1:普通SQL語句可以用Exec執行
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,數據庫名之類作爲變量時,必須用動態SQL
eg:
declare @fname varchar(20)
set @fname = '[name]'
Select @fname from sysobjects -- 錯誤
Exec('select ' + @fname + ' from sysobjects') -- 請注意 加號前後的 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) -- 注意此處改爲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
eg:
declare @num,
@sqls
set @sqls='select count(*) from ' + @servername + '.a.dbo.b'
exec(@sqls)
我如何能將exec執行的結果存入變量@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