--計算列的另類用法
CREATE TABLE t2
(a int, b int, c int, x float,
y AS CASE x
WHEN 0 THEN a
WHEN 1 THEN b
ELSE c
END)
INSERT INTO [t2] ([a], [b], [c], [x])
VALUES (1, 2, 3, 0)
GO
INSERT INTO [t2] ([a], [b], [c], [x])
VALUES (2, 3, 4, 1)
GO
INSERT INTO [t2] ([a], [b], [c], [x])
VALUES (3, 4, 5, 0)
GO
select * from t2
a b c x y
----------------------------------
1 2 3 0.0 1
2 3 4 1.0 3
3 4 5 0.0 3