How can I merge the columns from two tables into one output?

Question

I have two tables with similar information. Let\'s call them items_a and items_b. They should be one, but they are coming from different sources, s

Answer 1

I had a similar problem with a small difference: some a.category_id are not in b and some b.category_id are not in a.
To solve this problem just adapt the excelent answer from beny23 to

select a.col1, b.col2, a.col3, b.col4, a.category_id 
from items_a a
LEFT OUTER JOIN
items_b b 
on a.category_id = b.category_id

Hope this helps someone.
Regards.