MySQL Join Same Table

Question

I have the table \'meta_data\' with the following fields:

• id
• post_id
• meta_key
• meta_value

I\'d like to loop throug

Answer 1

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