动态sql语句基本语法

动态sql语句基本语法
1 :普通SQL语句可以用Exec执行

eg: Select * from tableName
Exec('select * from tableName')
Exec 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 = 'FiledName'
Select @fname from tableName -- 错误,不会提示错误，但结果为固定值FiledName,并非所要。
Exec('select ' + @fname + ' from tableName') -- 请注意 加号前后的 单引号的边上加空格

当然将字符串改成变量的形式也可
declare @fname varchar(20)
set @fname = 'FiledName' --设置字段名

declare @s varchar(1000)
set @s = 'select ' + @fname + ' from tableName'
Exec(@s) -- 成功
exec sp_executesql @s -- 此句会报错 过程需要类型为 'ntext/nchar/nvarchar' 的参数 '@statement'。

declare @s Nvarchar(1000) -- 注意此处改为nvarchar(1000)
set @s = 'select ' + @fname + ' from tableName'
Exec(@s) -- 成功
exec sp_executesql @s -- 此句正确

3. 输出参数
declare @num int,
@sqls nvarchar(4000)
set @sqls='select count(*) from tableName'
exec(@sqls)
--如何将exec执行结果放入变量中？

declare @num int,
@sqls nvarchar(4000)
set @sqls='select @a=count(*) from tableName '
exec sp_executesql @sqls,N'@a int output',@num output
select @num

4、输出参数

declare @sql nvarchar(4000),
@TableName_History varchar(50),
@OutWellTime datetime,
@InWellTime datetime,
@Flag_History int, --历史表中的标记
@ID_History int, --历史表中的ID
@PersonID int
set @TableName_History='Data_History_2014_12'
set @PersonID=590
set @sql=N'select @ID_History=id,
@InWellTime=dt_InWellTime,
@OutWellTime=dt_OutWellTime,
@Flag_History=i_Flag
from ['+@TableName_History+']
where PersonID='+convert(varchar(20),@PersonID)

exec sp_executesql @sql,N'@ID_History int output,
@InWellTime datetime output,
@OutWellTime datetime output,
@Flag_History int output',
@ID_History output,@InWellTime output,
@OutWellTime output,@Flag_History output

--解释N'@ID_History int output' 定义输出参数，

@ID_History output 指定输出参数赋值给@ID_History

--查看结果
select @ID_History,@InWellTime,@OutWellTime,@Flag_History



5、exec sp_executesql 输入参数

declare @sql nvarchar(1000)
,@PersonID int
,@ClassID int
set @PersonID=6
set @ClassID=1
set @sql=N'select * from m_LampHistoryDataGet where personid=@PersonID and ClassID=@ClassID'
exec sp_executesql @sql,N'@PersonID int,@ClassID int',@PersonID,@ClassID