SQL Functions

SQL has many built-in functions that enable you to perform calculations on data.

SQL Aggregate Functions

SQL aggregate functions perform calculation on a set of values and return a single value. The following table summarizes some useful aggregate functions:

Function	Description
`AVG()`	Returns the average of values
`SUM()`	Returns the sum of values
`COUNT()`	Returns the number of rows in a result set
`MAX()`	Returns the maximum value
`MIN()`	Returns the minimum value

SQL String Functions

SQL string functions perform operation on a string input value and return a string or numeric value. The following table summarizes some useful string functions:

Function	Description
`CONCAT()`	Returns a string by concatenating two or more string values.
`CONCAT_WS()`	Returns a string by concatenating two or more string values with a separator.
`FORMAT()`	Returns a value formatted with the specified format.
`LOWER()`	Converts a string to lowercase.
`UPPER()`	Converts a string to uppercase.
`TRIM()`	Remove leading and trailing spaces from a string.
`REVERSE()`	Returns the reverse order of a string value.
`SUBSTRING()`	Returns a substring from string.

SQL Date Functions

Date functions are used to manipulate or perform operation on date values.

MySQL Date Functions

The following table summarizes some most important MySQL's built-in date functions:

Function	Description
`NOW()`	Returns the current date and time.
`CURDATE()`	Returns the current date.
`CURTIME()`	Returns the current time
`DATE()`	Extract the date part of a date or datetime expression.
`DAY()`	Returns the day of the month (0-31).
`DAYNAME()`	Returns the name of the weekday.
`MONTH()`	Returns the month from the date passed (1-12).
`MONTHNAME()`	Returns the name of the month.
`YEAR()`	Returns the year.
`DATE_FORMAT()`	Displays date and time value in other formats.
`EXTRACT()`	Extract part of a date.
`DATE_ADD()`	Adds a specified time value (or interval) to a date value.
`DATE_SUB()`	Subtracts a specified time value (or interval) from a date value.
`DATEDIFF()`	Returns the number of days between two dates

SQL Server Date Functions

The following table summarizes some most important SQL Server's built-in date functions:

Function	Description
`GETDATE()`	Returns the current date and time.
`DATEPART()`	Returns the specified datepart of the specified date e.g. `DATEPART(year,'2016-10-25')` return 2016.
`DAY()`	Returns the day of the month (0-31).
`MONTH()`	Returns the month from the specified date (0-12).
`YEAR()`	Returns the year from the specified date.
`DATEADD()`	Adds or subtracts a specified time interval from a date.
`DATEDIFF()`	Returns the date or time between two specified dates.
`CONVERT()`	Displays date and time value in other formats.