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SQL has many built-in functions that allow you to perform calculations on data.
SQL aggregate functions perform calculations on a set of values and return a single value. The following table summarizes some useful aggregate functions:
| Function | Description |
|---|---|
| AVG() | Return the average value of values |
| SUM() | Return the sum of values |
| COUNT() | Return the number of rows in the result set |
| MAX() | Return the maximum value |
| MIN() | Return the minimum value |
SQL string functions perform operations on string input values and then return a string or numeric value. The following table summarizes some useful string functions:
| Function | Description |
|---|---|
| CONCAT() | Return a string by concatenating two or more string values. |
| CONCAT_WS() | Return a string by concatenating two or more string values using a delimiter. |
| FORMAT() | Return a value formatted in a specified format. |
| LOWER() | Convert a string to lowercase. |
| UPPER() | Convert a string to uppercase. |
| TRIM() | Remove leading and trailing spaces from a string. |
| REVERSE() | Return the reverse order of a string value. |
| SUBSTRING() | Return a substring from a string. |
Date functions are used to perform operations on date values or execute operations.
The following table summarizes some of the most important MySQL built-in date functions:
| Function | Description |
|---|---|
| NOW() | Return the current date and time. |
| CURDATE() | Return the current date. |
| CURTIME() | Return the current time |
| DATE() | Extract the date part from a date or datetime expression. |
| DAY() | Return the day of the month (0-31) |
| DAYNAME() | Return the name of the day of the week. |
| MONTH() | Return the date after a certain number of days.1-12The month of)。 |
| MONTHNAME() | Return the name of the month. |
| YEAR() | Return the year. |
| DATE_FORMAT() | Display date and time values in other formats. |
| EXTRACT() | Extract a part of the date. |
| DATE_ADD() | Add a specified time value (or interval) to a date value. |
| DATE_SUB() | Subtract a specified time value (or interval) from a date value. |
| DATEDIFF() | Return the number of days between two dates |
Note:These functions return the date and time of the computer running the database server instance.
The following table summarizes some of the most important SQL Server built-in date functions:
| Function | Description |
|---|---|
| GETDATE() | Return the current date and time. |
| DATEPART() | Return the specified date part of a specified date, for example DATEPART(year,'2016-10-25Return2016). |
| DAY() | Return the day of the month (0-31) |
| MONTH() | Return the month from a specified date (0-12The month starting with |
| YEAR() | Return the year of a specified date. |
| DATEADD() | Add or subtract a specified time interval from a date. |
| DATEDIFF() | Return the date or time between two specified dates. |
| CONVERT() | Display date and time values in other formats. |