动态SQL语句

1:

普通SQL语句可以用Exec执行

eg: Select * from tableName

Exec('select * from tableName')

sp_executesql N'select * from tableName' -- 请注意字符串前一定要加N

2:

字段名，表名，数据库名之类作为变量时，必须用动态SQL

eg:

declare @fname varchar(20)

set @fname = '[name]'

Select @fname from sysobjects -- 错误

Exec('select ' + @fname + ' from sysobjects') -- 请注意 加号前后的 单引号的边上要加空格

exec sp_executesql N' select ' + @fname + ' from sysobjects'

当然将字符串改成变量的形式也可

declare @s varchar(1000)

set @s = 'select ' + @fname + ' from sysobjects'

Exec(@s) -- 成功

exec sp_executesql @s -- 此句会报错

declare @s Nvarchar(1000) -- 注意此处改为nvarchar(1000)

set @s = 'select ' + @fname + ' from sysobjects'

Exec(@s) -- 成功

exec sp_executesql @s -- 此句正确，

3: 输出参数

eg:

declare @num,

@sqls

set @sqls='select count(*) from ' + @servername + '.a.dbo.b'

exec(@sqls)

我如何能将exec执行的结果存入变量@num中

declare @num int,

@sqls nvarchar(4000)

set @sqls='select @a=count(*) from '+@servername+'.a.dbo.b'

exec sp_executesql @sqls,N'@a int output',@num output

select @num