1) 先变量再字段
SET NOCOUNT ON;
DECLARE @i INT, @j INT
DECLARE @Table TABLE
(
Id1 INT,
Id2 INT
);
INSERT @Table(Id1, Id2)
SELECT 1, 10
UNION ALL
SELECT 2, 20
UNION ALL
SELECT 3, 30;
SELECT @i = 1, @j = 0
UPDATE @Table SET Id1 = @i, Id2 = Id1, @i = @i + 1
SELECT * FROM @Table
SELECT @i = 1, @j = 0
UPDATE @Table SET Id1 = @i, Id2 = @j, @j = @i + 10, @i = @i + 1
SELECT * FROM @Table
SET NOCOUNT OFF;
结果:
Id1 Id2
----------- -----------
2 1
3 2
4 3
Id1 Id2
----------- -----------
2 11
3 12
4 13
2) 变量之间, 从左到右
SET NOCOUNT ON;
DECLARE @i INT, @j INT
DECLARE @Table TABLE
(
Id1 INT,
Id2 INT
);
INSERT @Table(Id1, Id2)
SELECT 1, 10;
SELECT @i = 1, @j = 0
UPDATE @Table SET @j = @i, @i = @i + 1
PRINT '@i = ' + CAST(@i AS VARCHAR) + ', @j = ' + CAST(@j AS VARCHAR)
SELECT @i = 1, @j = 0
UPDATE @Table SET @i = @i + 1, @j = @i
PRINT '@i = ' + CAST(@i AS VARCHAR) + ', @j = ' + CAST(@j AS VARCHAR)
SELECT @i = 1, @j = 0
UPDATE @Table SET @i = @j + 1, @j = @i
PRINT '@i = ' + CAST(@i AS VARCHAR) + ', @j = ' + CAST(@j AS VARCHAR)
SELECT @i = 1, @j = 0
UPDATE @Table SET @i = @j, @j = @i
PRINT '@i = ' + CAST(@i AS VARCHAR) + ', @j = ' + CAST(@j AS VARCHAR)
SET NOCOUNT OFF;
结果:
@i = 2, @j = 1
@i = 2, @j = 2
@i = 1, @j = 1
@i = 0, @j = 0
3) 字段之间, 并行执行
SET NOCOUNT ON;
DECLARE @Table TABLE
(
Id1 INT, Id2 INT
);
INSERT @Table(Id1, Id2)
SELECT 1, 10
UNION ALL
SELECT 2, 20
UNION ALL
SELECT 3, 30;
UPDATE @Table SET Id1 = Id2, Id2 = Id1
SELECT * FROM @Table
SET NOCOUNT OFF;
结果:
Id1 Id2
----------- -----------
10 1
20 2
30 3
