这样的sql语句为什么错了？？

[geniusqing]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
set @s=@s+'union'
select @s
exec(@s)
错误! 又问怎样得到下面的两句

select fdesc from fcDepartment unoin
select fdesc from fcDepartment unoin
能得到结果

[子陌红尘]

unoin 哪个查询？

[OracleRoob]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
set @s=@s+'union'
select @s
exec(@s)

错误!
-----------------------------
select fdesc from fcDepartment union --只有一个Select语句，不需要用union

[-狙击手-]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
--set @s=@s+'union'
select @s
exec(@s)

[mislrb]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
set @s=@s+'union'+@s
exec(@s)

[OracleRoob]

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

[QQMagicer]

搂主的语法有问题,至少最后一个union是不正确的

[geniusqing]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
set @s=@s+'union'+@s
exec(@s)
不能执行阿，因为 select @s为这个
select fdesc from fcDepartment unionselect fdesc from fcDepartment

[-狙击手-]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
set @s=@s+' union '+@s
exec(@s)

---

select fdesc from fcDepartment union select fdesc from fcDepartment

[OracleRoob]

declare @s varchar(8000)
set @s='select fdesc from fcDepartment '
set @s=@s+' union '+@s
exec(@s)

--union 两边都要有空格

[Comer]

select fdesc from fcDepartment unionselect fdesc from fcDepartment

明显是缺个空格，怎么自己不动动脑筋呢、

[wazh]

--应该这样才对啊

select fdesc from fcDepartment union select fdesc from fcDepartment


--union两边都要有空格语法才对