如何在JOIN语句中使用CASE根据条件连接两个表？

Question

I have three tables : email, customer_new and customers_old. Now in email table there is a field called type that contains 0 or 1.
So if type contains 0 then I want to fetch name column from customer_new table else from customer_old table.

For this I made below mysql query :

SELECT email.*, 
CASE email.`type`
    WHEN 1 THEN customer_old.name
    ELSE customer_new.name
END AS customer_name 
LEFT JOIN 
CASE email.`type`
    WHEN 0 THEN customer_new ON email.customer_id = customer_new.id
    ELSE customer_old ON email.customer_id = customer_old.id
END
FROM email

Now when I run this query mysql always throws error.
Can somebody solve my issue regarding join two table through CASE statement based on condition ?

Thanks in advance.

Answer 1

Try with below query.

SELECT email . * , IF( email.type = '1', customer_old.name, customer_new.name ) AS name 
FROM email
LEFT JOIN customer_old ON ( customer_old.id = email.customer_id ) 
LEFT JOIN customer_new ON ( customer_new.id = email.customer_id )