动态sql语句基本语法

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


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 (' tableNameselect ' + @fname + ' from') --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 + 'fromtableName'


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 tableName'


Exec(@s) --成功


exec sp_executesql @s --此句正确



eg:


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 = ' = count(*) from tableNameselect @a'


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


select @num

eg: