Question

I am really not good at sql, The problem is the following:
I have a metadata table like this

META:
id(pk)  prop1   prop2
     1  'pr1'   'pr2'
     2  'pr1'   'pr2'

At the same time, I have many child tables which look something like this:

TABLE1:
metaID(fk-pk)   indx(pk)    active  ...
            1          1         1  ...
            1          2         0  ...
            1          3         1  ...
            2          1         1  ...

and a second table similar to the first

TABLE2:
metaID(fk-pk)   indx(pk)    active  ...
            1          1         1  ...
            1          2         1  ...
            2          1         0  ...
            2          2         0  ...

I need a query which retrieves the the metadata table properties and the number of records in each child table which are active.

For example if I want the elements with prop1 = 'pr1 the query should answer:

meta-id prop1   prop2   TAB1CNT TAB2CNT
      1 'pr1'   'pr2'         2       2
      2 'pr1'   'pr2'         1       0

where TAB1CNT is the count of the active elements of TABLE1 and the same goes for TAB2CNT

Answer 1

Something like this should do the trick. This would return all meta records, regardless of if there were any active records in table1 or table2.

SELECT ID, prop1, prop2, ISNULL(t1.ActiveCount, 0) AS TAB1CNT, ISNULL(t2.ActiveCount, 0) AS TAB2CNT
FROM META m
    LEFT JOIN
    (
        SELECT metaID, COUNT(*) AS ActiveCount
        FROM TABLE1
        WHERE active = 1
        GROUP BY metaID
    ) t1 ON m.ID = t1.metaID
    LEFT JOIN
    (
        SELECT metaID, COUNT(*) AS ActiveCount
        FROM TABLE2
        WHERE active = 1
        GROUP BY metaID
    ) t2 ON m.ID = t2.metaID

Hopefully from this, you can then add whatever clauses you want to return only the META records you are interested in.