Question

I have two (or three, or four…) tables which i want to select all at once to count the number of entries in all tables together.

for example if i have some tables:
‘news’, ‘articles’, ‘galleries’

in every table i have a row called like “author_id”

now, if i use following select statement:

SELECT *
FROM
news as n, articles as a, galleries as g
WHERE
n.author = 1
AND a.user = 1
AND g.uploader = 1

i only get a result if every table has at least one row with a author (or user or uploader whatever) matching ‘1’
how can i get a result even if one (or two..) tables do not contain ‘1’

Answer 1

Alternatively, you can combine the results of all table using UNION ALL in a subquery. Then you can now COUNT() the specified Author_ID. The following query will get the total number of records of a specified author_id in ALL tables.

SELECT COUNT(author_ID)
FROM
(
    SELECT userID AS Author_ID FROM news
    UNION ALL
    SELECT user_ID AS Author_ID FROM articles
    UNION ALL
    SELECT UiD AS Author_ID FROM galleries
) a
WHERE a.Author_ID = 1

followup question,

• how do you want the results to be shown? because this can also be solved by joining the tables.
• or what is the main table and the referencing table where you want to count the records?