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Checking Two Tables For Matching Records


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#1 c_pattle

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Posted 13 December 2012 - 10:55 AM

I was just wondering if anyone knows what the most efficient way of checking to see if two tables contain matching records.

So for example I have a table called 'orders' which have a primary key of order_id.

Then I have a table called 'order_comments' which also has a field called order_id and I want to run a query that will check which orders don't have entries in order_comments.

Thanks for any help

#2 Barand

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Posted 13 December 2012 - 12:28 PM

SELECT o.order_id
FROM orders o
LEFT JOIN order_comments c USING (order_id)
WHERE c.order_id IS NULL

Edited by Barand, 13 December 2012 - 12:28 PM.

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