Something like this ?
SELECT Building_code, Sum(IIf(tn='T1',1,0)) AS Table1Ct, Sum(IIf(tn='T2',1,0)) AS Table2Ct, (Sum(IIf(tn='T2',1,0)) - Sum(IIf(tn='T1',1,0))) AS [Variance]
FROM (
SELECT Building_code, 'T1' AS tn FROM Table1
UNION ALL SELECT Building_code, 'T2' FROM Table2
) AS U
GROUP BY Building_code;
Hope This Helps, PH.
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