如果表1中存在值，则插入表2 mysql

Question

For my ordering system, when an admin inserts an order i need to check if the customer he inserts for the order exists in my customer table.
Im trying something like this, but with no luck..

$sql = "IF EXISTS(SELECT * FROM customer WHERE customer_id = '$customer')
THEN insert into `order` (customer_id, product, quantity, creation_time, order_note, order_employee)
values ('$customer', '$product', '$quantity', 'now()', '$note', '$employee')";

Error: syntax error in first line. What is wrong here?
And is this the right approach? Is there a better way?

Answer 1

you might want to do it "backwards" - insert if exists:

$sql = "insert into `order` (customer_id, product, quantity, creation_time, order_note, order_employee)
select '$customer', '$product', '$quantity', now(), '$note', '$employee'
from dual
where EXISTS(SELECT * FROM customer WHERE customer_id = '$customer')";