T-SQL朝花夕拾(五) 动态T-SQL语句语法

-- 方法1查询表改为动态
select * from sysobjects
exec ( ' select ID,Name from sysobjects ' )
exec sp_executesql N ' select ID,Name from sysobjects ' -- 多了一个N为unicode

-- 方法2:字段名，表名，数据库名之类作为变量时,用动态SQL
declare @FName varchar ( 20 )
set @FName = ' ID '
exec ( ' select ' + @FName + ' from sysobjects where ' + @FName + ' =5 ' )


declare @s varchar ( 1000 )
set @s = N ' select ' + @FName + ' from sysobjects where ' + @FName + ' =5 '
exec sp_executesql @s -- 会报错


declare @s nvarchar ( 1000 ) -- 改为nvarchar
set @s = N ' select ' + @FName + ' from sysobjects where ' + @FName + ' =5 '
exec sp_executesql @s -- 成功


-- 方法3:输入参数

declare @i int , @s nvarchar ( 1000 )
set @i = 5
exec ( ' select ID,Name from sysobjects where ID= ' + @i )

set @s = ' select ID,Name from sysobjects where ID=@i '
exec sp_executesql @s ,N ' @i int ' , @i -- 此处输入参数要加上N

-- 方法4:输出参数

declare @i int , @s nvarchar ( 1000 )
set @s = ' select @i=count(1) from sysobjects '

-- 用exec
exec ( ' declare @i int ' + @s + ' select @i ' ) -- 把整个语句用字符串加起来执行

-- 用sp_executesql
exec sp_executesql @s ,N ' @i int output ' , @i output -- 此处输出参数要加上N
select @i


-- 方法5:输入输出

-- 用sp_executesql
declare @i int , @con int , @s nvarchar ( 1000 )
set @i = 5
select @s = ' select @con=count(1) from sysobjects where ID>@i '
exec sp_executesql @s ,N ' @con int output,@i int ' , @con output , @i
select @con

-- 用exec
declare @i int , @s nvarchar ( 1000 )
set @i = 5
select @s = ' declare @con int select @con=count(1) from sysobjects where ID> ' + rtrim ( @i ) + ' select @con '
exec ( @s )