SQL functions are simple code snippets that are frequently used and re-used in database systems for data processing and manipulation. Functions are the measured values. It always performs a specific task. The following rules should be remembered while creating functions:
A function should have a name, and the name cannot begin with a special character such as @, $, #, or other similar characters.
Functions can only work with the SELECT statements.
Every time a function is called, it compiles.
Functions must return value or result.
Functions are always used with input parameters.
SQL categories the functions into two types:
User-Defined Function: Functions created by a user based on their needs are termed user-defined functions.
System Defined Function: Functions whose definition is defined by the system are termed system-defined functions. They are built-in database functions.
SQL functions are used for the following purposes:
To perform calculations on data
To modify individual data items
To manipulate the output
To format dates and numbers
To convert data types
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