SELECT A.ID,A.FORMID,A.TOID=CASE
WHEN A.FORID=0 THEN B.BID
WHEN A.FORID>0 THEN C.CID
END
FROM A A
INNER JOIN B B
ON A.ID=B.ID
INNER JOIN C C
ON A.ID=C.ID
WHEN A.FORID=0 THEN B.BID
WHEN A.FORID>0 THEN C.CID
END
FROM A A
INNER JOIN B B
ON A.ID=B.ID
INNER JOIN C C
ON A.ID=C.ID
WHEN A.FORID=0 THEN B.BID
WHEN A.FORID>0 THEN C.CID
END
FROM A
LEFT INNER JOIN B
ON A.ID=B.ID
LEFT INNER JOIN C
ON A.ID=C.ID
WHEN A.FORID=0 THEN B.BID
WHEN A.FORID>0 THEN C.CID
END
FROM A
LEFT JOIN B
ON A.ID=B.ID
LEFT JOIN C
ON A.ID=C.ID
when Toid>0 then (select Bid from c where id=A.id ) end) from A