Mysql PHP query updation

I have a two tables cstomers and orders table. These tables contain 20,000 records

What i need is i want to update the orders table with the customer_id based on the email. Can i use subquery and php OR it can be accomplished using a single query and efficient method?

customers table

id  email     name
--------------
1 | email1 | name1
2 | email2 | name3
3 | email3 | name3

Orders table

order_id  customer_id   email    product name  group_id
-------------- -----------------------------------------
1         1             email1    prod1          0
2         (NULL)        email1    prod1          1
3         1             email1    prod1     开发者_如何学运维     0
4         (NULL)        email2    prod1          1
5         2             email2    prod1          0
6         2             email2    prod1          1
7         (NULL)        email2    prod1          1
2         (NULL)        email1    prod1          1

• group_id =0 means that the customer has account
• group_id =1 means that the customer does not have account

UPDATE customers c INNER JOIN orders o ON o.customer_id = c.id
SET o.customer_id = c.id
WHERE o.email = c.email

That should do it. Because this is an INNER JOIN, it just won't update orders for user accounts that don't exist in the customers table.

Maybe this (untested)

UPDATE orders o SET o.customer_id = (SELECT c.customer_id FROM customers c WHERE c.email = o.email)