Both STUFF and REPLACE are used to replace characters in a string.

select replace('abcdef','ab','xx') results in xxcdef

select replace('defdefdef','def','abc') results in abcabcabc

We cannot replace a specific occurrence of “def” using REPLACE.

select stuff('defdefdef',4, 3,'abc') results in defabcdef

where 4 is the character to begin replace from and 3 is the number of characters to replace.