以下的文章主要向大家讲述的是SQL Server UPDATE的正确赋值次序，主要包括第一先先变量再字段，第二变量之间, 从左到右的运行，等相关内容的描述，以下就是正文的主要内容的详细介绍。
SQL Server UPDATE的赋值次序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
SQL Server UPDATE的赋值次序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
SQL Server UPDATE的赋值次序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
以上的相关内容就是对SQL Server UPDATE的赋值次序的介绍，望你能有所收获。