Chapter 7: SQL Functions

Mathematical functions

SQL has many mathematical functions that you can use in your queries. Here are a few:

• ABS() returns the absolute value of a number.
• ROUND() rounds a number to a specified number of decimal places.
• CEIL() returns the smallest integer greater than or equal to a number.
• FLOOR() returns the largest integer less than or equal to a number.
• POWER() returns a number raised to a specified power.

Date and time functions

SQL also has several functions for working with dates and times, including:

• NOW() returns the current date and time.
• DATE() extracts the date part of a datetime value.
• TIME() extracts the time part of a datetime value.
• YEAR() extracts the year from a date value.
• MONTH() extracts the month from a date value.
• DAY() extracts the day of the month from a date value.

String functions

For working with strings, SQL provides functions such as these:

• LENGTH() returns the length of a string.
• SUBSTRING() returns a portion of a string.
• CONCAT() concatenates two or more strings.
• UPPER() converts a string to uppercase.
• LOWER() converts a string to lowercase.

Aggregate functions

Aggregate functions perform calculations on groups of rows. For example:

• COUNT() counts the number of rows in a group.
• SUM() calculates the sum of a group of values.
• AVG() calculates the average of a group of values.
• MAX() returns the maximum value in a group.
• MIN() returns the minimum value in a group.