How to count tableA rows when joined to tableB

Question

In an Access database, TableA has a foreign key to TableB. TableB contains a column with four possible values. I need to count the number of rows in TableA for one of the four values in TableB. This was my initial attempt:

SELECT      COUNT(*) As TableACount 
FROM        TableA 
INNER JOIN  TableB ON TableA.fk_tableB = TableB.pk_tableB 
WHERE       TableB.[value] = 1

Here's another attempt:

SELECT      COUNT(*) As TableACount,
            TableB.[value]
FROM        TableA 
INNER JOIN  TableB ON TableA.fk_tableB = TableB.pk_tableB 
WHERE       TableB.[value] = 1
GROUP BY    TableB.[value]

The result returned in both queries appears to be the number of TableA rows times the number of TableB rows they are joined to. How can I get just the number of TableA rows?

Answer 1

You may either use a distinct count:

SELECT COUNT(DISTINCT a.pk_tableA) AS TableACount 
FROM TableA a
INNER JOIN TableB b
    ON a.fk_tableB = b.pk_tableB 
WHERE b.[value] = 1;

Or, use exists logic:

SELECT COUNT(*) AS TableACount
FROM TableA a
WHERE EXISTS (SELECT 1 FROM TableB b WHERE b.pk_tableA = a.fk_tableB AND b.[value] = 1);

Answer 2

SELECT      COUNT(*) As TableACount,
            TableA.fk_tableB
FROM        TableA 
INNER JOIN  TableB ON TableA.fk_tableB = TableB.pk_tableB 
WHERE       TableB.[value] = 1
GROUP BY    TableA.fk_tableB