SQL functions are built-in operations that can be used to perform calculations and data manipulation.

SQL functions are typically used in the SELECT statement to transform data values in a specific way

SQL functions can be used to perform mathematical operations such as addition, subtraction

A user can also write his function and use it is SQL statement.

User-defined functions can be used to perform operations that are not available in the built-in functions

SQL functions can be nested, allowing multiple functions to be used together.

SQL functions can also be used to convert data from one type to another.

SQL functions can impact query performance, so it's important to use them correctly and optimize their use when possible.