MySQL Join three tables, two of them with additional condition

Question

I have to left join one table (bonds) with two other tables (orders_bid, orders_ask). But both other tables must also have a condition between them (customer_id must be the same).

bonds
-----------
id
ticker

...

orders_bid
-----------
id
bonds_id
customer_id
price

...

orders_ask
-----------
id
bonds_id 
customer_id 
price

My approach is the following:

SELECT bonds.ticker, orders_bid.price, orders_ask.price FROM bonds
LEFT JOIN orders_bid ON bonds.id=orders_bid.bonds_id
LEFT JOIN orders_ask ON bonds.id=orders_ask.bonds_id

But this leads to result rows are getting mixed over different customers, as the customer_id is not respected between both joined tables. Something like...

WHERE orders_bid.customer_id=orders_aks.customer_id

...is additionally needed, but it must not be a WHERE statement as something like an outer join is needed (one side might be empty). What's the right way?

Answer 1

Try by adding it to the JOIN conditions.

SELECT    bonds.ticker, orders_bid.price, orders_ask.price FROM bonds
LEFT JOIN orders_bid 
ON        bonds.id = orders_bid.bonds_id
LEFT JOIN orders_ask 
ON        bonds.id = orders_ask.bonds_id
AND       orders_bid.customer_id = orders_ask.customer_id