STUFF (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
SQL analytics endpoint in Microsoft Fabric
Warehouse in Microsoft Fabric
The STUFF function inserts a string into another string. It deletes a specified length of characters in the first string at the start position and then inserts the second string into the first string at the start position.
Transact-SQL syntax conventions
Syntax
STUFF ( character_expression , start , length , replace_with_expression )
Arguments
character_expression
An expression of character data. character_expression can be a constant, variable, or column of either character or binary data.
start
An integer value that specifies the location to start deletion and insertion. If start is negative or zero, a null string is returned. If start is longer than the first character_expression, a null string is returned. start can be of type bigint.
length
An integer that specifies the number of characters to delete. If length is negative, a null string is returned. If length is longer than the first character_expression, deletion occurs up to the last character in the last character_expression. If length is zero, insertion occurs at the start location, and no characters are deleted. length can be of type bigint.
replace_with_expression
An expression of character data. replace_with_expression can be a constant, variable, or column of either character or binary data. This expression replaces length characters of character_expression beginning at start. Providing NULL as the replace_with_expression, removes characters without inserting anything.
Return types
Returns character data if character_expression is one of the supported character data types. Returns binary data if character_expression is one of the supported binary data types.
Remarks
If the start position or the length is negative, or if the starting position is larger than length of the first string, a null string is returned. If the start position is 0, a null value is returned. If the length to delete is longer than the first string, it is deleted to the first character in the first string.
An error is raised if the resulting value is larger than the maximum supported by the return type.
Supplementary characters (surrogate pairs)
When using supplementary character (SC) collations, both character_expression and replace_with_expression can include surrogate pairs. The length parameter counts each surrogate in character_expression as a single character.
Examples
The following example returns a character string created by deleting three characters from the first string, abcdef, starting at position 2, at b, and inserting the second string at the deletion point.
SELECT STUFF('abcdef', 2, 3, 'ijklmn');
GO
Here's the result set.
---------
aijklmnef
(1 row(s) affected)