What is the purpose of the SQL Server substring function?

The SUBSTRING function in SQL Server is used to extract a portion of a given string. It allows you to retrieve a substring from the original string based on a specified starting position and length. The SUBSTRING function is commonly used to extract a part of a string to meet specific requirements or for data processing purposes.

The syntax for the SUBSTRING function is as follows:
SUBSTRING(string, start, length)

Explanation of parameters:

1. String: the original string to be truncated.
2. Starting position: Indicating the position in the original string where to begin extracting the substring, with counting starting from 1.
3. Length: an optional parameter indicating the length of the substring to be trimmed. If not specified, all characters from the starting position to the end of the string will be trimmed.

The following functions can be achieved by using the SUBSTRING function:

1. Extract a portion of a string, such as extracting the last name from a name or the year from a date string.
2. Cut or shorten strings based on specific requirements for further processing and operations.
3. Process and transform strings, such as converting strings in a specific format to another format.

In conclusion, the SUBSTRING function in SQL Server is used to extract a part of a string in order to meet specific requirements or perform data processing.