From http://www.w3schools.com (Copyright Refsnes Data)

SQL Functions

SQL has many built-in functions for performing calculations on data.

SQL Aggregate Functions

SQL aggregate functions return a single value, calculated from values in a column.

Useful aggregate functions:

• AVG() - Returns the average value
• COUNT() - Returns the number of rows
• FIRST() - Returns the first value
• LAST() - Returns the last value
• MAX() - Returns the largest value
• MIN() - Returns the smallest value
• SUM() - Returns the sum

SQL Scalar functions

SQL scalar functions return a single value, based on the input value.

Useful scalar functions:

• UCASE() - Converts a field to upper case
• LCASE() - Converts a field to lower case
• MID() - Extract characters from a text field
• LEN() - Returns the length of a text field
• ROUND() - Rounds a numeric field to the number of decimals specified
• NOW() - Returns the current system date and time
• FORMAT() - Formats how a field is to be displayed

Tip: The aggregate functions and the scalar functions will be explained in details in the next chapters.

From http://www.w3schools.com (Copyright Refsnes Data)