Reputation: 859
I have the table 'meta_data' with the following fields:
I'd like to loop through and display a list of EACH post (post_id
) that has an entry for meta_key='abc'
but not one for meta_key='def'
Basically, every post that has a meta_key='abc'
entry should have a meta_key='def'
entry. I want to generate the list so I can add the missing meta_key='def'
entries.
Upvotes: 19
Views: 43498
Reputation: 9389
To achieve this you should use the LEFT OUTER JOIN operation joining the same table.
SELECT a.*
FROM meta_data a
LEFT OUTER JOIN meta_data b ON a.post_id = b.post_id AND b.meta_value = 'def'
WHERE
a.meta_value = 'abc'
AND b.post_id IS null
Upvotes: 25
Reputation: 425448
Make an outer (left) join to itself, filtering on those records that don't match by looking for rows with a null id in the joined table:
select t1.*
from meta_data t1
left join meta_data t2 on t2.post_id = t1.post_id and t2.meta_key='def'
where t1.meta_key='abc'
and t2.id is null
Upvotes: 11