1:
普通SQL語句可以用Exec執(zhí)行
eg:   Select * from tableName
      Exec(‘select * from tableName‘)
      sp_executesql N‘select * from tableName‘    -- 請注意字符串前一定要加N

2:
字段名，表名，數(shù)據(jù)庫名之類作為變量時，必須用動態(tài)SQL
eg:  
declare @fname varchar(20)
set @fname = ‘[name]‘
Select @fname from sysobjects                     -- 錯誤
Exec(‘select ‘ + @fname + ‘ from sysobjects‘)     -- 請注意 加號前后的 單引號的邊上要加空格
exec sp_executesql N‘ select ‘ + @fname + ‘ from sysobjects‘
當然將字符串改成變量的形式也可
    declare @s varchar(1000)
    set @s = ‘select ‘ + @fname + ‘ from sysobjects‘
    Exec(@s)                -- 成功
    exec sp_executesql @s   -- 此句會報錯

    declare @s Nvarchar(1000)  -- 注意此處改為nvarchar(1000)
    set @s = ‘select ‘ + @fname + ‘ from sysobjects‘
    Exec(@s)                -- 成功   
    exec sp_executesql @s   -- 此句正確，

3: 輸出參數(shù)
eg:
declare @num,
        @sqls
set @sqls=‘select count(*) from  ‘ + @servername + ‘.a.dbo.b‘
exec(@sqls)
我如何能將exec執(zhí)行的結果存入變量@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