------+ | 2 | Khilan | 25 | Delhi | 1500.00 | +----+--------+-----+---------+---------+

SQL - Useful Resources

• 
  
  ANSI SQL - Database Language SQL (Proposed revised text of DIS 9075) July 1992 (Second Informal Review Draft).
  
  
• 
  
  Structured Query Language (SQL): - DB2 resource for SQL users.
  
  
• 
  
  Oracle SQL Developer - Oracle SQL Developer is a free and fully supported graphical tool for database development.
  
  
• 
  
  SQL at Wikipedia - A small article on SQL, worth to go through it.
  
  
• 
  
  MySQL Official Website - Here you can download the latest MySQL release, get the MySQL news update. The mailing list is also a great resources for anyone who want to build dynamic websites using MySQL.
  
  
• 
  
  MySQL and PERL - Its a tutorial from Tutorials Point which explains you how to use MySQL along with PERL and DBI module. Here you will learn all the required MySQL operations alongwith examples.

SQL has many built-in functions for performing processing on string or numeric data. Following is the list of all useful SQL built-in functions:

• SQL COUNT Function - The SQL COUNT aggregate function is used to count the number of rows in a database table.
• SQL MAX Function - The SQL MAX aggregate function allows us to select the highest (maximum) value for a certain column.
• SQL MIN Function - The SQL MIN aggregate function allows us to select the lowest (minimum) value for a certain column.
• SQL AVG Function - The SQL AVG aggregate function selects the average value for certain table column.
• SQL SUM Function - The SQL SUM aggregate function allows selecting the total for a numeric column.
• SQL SQRT Functions - This is used to generate a square root of a given number.
• SQL RAND Function - This is used to generate a random number using SQL command.
• SQL CONCAT Function - This is used to concatenate any string inside any SQL command.
• SQL Numeric Functions - Complete list of SQL functions required to manipulate numbers in SQL.
• SQL String Functions - Complete list of SQL functions required to manipulate strings in SQL.
  
  

If you take user input through a webpage and insert it into a SQL database there's a chance that you have left yourself wide open for a security issue known as SQL Injection.

This lesson will teach you how to help prevent this from happening and help you secure your scripts and SQL statements in your server side scripts such as PERL Script.

Injection usually occurs when you ask a user for input, like their name, and instead of a name they give you a SQL statement that you will unknowingly run on your database.

Never trust user provided data, process this data only after validation; as a rule, this is done by pattern matching.

In the example below, the name is restricted to alphanumerical chars plus underscore and to a length between 8 and 20 chars (Modify these rules as needed).

if (preg_match("/^\w{8,20}$/", $_GET['username'], $matches)) { $result = mysql_query("SELECT * FROM CUSTOMERS WHERE name=$matches[0]"); } else { echo "user name not accepted"; }

To demonstrate the problem, consider this excerpt:

// supposed input $name = "Qadir'; DELETE FROM CUSTOMERS;"; mysql_query("SELECT * FROM CUSTOMSRS WHERE name='{$name}'");

The function call is supposed to retrieve a record from the CUSTOMERS table where the name column matches the name specified by the user. Under normal circumstances, $name would only contain alphanumeric characters and perhaps spaces, such as the string ilia. But here, by appending an entirely new query to $name, the call to the database turns into disaster: the injected DELETE query removes all records from CUSTOMERS.

Fortunately, if you use MySQL, the mysql_query() function does not permit query stacking, or executing multiple SQL queries in a single function call. If you try to stack queries, the call fails.

However, other PHP database extensions, such as SQLite and PostgreSQL, happily perform stacked queries, executing all of the queries provided in one string and creating a serious security problem.

Preventing SQL Injection:

You can handle all escape characters smartly in scripting languages like PERL and PHP. The MySQL extension for PHP provides the function mysql_real_escape_string() to escape input characters that are special to MySQL.

if (get_magic_quotes_gpc()) { $name = stripslashes($name); } $name = mysql_real_escape_string($name); mysql_query("SELECT * FROM CUSTOMERS WHERE name='{$name}'");

The LIKE Quandary:

To address the LIKE quandary, a custom escaping mechanism must convert user-supplied % and _ characters to literals. Use addcslashes(), a function that let's you specify a character range to escape.

$sub = addcslashes(mysql_real_escape_string("%str"), "%_"); // $sub == \%str\_ mysql_query("SELECT * FROM messages WHERE subject LIKE '{$sub}%'");

There may be a situation when you have multiple duplicate records in a table. While fetching such records, it makes more sense to fetch only unique records instead of fetching duplicate records.

The SQL DISTINCT keyword, which we already have discussed, is used in conjunction with SELECT statement to eliminate all the duplicate records and fetching only unique records.

Syntax:

The basic syntax of DISTINCT keyword to eliminate duplicate records is as follows:

SELECT DISTINCT column1, column2,.....columnN FROM table_name WHERE [condition]

Example:

Consider CUSTOMERS table is having following records:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

First let us see how the following SELECT query returns duplicate salary records:

SQL> SELECT SALARY FROM CUSTOMERS ORDER BY SALARY;

This would produce following result where salary 2000 is coming twice which is a duplicate record from the original table.

+----------+ | SALARY | +----------+ | 1500.00 | | 2000.00 | | 2000.00 | | 4500.00 | | 6500.00 | | 8500.00 | | 10000.00 | +----------+

Now let us use DISTINCT keywork with the above SELECT query and see the result:

SQL> SELECT DISTINCT SALARY FROM CUSTOMERS ORDER BY SALARY;

This would produce following result where we do not have any duplicate entry:

+----------+ | SALARY | +----------+ | 1500.00 | | 2000.00 | | 4500.00 | | 6500.00 | | 8500.00 | | 10000.00 | +----------+

A sequence is a set of integers 1, 2, 3, ... that are generated in order on demand. Sequences are frequently used in databases because many applications require each row in a table to contain a unique value, and sequences provide an easy way to generate them.

This chapter describes how to use sequences in MySQL.

Using AUTO_INCREMENT column:

The simplest way in MySQL to use Sequences is to define a column as AUTO_INCREMENT and leave rest of the things to MySQL to take care.

Example:

Try out following example. This will create table and after that it will insert few rows in this table where it is not required to give record ID because its auto incremented by MySQL.

mysql> CREATE TABLE INSECT -> ( -> id INT UNSIGNED NOT NULL AUTO_INCREMENT, -> PRIMARY KEY (id), -> name VARCHAR(30) NOT NULL, # type of insect -> date DATE NOT NULL, # date collected -> origin VARCHAR(30) NOT NULL # where collected ); Query OK, 0 rows affected (0.02 sec) mysql> INSERT INTO INSECT (id,name,date,origin) VALUES -> (NULL,'housefly','2001-09-10','kitchen'), -> (NULL,'millipede','2001-09-10','driveway'), -> (NULL,'grasshopper','2001-09-10','front yard'); Query OK, 3 rows affected (0.02 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM INSECT ORDER BY id; +----+-------------+------------+------------+ | id | name | date | origin | +----+-------------+------------+------------+ | 1 | housefly | 2001-09-10 | kitchen | | 2 | millipede | 2001-09-10 | driveway | | 3 | grasshopper | 2001-09-10 | front yard | +----+-------------+------------+------------+ 3 rows in set (0.00 sec)

Obtain AUTO_INCREMENT Values:

LAST_INSERT_ID( ) is a SQL function, so you can use it from within any client that understands how to issue SQL statements. otherwise PERL and PHH scripts provide exclusive functions to retrieve auto incremented value of last record.

PERL Example:

Use the mysql_insertid attribute to obtain the AUTO_INCREMENT value generated by a query. This attribute is accessed through either a database handle or a statement handle, depending on how you issue the query. The following example references it through the database handle:

$dbh->do ("INSERT INTO INSECT (name,date,origin) VALUES('moth','2001-09-14','windowsill')"); my $seq = $dbh->{mysql_insertid};

PHP Example:

After issuing a query that generates an AUTO_INCREMENT value, retrieve the value by calling mysql_insert_id( ):

mysql_query ("INSERT INTO INSECT (name,date,origin) VALUES('moth','2001-09-14','windowsill')", $conn_id); $seq = mysql_insert_id ($conn_id);

Renumbering an Existing Sequence:

There may be a case when you have deleted many records from a table and you want to resequence all the records. This can be done by using a simple trick but you should be very careful to do so if your table is having join with other table.

If you determine that resequencing an AUTO_INCREMENT column is unavoidable, the way to do it is to drop the column from the table, then add it again. The following example shows how to renumber the id values in the insect table using this technique:

mysql> ALTER TABLE INSECT DROP id; mysql> ALTER TABLE insect -> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST, -> ADD PRIMARY KEY (id);

Starting a Sequence at a Particular Value:

By default MySQL will start sequence from 1 but you can specify any other number as well at the time of table creation. Following is the example where MySQL will start sequence from 100.

mysql> CREATE TABLE INSECT -> ( -> id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100, -> PRIMARY KEY (id), -> name VARCHAR(30) NOT NULL, # type of insect -> date DATE NOT NULL, # date collected -> origin VARCHAR(30) NOT NULL # where collected );

Alternatively, you can create the table and then set the initial sequence value with ALTER TABLE.

mysql> ALTER TABLE t AUTO_INCREMENT = 100;

A Subquery or Inner query or Nested query is a query within another SQL query, and embedded within the WHERE clause.

A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved.

Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN etc.

There are a few rules that subqueries must follow:

• Subqueries must be enclosed within parentheses.
• A subquery can have only one column in the SELECT clause, unless multiple columns are in the main query for the subquery to compare its selected columns.
• An ORDER BY cannot be used in a subquery, although the main query can use an ORDER BY. The GROUP BY can be used to perform the same function as the ORDER BY in a subquery.
• Subqueries that return more than one row can only be used with multiple value operators, such as the IN operator.
• The SELECT list cannot include any references to values that evaluate to a BLOB, ARRAY, CLOB, or NCLOB.
• A subquery cannot be immediately enclosed in a set function.
• The BETWEEN operator cannot be used with a subquery; however, the BETWEEN can be used within the subquery.

Subqueries with the SELECT Statement:

Subqueries are most frequently used with the SELECT statement. The basic syntax is as follows:

SELECT column_name [, column_name ] FROM table1 [, table2 ] WHERE column_name OPERATOR (SELECT column_name [, column_name ] FROM table1 [, table2 ] [WHERE])

Example:

Consider CUSTOMERS table is having following records:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 35 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

Now let us check following sub-query with SELECT statement:

SQL> SELECT * FROM CUSTOMERS WHERE ID IN (SELECT ID FROM CUSTOMERS WHERE SALARY > 4500) ;

This would produce following result:

+----+----------+-----+---------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+---------+----------+ | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+---------+----------+

Subqueries with the INSERT Statement:

Subqueries also can be used with INSERT statements. The INSERT statement uses the data returned from the subquery to insert into another table. The selected data in the subquery can be modified with any of the character, date, or number functions.

The basic syntax is as follows:

INSERT INTO table_name [ (column1 [, column2 ]) ] SELECT [ *|column1 [, column2 ] FROM table1 [, table2 ] [ WHERE VALUE OPERATOR ]

Example:

Consider a table CUSTOMERS_BKP with similar structure as CUSTOMERS table. Now to copy complete CUSTOMERS table into CUSTOMERS_BKP, following is the syntax:

SQL> INSERT INTO CUSTOMERS_BKP SELECT * FROM CUSTOMERS WHERE ID IN (SELECT ID FROM CUSTOMERS) ;

Subqueries with the UPDATE Statement:

The subquery can be used in conjunction with the UPDATE statement. Either single or multiple columns in a table can be updated when using a subquery with the UPDATE statement.

The basic syntax is as follows:

UPDATE table SET column_name = new_value [ WHERE OPERATOR [ VALUE ] (SELECT COLUMN_NAME FROM TABLE_NAME) [ WHERE) ]

Example:

Assuming, we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table.

Following example updates SALARY by 0.25 times in CUSTOMERS table for all the customers whose AGE is greater than or equal to 27:

SQL> UPDATE CUSTOMERS SET SALARY = SALARY * 0.25 WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP WHERE AGE >= 27 );

This would impact two rows and finally CUSTOMERS table would have following records:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 35 | Ahmedabad | 125.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 2125.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

Subqueries with the DELETE Statement:

The subquery can be used in conjunction with the DELETE statement like with any other statements mentioned above.

The basic syntax is as follows:

DELETE FROM TABLE_NAME [ WHERE OPERATOR [ VALUE ] (SELECT COLUMN_NAME FROM TABLE_NAME) [ WHERE) ]

Example:

Assuming, we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table.

Following example deletes records from CUSTOMERS table for all the customers whose AGE is greater than or equal to 27:

SQL> DELETE FROM CUSTOMERS WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP WHERE AGE > 27 );

This would impact two rows and finally CUSTOMERS table would have following records:

+----+----------+-----+---------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+---------+----------+ | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+---------+----------+

There may be a situation when you need an exact copy of a table, and CREATE TABLE ... SELECT... doesn't suit your purposes because the copy must include the same indexes, default values, and so forth.

If you are using MySQL RDBMS, you can handle this situation by following steps.

1. Use SHOW CREATE TABLE command to get a CREATE TABLE statement that specifies the source table's structure, indexes and all.
2. Modify the statement to change the table name to that of the clone table and execute the statement. This way you will have exact clone table.
3. Optionally, If you need the table contents copied as well, issue an INSERT INTO ... SELECT statement, too.

Example:

Try out following example to create a clone table for TUTORIALS_TBL whose structure is as follows:

Step 1:

Get complete structure about table

SQL> SHOW CREATE TABLE TUTORIALS_TBL \G; *************************** 1. row *************************** Table: TUTORIALS_TBL Create Table: CREATE TABLE `TUTORIALS_TBL` ( `tutorial_id` int(11) NOT NULL auto_increment, `tutorial_title` varchar(100) NOT NULL default '', `tutorial_author` varchar(40) NOT NULL default '', `submission_date` date default NULL, PRIMARY KEY (`tutorial_id`), UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`) ) TYPE=MyISAM 1 row in set (0.00 sec)

Step 2:

Rename this table and create another table

SQL> CREATE TABLE `CLONE_TBL` ( -> `tutorial_id` int(11) NOT NULL auto_increment, -> `tutorial_title` varchar(100) NOT NULL default '', -> `tutorial_author` varchar(40) NOT NULL default '', -> `submission_date` date default NULL, -> PRIMARY KEY (`tutorial_id`), -> UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`) -> ) TYPE=MyISAM; Query OK, 0 rows affected (1.80 sec)

Step 3:

After executing step 2 you will a clone table in your database. If you want to copy data from old table then you can do it by using INSERT INTO... SELECT statement.

SQL> INSERT INTO CLONE_TBL (tutorial_id, -> tutorial_title, -> tutorial_author, -> submission_date) -> SELECT tutorial_id,tutorial_title, -> tutorial_author,submission_date, -> FROM TUTORIALS_TBL; Query OK, 3 rows affected (0.07 sec) Records: 3 Duplicates: 0 Warnings: 0

Finally you will have exact clone table as you wanted to have.

There are RDBMS which support temporary tables. Temporary Tables are a great feature that lets you store and process intermediate results by using the same selection, update, and join capabilities that you can use with typical SQL Server tables.

The temporary tables could be very useful in some cases to keep temporary data. The most important thing that should be knows for temporary tables is that they will be deleted when the current client session terminates.

Temporary tables are available in MySQL version 3.23 onwards. If you use an older version of MySQL than 3.23 you can't use temporary tables, but you can use heap tables.

As stated earlier temporary tables will only last as long as the session is alive. If you run the code in a PHP script, the temporary table will be destroyed automatically when the script finishes executing. If you are connected to the MySQL database server through the MySQL client program, then the temporary table will exist until you close the client or manually destroy the table.

Example

Here is an example showing you usage of temporary table:

mysql> CREATE TEMPORARY TABLE SALESSUMMARY ( -> product_name VARCHAR(50) NOT NULL -> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00 -> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00 -> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0 ); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO SALESSUMMARY -> (product_name, total_sales, avg_unit_price, total_units_sold) -> VALUES -> ('cucumber', 100.25, 90, 2); mysql> SELECT * FROM SALESSUMMARY; +--------------+-------------+----------------+------------------+ | product_name | total_sales | avg_unit_price | total_units_sold | +--------------+-------------+----------------+------------------+ | cucumber | 100.25 | 90.00 | 2 | +--------------+-------------+----------------+------------------+ 1 row in set (0.00 sec)

When you issue a SHOW TABLES command then your temporary table would not be listed out in the list. Now if you will log out of the MySQL session and then you will issue a SELECT command then you will find no data available in the database. Even your temporary table would also not exist.

Dropping Temporary Tables:

By default all the temporary tables are deleted by MySQL when your database connection gets terminated. Still you want to delete them in between then you do so by issuing DROP TABLE command.

Following is the example on dropping a temproary table.

mysql> CREATE TEMPORARY TABLE SALESSUMMARY ( -> product_name VARCHAR(50) NOT NULL -> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00 -> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00 -> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0 ); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO SALESSUMMARY -> (product_name, total_sales, avg_unit_price, total_units_sold) -> VALUES -> ('cucumber', 100.25, 90, 2); mysql> SELECT * FROM SALESSUMMARY; +--------------+-------------+----------------+------------------+ | product_name | total_sales | avg_unit_price | total_units_sold | +--------------+-------------+----------------+------------------+ | cucumber | 100.25 | 90.00 | 2 | +--------------+-------------+----------------+------------------+ 1 row in set (0.00 sec) mysql> DROP TABLE SALESSUMMARY; mysql> SELECT * FROM SALESSUMMARY; ERROR 1146: Table 'TUTORIALS.SALESSUMMARY' doesn't exist

Following is the list of all important Date and Time related functions available through SQL. There are various other functions supported by your RDBMS. Given list is based on MySQL RDBMS.

Name	Description
ADDDATE()	Add dates
ADDTIME()	Add time
CONVERT_TZ()	Convert from one timezone to another
CURDATE()	Return the current date
CURRENT_DATE(), CURRENT_DATE	Synonyms for CURDATE()
CURRENT_TIME(), CURRENT_TIME	Synonyms for CURTIME()
CURRENT_TIMESTAMP(), CURRENT_TIMESTAMP	Synonyms for NOW()
CURTIME()	Return the current time
DATE_ADD()	Add two dates
DATE_FORMAT()	Format date as specified
DATE_SUB()	Subtract two dates
DATE()	Extract the date part of a date or datetime expression
DATEDIFF()	Subtract two dates
DAY()	Synonym for DAYOFMONTH()
DAYNAME()	Return the name of the weekday
DAYOFMONTH()	Return the day of the month (1-31)
DAYOFWEEK()	Return the weekday index of the argument
DAYOFYEAR()	Return the day of the year (1-366)
EXTRACT	Extract part of a date
FROM_DAYS()	Convert a day number to a date
FROM_UNIXTIME()	Format date as a UNIX timestamp
HOUR()	Extract the hour
LAST_DAY	Return the last day of the month for the argument
LOCALTIME(), LOCALTIME	Synonym for NOW()
LOCALTIMESTAMP, LOCALTIMESTAMP()	Synonym for NOW()
MAKEDATE()	Create a date from the year and day of year
MAKETIME	MAKETIME()
MICROSECOND()	Return the microseconds from argument
MINUTE()	Return the minute from the argument
MONTH()	Return the month from the date passed
MONTHNAME()	Return the name of the month
NOW()	Return the current date and time
PERIOD_ADD()	Add a period to a year-month
PERIOD_DIFF()	Return the number of months between periods
QUARTER()	Return the quarter from a date argument
SEC_TO_TIME()	Converts seconds to 'HH:MM:SS' format
SECOND()	Return the second (0-59)
STR_TO_DATE()	Convert a string to a date
SUBDATE()	When invoked with three arguments a synonym for DATE_SUB()
SUBTIME()	Subtract times
SYSDATE()	Return the time at which the function executes
TIME_FORMAT()	Format as time
TIME_TO_SEC()	Return the argument converted to seconds
TIME()	Extract the time portion of the expression passed
TIMEDIFF()	Subtract time
TIMESTAMP()	With a single argument, this function returns the date or datetime expression. With two arguments, the sum of the arguments
TIMESTAMPADD()	Add an interval to a datetime expression
TIMESTAMPDIFF()	Subtract an interval from a datetime expression
TO_DAYS()	Return the date argument converted to days
UNIX_TIMESTAMP()	Return a UNIX timestamp
UTC_DATE()	Return the current UTC date
UTC_TIME()	Return the current UTC time
UTC_TIMESTAMP()	Return the current UTC date and time
WEEK()	Return the week number
WEEKDAY()	Return the weekday index
WEEKOFYEAR()	Return the calendar week of the date (1-53)
YEAR()	Return the year
YEARWEEK()	Return the year and week

ADDDATE(date,INTERVAL expr unit), ADDDATE(expr,days)

When invoked with the INTERVAL form of the second argument, ADDDATE() is a synonym for DATE_ADD(). The related function SUBDATE() is a synonym for DATE_SUB(). For information on the INTERVAL unit argument, see the discussion for DATE_ADD().

mysql> SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY); +---------------------------------------------------------+ | DATE_ADD('1998-01-02', INTERVAL 31 DAY) | +---------------------------------------------------------+ | 1998-02-02 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT ADDDATE('1998-01-02', INTERVAL 31 DAY); +---------------------------------------------------------+ | ADDDATE('1998-01-02', INTERVAL 31 DAY) | +---------------------------------------------------------+ | 1998-02-02 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

When invoked with the days form of the second argument, MySQL treats it as an integer number of days to be added to expr.

mysql> SELECT ADDDATE('1998-01-02', 31); +---------------------------------------------------------+ | DATE_ADD('1998-01-02', INTERVAL 31 DAY) | +---------------------------------------------------------+ | 1998-02-02 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

ADDTIME(expr1,expr2)

ADDTIME() adds expr2 to expr1 and returns the result. expr1 is a time or datetime expression, and expr2 is a time expression.

mysql> SELECT ADDTIME('1997-12-31 23:59:59.999999','1 1:1:1.000002'); +---------------------------------------------------------+ | DATE_ADD('1997-12-31 23:59:59.999999','1 1:1:1.000002') | +---------------------------------------------------------+ | 1998-01-02 01:01:01.000001 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

CONVERT_TZ(dt,from_tz,to_tz)

This converts a datetime value dt from the time zone given by from_tz to the time zone given by to_tz and returns the resulting value. This function returns NULL if the arguments are invalid.

mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','GMT','MET'); +---------------------------------------------------------+ | CONVERT_TZ('2004-01-01 12:00:00','GMT','MET') | +---------------------------------------------------------+ | 2004-01-01 13:00:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00'); +---------------------------------------------------------+ | CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00') | +---------------------------------------------------------+ | 2004-01-01 22:00:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

CURDATE()

Returns the current date as a value in 'YYYY-MM-DD' or YYYYMMDD format, depending on whether the function is used in a string or numeric context.

mysql> SELECT CURDATE(); +---------------------------------------------------------+ | CURDATE() | +---------------------------------------------------------+ | 1997-12-15 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT CURDATE() + 0; +---------------------------------------------------------+ | CURDATE() + 0 | +---------------------------------------------------------+ | 19971215 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

CURRENT_DATE and CURRENT_DATE()

CURRENT_DATE and CURRENT_DATE() are synonyms for CURDATE()

CURTIME()

Returns the current time as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context. The value is expressed in the current time zone.

mysql> SELECT CURTIME(); +---------------------------------------------------------+ | CURTIME() | +---------------------------------------------------------+ | 23:50:26 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT CURTIME() + 0; +---------------------------------------------------------+ | CURTIME() + 0 | +---------------------------------------------------------+ | 235026 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

CURRENT_TIME and CURRENT_TIME()

CURRENT_TIME and CURRENT_TIME() are synonyms for CURTIME().

CURRENT_TIMESTAMP and CURRENT_TIMESTAMP()

CURRENT_TIMESTAMP and CURRENT_TIMESTAMP() are synonyms for NOW().

DATE(expr)

Extracts the date part of the date or datetime expression expr.

mysql> SELECT DATE('2003-12-31 01:02:03'); +---------------------------------------------------------+ | DATE('2003-12-31 01:02:03') | +---------------------------------------------------------+ | 2003-12-31 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DATEDIFF(expr1,expr2)

DATEDIFF() returns expr1 . expr2 expressed as a value in days from one date to the other. expr1 and expr2 are date or date-and-time expressions. Only the date parts of the values are used in the calculation.

mysql> SELECT DATEDIFF('1997-12-31 23:59:59','1997-12-30'); +---------------------------------------------------------+ | DATEDIFF('1997-12-31 23:59:59','1997-12-30') | +---------------------------------------------------------+ | 1 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DATE_ADD(date,INTERVAL expr unit), DATE_SUB(date,INTERVAL expr unit)

These functions perform date arithmetic. date is a DATETIME or DATE value specifying the starting date. expr is an expression specifying the interval value to be added or subtracted from the starting date. expr is a string; it may start with a .-. for negative intervals. unit is a keyword indicating the units in which the expression should be interpreted.

The INTERVAL keyword and the unit specifier are not case sensitive.

The following table shows the expected form of the expr argument for each unit value;

unit Value	ExpectedexprFormat
MICROSECOND	MICROSECONDS
SECOND	SECONDS
MINUTE	MINUTES
HOUR	HOURS
DAY	DAYS
WEEK	WEEKS
MONTH	MONTHS
QUARTER	QUARTERS
YEAR	YEARS
SECOND_MICROSECOND	'SECONDS.MICROSECONDS'
MINUTE_MICROSECOND	'MINUTES.MICROSECONDS'
MINUTE_SECOND	'MINUTES:SECONDS'
HOUR_MICROSECOND	'HOURS.MICROSECONDS'
HOUR_SECOND	'HOURS:MINUTES:SECONDS'
HOUR_MINUTE	'HOURS:MINUTES'
DAY_MICROSECOND	'DAYS.MICROSECONDS'
DAY_SECOND	'DAYS HOURS:MINUTES:SECONDS'
DAY_MINUTE	'DAYS HOURS:MINUTES'
DAY_HOUR	'DAYS HOURS'
YEAR_MONTH	'YEARS-MONTHS'

The values QUARTER and WEEK are available beginning with MySQL 5.0.0.

mysql> SELECT DATE_ADD('1997-12-31 23:59:59', -> INTERVAL '1:1' MINUTE_SECOND); +---------------------------------------------------------+ | DATE_ADD('1997-12-31 23:59:59', INTERVAL... | +---------------------------------------------------------+ | 1998-01-01 00:01:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT DATE_ADD('1999-01-01', INTERVAL 1 HOUR); +---------------------------------------------------------+ | DATE_ADD('1999-01-01', INTERVAL 1 HOUR) | +---------------------------------------------------------+ | 1999-01-01 01:00:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DATE_FORMAT(date,format)

Formats the date value according to the format string.

The following specifiers may be used in the format string. The .%. character is required before format specifier characters.

Specifier	Description
%a	Abbreviated weekday name (Sun..Sat)
%b	Abbreviated month name (Jan..Dec)
%c	Month, numeric (0..12)
%D	Day of the month with English suffix (0th, 1st, 2nd, 3rd, .)
%d	Day of the month, numeric (00..31)
%e	Day of the month, numeric (0..31)
%f	Microseconds (000000..999999)
%H	Hour (00..23)
%h	Hour (01..12)
%I	Hour (01..12)
%i	Minutes, numeric (00..59)
%j	Day of year (001..366)
%k	Hour (0..23)
%l	Hour (1..12)
%M	Month name (January..December)
%m	Month, numeric (00..12)
%p	AM or PM
%r	Time, 12-hour (hh:mm:ss followed by AM or PM)
%S	Seconds (00..59)
%s	Seconds (00..59)
%T	Time, 24-hour (hh:mm:ss)
%U	Week (00..53), where Sunday is the first day of the week
%u	Week (00..53), where Monday is the first day of the week
%V	Week (01..53), where Sunday is the first day of the week; used with %X
%v	Week (01..53), where Monday is the first day of the week; used with %x
%W	Weekday name (Sunday..Saturday)
%w	Day of the week (0=Sunday..6=Saturday)
%X	Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V
%x	Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v
%Y	Year, numeric, four digits
%y	Year, numeric (two digits)
%%	A literal .%. character
%x	x, for any.x. not listed above

mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y'); +---------------------------------------------------------+ | DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y') | +---------------------------------------------------------+ | Saturday October 1997 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00' -> '%H %k %I %r %T %S %w'); +---------------------------------------------------------+ | DATE_FORMAT('1997-10-04 22:23:00....... | +---------------------------------------------------------+ | 22 22 10 10:23:00 PM 22:23:00 00 6 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DATE_SUB(date,INTERVAL expr unit)

This is similar to DATE_ADD() function.

DAY(date)

DAY() is a synonym for DAYOFMONTH().

DAYNAME(date)

Returns the name of the weekday for date.

mysql> SELECT DAYNAME('1998-02-05'); +---------------------------------------------------------+ | DAYNAME('1998-02-05') | +---------------------------------------------------------+ | Thursday | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DAYOFMONTH(date)

Returns the day of the month for date, in the range 0 to 31.

mysql> SELECT DAYOFMONTH('1998-02-03'); +---------------------------------------------------------+ | DAYOFMONTH('1998-02-03') | +---------------------------------------------------------+ | 3 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DAYOFWEEK(date)

Returns the weekday index for date (1 = Sunday, 2 = Monday, ., 7 = Saturday). These index values correspond to the ODBC standard.

mysql> SELECT DAYOFWEEK('1998-02-03'); +---------------------------------------------------------+ |DAYOFWEEK('1998-02-03') | +---------------------------------------------------------+ | 3 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

DAYOFYEAR(date)

Returns the day of the year for date, in the range 1 to 366.

mysql> SELECT DAYOFYEAR('1998-02-03'); +---------------------------------------------------------+ | DAYOFYEAR('1998-02-03') | +---------------------------------------------------------+ | 34 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

EXTRACT(unit FROM date)

The EXTRACT() function uses the same kinds of unit specifiers as DATE_ADD() or DATE_SUB(), but extracts parts from the date rather than performing date arithmetic.

mysql> SELECT EXTRACT(YEAR FROM '1999-07-02'); +---------------------------------------------------------+ | EXTRACT(YEAR FROM '1999-07-02') | +---------------------------------------------------------+ | 1999 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT EXTRACT(YEAR_MONTH FROM '1999-07-02 01:02:03'); +---------------------------------------------------------+ | EXTRACT(YEAR_MONTH FROM '1999-07-02 01:02:03') | +---------------------------------------------------------+ | 199907 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

FROM_DAYS(N)

Given a day number N, returns a DATE value.

mysql> SELECT FROM_DAYS(729669); +---------------------------------------------------------+ | FROM_DAYS(729669) | +---------------------------------------------------------+ | 1997-10-07 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

Use FROM_DAYS() with caution on old dates. It is not intended for use with values that precede the advent of the Gregorian calendar (1582).

FROM_UNIXTIME(unix_timestamp)

FROM_UNIXTIME(unix_timestamp,format)

Returns a representation of the unix_timestamp argument as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context. The value is expressed in the current time zone. unix_timestamp is an internal timestamp value such as is produced by the UNIX_TIMESTAMP() function.

If format is given, the result is formatted according to the format string, which is used the same way as listed in the entry for the DATE_FORMAT() function.

mysql> SELECT FROM_UNIXTIME(875996580); +---------------------------------------------------------+ | FROM_UNIXTIME(875996580) | +---------------------------------------------------------+ | 1997-10-04 22:23:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

HOUR(time)

Returns the hour for time. The range of the return value is 0 to 23 for time-of-day values. However, the range of TIME values actually is much larger, so HOUR can return values greater than 23.

mysql> SELECT HOUR('10:05:03'); +---------------------------------------------------------+ | HOUR('10:05:03') | +---------------------------------------------------------+ | 10 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

LAST_DAY(date)

Takes a date or datetime value and returns the corresponding value for the last day of the month. Returns NULL if the argument is invalid.

mysql> SELECT LAST_DAY('2003-02-05'); +---------------------------------------------------------+ | LAST_DAY('2003-02-05') | +---------------------------------------------------------+ | 2003-02-28 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

LOCALTIME and LOCALTIME()

LOCALTIME and LOCALTIME() are synonyms for NOW().

LOCALTIMESTAMP and LOCALTIMESTAMP()

LOCALTIMESTAMP and LOCALTIMESTAMP() are synonyms for NOW().

MAKEDATE(year,dayofyear)

Returns a date, given year and day-of-year values. dayofyear must be greater than 0 or the result is NULL.

mysql> SELECT MAKEDATE(2001,31), MAKEDATE(2001,32); +---------------------------------------------------------+ | MAKEDATE(2001,31), MAKEDATE(2001,32) | +---------------------------------------------------------+ | '2001-01-31', '2001-02-01' | +---------------------------------------------------------+ 1 row in set (0.00 sec)

MAKETIME(hour,minute,second)

Returns a time value calculated from the hour, minute, and second arguments.

mysql> SELECT MAKETIME(12,15,30); +---------------------------------------------------------+ | MAKETIME(12,15,30) | +---------------------------------------------------------+ | '12:15:30' | +---------------------------------------------------------+ 1 row in set (0.00 sec)

MICROSECOND(expr)

Returns the microseconds from the time or datetime expression expr as a number in the range from 0 to 999999.

mysql> SELECT MICROSECOND('12:00:00.123456'); +---------------------------------------------------------+ | MICROSECOND('12:00:00.123456') | +---------------------------------------------------------+ | 123456 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

MINUTE(time)

Returns the minute for time, in the range 0 to 59.

mysql> SELECT MINUTE('98-02-03 10:05:03'); +---------------------------------------------------------+ | MINUTE('98-02-03 10:05:03') | +---------------------------------------------------------+ | 5 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

MONTH(date)

Returns the month for date, in the range 0 to 12.

mysql> SELECT MONTH('1998-02-03') +---------------------------------------------------------+ | MONTH('1998-02-03') | +---------------------------------------------------------+ | 2 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

MONTHNAME(date)

Returns the full name of the month for date.

mysql> SELECT MONTHNAME('1998-02-05'); +---------------------------------------------------------+ | MONTHNAME('1998-02-05') | +---------------------------------------------------------+ | February | +---------------------------------------------------------+ 1 row in set (0.00 sec)

NOW()

Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context. The value is expressed in the current time zone.

mysql> SELECT NOW(); +---------------------------------------------------------+ | NOW() | +---------------------------------------------------------+ | 1997-12-15 23:50:26 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

PERIOD_ADD(P,N)

Adds N months to period P (in the format YYMM or YYYYMM). Returns a value in the format YYYYMM. Note that the period argument P is not a date value.

mysql> SELECT PERIOD_ADD(9801,2); +---------------------------------------------------------+ | PERIOD_ADD(9801,2) | +---------------------------------------------------------+ | 199803 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

PERIOD_DIFF(P1,P2)

Returns the number of months between periods P1 and P2. P1 and P2 should be in the format YYMM or YYYYMM. Note that the period arguments P1 and P2 are not date values.

mysql> SELECT PERIOD_DIFF(9802,199703); +---------------------------------------------------------+ | PERIOD_DIFF(9802,199703) | +---------------------------------------------------------+ | 11 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

QUARTER(date)

Returns the quarter of the year for date, in the range 1 to 4.

mysql> SELECT QUARTER('98-04-01'); +---------------------------------------------------------+ | QUARTER('98-04-01') | +---------------------------------------------------------+ | 2 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

SECOND(time)

Returns the second for time, in the range 0 to 59.

mysql> SELECT SECOND('10:05:03'); +---------------------------------------------------------+ | SECOND('10:05:03') | +---------------------------------------------------------+ | 3 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

SEC_TO_TIME(seconds)

Returns the seconds argument, converted to hours, minutes, and seconds, as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context.

mysql> SELECT SEC_TO_TIME(2378); +---------------------------------------------------------+ | SEC_TO_TIME(2378) | +---------------------------------------------------------+ | 00:39:38 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

STR_TO_DATE(str,format)

This is the inverse of the DATE_FORMAT() function. It takes a string str and a format string format. STR_TO_DATE() returns a DATETIME value if the format string contains both date and time parts, or a DATE or TIME value if the string contains only date or time parts.

mysql> SELECT STR_TO_DATE('04/31/2004', '%m/%d/%Y'); +---------------------------------------------------------+ | STR_TO_DATE('04/31/2004', '%m/%d/%Y') | +---------------------------------------------------------+ | 2004-04-31 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

SUBDATE(date,INTERVAL expr unit) and SUBDATE(expr,days)

When invoked with the INTERVAL form of the second argument, SUBDATE() is a synonym for DATE_SUB(). For information on the INTERVAL unit argument, see the discussion for DATE_ADD().

mysql> SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY); +---------------------------------------------------------+ | DATE_SUB('1998-01-02', INTERVAL 31 DAY) | +---------------------------------------------------------+ | 1997-12-02 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT SUBDATE('1998-01-02', INTERVAL 31 DAY); +---------------------------------------------------------+ | SUBDATE('1998-01-02', INTERVAL 31 DAY) | +---------------------------------------------------------+ | 1997-12-02 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

SUBTIME(expr1,expr2)

SUBTIME() returns expr1 . expr2 expressed as a value in the same format as expr1. expr1 is a time or datetime expression, and expr2 is a time.

mysql> SELECT SUBTIME('1997-12-31 23:59:59.999999', -> '1 1:1:1.000002'); +---------------------------------------------------------+ | SUBTIME('1997-12-31 23:59:59.999999'... | +---------------------------------------------------------+ | 1997-12-30 22:58:58.999997 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

SYSDATE()

Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context.

mysql> SELECT SYSDATE(); +---------------------------------------------------------+ | SYSDATE() | +---------------------------------------------------------+ | 2006-04-12 13:47:44 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIME(expr)

Extracts the time part of the time or datetime expression expr and returns it as a string.

mysql> SELECT TIME('2003-12-31 01:02:03'); +---------------------------------------------------------+ | TIME('2003-12-31 01:02:03') | +---------------------------------------------------------+ | 01:02:03 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIMEDIFF(expr1,expr2)

TIMEDIFF() returns expr1 . expr2 expressed as a time value. expr1 and expr2 are time or date-and-time expressions, but both must be of the same type.

mysql> SELECT TIMEDIFF('1997-12-31 23:59:59.000001', -> '1997-12-30 01:01:01.000002'); +---------------------------------------------------------+ | TIMEDIFF('1997-12-31 23:59:59.000001'..... | +---------------------------------------------------------+ | 46:58:57.999999 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIMESTAMP(expr), TIMESTAMP(expr1,expr2)

With a single argument, this function returns the date or datetime expression expr as a datetime value. With two arguments, it adds the time expression expr2 to the date or datetime expression expr1 and returns the result as a datetime value.

mysql> SELECT TIMESTAMP('2003-12-31'); +---------------------------------------------------------+ | TIMESTAMP('2003-12-31') | +---------------------------------------------------------+ | 2003-12-31 00:00:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIMESTAMPADD(unit,interval,datetime_expr)

Adds the integer expression interval to the date or datetime expression datetime_expr. The unit for interval is given by the unit argument, which should be one of the following values: FRAC_SECOND, SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.

The unit value may be specified using one of keywords as shown, or with a prefix of SQL_TSI_. For example, DAY and SQL_TSI_DAY both are legal.

mysql> SELECT TIMESTAMPADD(MINUTE,1,'2003-01-02'); +---------------------------------------------------------+ | TIMESTAMPADD(MINUTE,1,'2003-01-02') | +---------------------------------------------------------+ | 2003-01-02 00:01:00 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIMESTAMPDIFF(unit,datetime_expr1,datetime_expr2)

Returns the integer difference between the date or datetime expressions datetime_expr1 and datetime_expr2. The unit for the result is given by the unit argument. The legal values for unit are the same as those listed in the description of the TIMESTAMPADD() function.

mysql> SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01'); +---------------------------------------------------------+ | TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01') | +---------------------------------------------------------+ | 3 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIME_FORMAT(time,format)

This is used like the DATE_FORMAT() function, but the format string may contain format specifiers only for hours, minutes, and seconds.

If the time value contains an hour part that is greater than 23, the %H and %k hour format specifiers produce a value larger than the usual range of 0..23. The other hour format specifiers produce the hour value modulo 12.

mysql> SELECT TIME_FORMAT('100:00:00', '%H %k %h %I %l'); +---------------------------------------------------------+ | TIME_FORMAT('100:00:00', '%H %k %h %I %l') | +---------------------------------------------------------+ | 100 100 04 04 4 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TIME_TO_SEC(time)

Returns the time argument, converted to seconds.

mysql> SELECT TIME_TO_SEC('22:23:00'); +---------------------------------------------------------+ | TIME_TO_SEC('22:23:00') | +---------------------------------------------------------+ | 80580 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

TO_DAYS(date)

Given a date date, returns a day number (the number of days since year 0).

mysql> SELECT TO_DAYS(950501); +---------------------------------------------------------+ | TO_DAYS(950501) | +---------------------------------------------------------+ | 728779 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

UNIX_TIMESTAMP(), UNIX_TIMESTAMP(date)

If called with no argument, returns a Unix timestamp (seconds since '1970-01-01 00:00:00' UTC) as an unsigned integer. If UNIX_TIMESTAMP() is called with a date argument, it returns the value of the argument as seconds since '1970-01-01 00:00:00' UTC. date may be a DATE string, a DATETIME string, a TIMESTAMP, or a number in the format YYMMDD or YYYYMMDD.

mysql> SELECT UNIX_TIMESTAMP(); +---------------------------------------------------------+ | UNIX_TIMESTAMP() | +---------------------------------------------------------+ | 882226357 | +---------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT UNIX_TIMESTAMP('1997-10-04 22:23:00'); +---------------------------------------------------------+ | UNIX_TIMESTAMP('1997-10-04 22:23:00') | +---------------------------------------------------------+ | 875996580 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

UTC_DATE, UTC_DATE()

Returns the current UTC date as a value in 'YYYY-MM-DD' or YYYYMMDD format, depending on whether the function is used in a string or numeric context.

mysql> SELECT UTC_DATE(), UTC_DATE() + 0; +---------------------------------------------------------+ | UTC_DATE(), UTC_DATE() + 0 | +---------------------------------------------------------+ | 2003-08-14, 20030814 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

UTC_TIME, UTC_TIME()

Returns the current UTC time as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context.

mysql> SELECT UTC_TIME(), UTC_TIME() + 0; +---------------------------------------------------------+ | UTC_TIME(), UTC_TIME() + 0 | +---------------------------------------------------------+ | 18:07:53, 180753 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

UTC_TIMESTAMP, UTC_TIMESTAMP()

Returns the current UTC date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context.

mysql> SELECT UTC_TIMESTAMP(), UTC_TIMESTAMP() + 0; +---------------------------------------------------------+ | UTC_TIMESTAMP(), UTC_TIMESTAMP() + 0 | +---------------------------------------------------------+ | 2003-08-14 18:08:04, 20030814180804 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

WEEK(date[,mode])

This function returns the week number for date. The two-argument form of WEEK() allows you to specify whether the week starts on Sunday or Monday and whether the return value should be in the range from 0 to 53 or from 1 to 53. If the mode argument is omitted, the value of the default_week_format system variable is used

Mode	First Day of week	Range	Week 1 is the first week .
0	Sunday	0-53	with a Sunday in this year
1	Monday	0-53	with more than 3 days this year
2	Sunday	1-53	with a Sunday in this year
3	Monday	1-53	with more than 3 days this year
4	Sunday	0-53	with more than 3 days this year
5	Monday	0-53	with a Monday in this year
6	Sunday	1-53	with more than 3 days this year
7	Monday	1-53	with a Monday in this year

mysql> SELECT WEEK('1998-02-20'); +---------------------------------------------------------+ | WEEK('1998-02-20') | +---------------------------------------------------------+ | 7 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

WEEKDAY(date)

Returns the weekday index for date (0 = Monday, 1 = Tuesday, . 6 = Sunday).

mysql> SELECT WEEKDAY('1998-02-03 22:23:00'); +---------------------------------------------------------+ | WEEKDAY('1998-02-03 22:23:00') | +---------------------------------------------------------+ | 1 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

WEEKOFYEAR(date)

Returns the calendar week of the date as a number in the range from 1 to 53. WEEKOFYEAR() is a compatibility function that is equivalent to WEEK(date,3).

mysql> SELECT WEEKOFYEAR('1998-02-20'); +---------------------------------------------------------+ | WEEKOFYEAR('1998-02-20') | +---------------------------------------------------------+ | 8 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

YEAR(date)

Returns the year for date, in the range 1000 to 9999, or 0 for the .zero. date.

mysql> SELECT YEAR('98-02-03'); +---------------------------------------------------------+ | YEAR('98-02-03') | +---------------------------------------------------------+ | 1998 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

YEARWEEK(date), YEARWEEK(date,mode)

Returns year and week for a date. The mode argument works exactly like the mode argument to WEEK(). The year in the result may be different from the year in the date argument for the first and the last week of the year.

mysql> SELECT YEARWEEK('1987-01-01'); +---------------------------------------------------------+ | YEAR('98-02-03')YEARWEEK('1987-01-01') | +---------------------------------------------------------+ | 198653 | +---------------------------------------------------------+ 1 row in set (0.00 sec)

Note that the week number is different from what the WEEK() function would return (0) for optional arguments 0 or 1, as WEEK() then returns the week in the context of the given year.