简单问题，变量可否做表名？？
declare @tablename char(10)
set @tablename= 'test '
select * from @tablename
最后一行报语法错
到底怎么错了？帮忙看看
[解决办法]
--变量不能作为表名
declare @tablename char(10)
set @tablename= 'test '
exec( 'select * from '+@tablename)
[解决办法]
declare @tablename char(10),@sql varchar(8000)
set @tablename= 'test '
set @sql= 'select * from '+@tablename
exec(@sql)
[解决办法]
declare @tablename char(10)
set @tablename= 'test '
select @tablename
[解决办法]
--要用动态sql
create table #a (id int,username nvarchar(10),valid nvarchar(1),create_date datetime)
insert into #a (id,username,valid,create_date)
select 1, 'admin ', 'y ', '2007-3-1 ' union
select 2, 'yy ', 'y ', '2007-3-1 ' union
select 3, 'abc ', 'n ', '2007-3-3 ' union
select 4, 'ddd ', 'y ', '2007-3-1 ' union
select 5, 'sdf ', 'y ', '2007-3-4 ' union
select 6, 'love ', 'n ', '2007-3-1 ' union
select 7, 'like ', 'n ', '2007-3-6 ' union
select 8, 'good ', 'y ', '2007-3-1 '
declare @name varchar(100)
declare @str varchar(100)
set @name= '#a '
set @str= 'select * from ' + @name
exec(@str)
[解决办法]
--try
declare @tablename char(10)
set @tablename= 'test '
exec( 'select * from '+@tablename)
[解决办法]
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
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
