STUFF FUNCTION

This function inserts a string into another string, it deletes a specified lenght of the characters at the starting position in the expression and inserts the second string at the starting position.

syntax : STUFF ( character_expression , start , length , replaceWith_expression )

start : Integer value it specifies the position to start the insertion.

length : Integer value it specifies the number of characters to delete from start position.

Reference : MSDN_STUFF



Difference between STUFF and REPLACE Functions :

STUFF function deletes a specified length of string from start position and inserts the second string in the expression.

REPLACE function replaces all occurences of the string with the second string in the expression.

Check this code

select stuff('krishna',1,0,'MR. ')

output is
MR. krishna

select replace('krishna', 'k','satya k')

output is
satya krishna