how would i merge a column where matches a different column? It's very similar to the below post

How to merge column in mysql depending on match   

table user



I would like to Merge customer_id from table user to table cust where customers_firstname AND customers_name match

table cust
You need to apply update with join if you want to update the cust table

update cust c 
join user u on u.customers_firstname = c.customers_firstname
and u.customers_lastname = c.customers_lastname
set c.customers_id = u.customers_id