Question

How to write this MySQL update statement:

table1
identity

table2
memberid, username, email

Some values in identity of table1 are email, some are username, how to replace the values in identity of table1 with the corresponding value of memberid of table2?

Answer 1

UPDATE table1, table2
SET table1.indentity = table2.memberid 
WHERE table1.FOREIGNKEYHERE = table2.PRIMARYKEYHERE;