这是判断表是否存在的if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[phone]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[phone]如果[phone]表 是变量如何 写,需要在储存过程中运行,请贴出语句
drop table [dbo].[phone]如果[phone]表 是变量如何 写,需要在储存过程中运行,请贴出语句
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
declare @sql nvarchar(4000)
set @tablename ='[phone]'
set @sql =('if exists (select * from dbo.sysobjects where id = object_id(N'''+@tablename+''') and OBJECTPROPERTY(id, N''IsUserTable'') = 1); drop table [dbo].'+@tablename +';')
exec (@sql)
drop table [dbo].[phone] 这如果是变量表名如何做,好像按规则改了下,老通不过,请贴下语句,
set @tb='dbo.tb'--tablename
set @sql='if exists (select * from dbo.sysobjects where id = object_id(N'''+@tb+''')
and OBJECTPROPERTY(id, N''IsUserTable'') = 1)
drop table '+@tb
exec(@sql)
declare @tableName varchar(30)
set @tableName='item'declare @strsql varchar(4000)
set @strsql='if exists (select * from dbo.sysobjects where id = object_id(N'+''''+'[dbo].['+@tableName+']'+''''+') and OBJECTPROPERTY(id, N'+''''+'IsUserTable'+''''+') = 1)' +' drop table [dbo].['+@tableName+']'
exec(@strsql)
declare @sql nvarchar(4000)
set @tablename ='[phone]'
set @sql =('if exists (select * from dbo.sysobjects where id = object_id(N'''+@tablename+''') and OBJECTPROPERTY(id, N''IsUserTable'') = 1); drop table [dbo].'+@tablename +';')
exec (@sql)===========================================
好像除掉
N''IsUserTable'') = 1);
+@tablename +';'
才能执行成功set @sqlstr =('if exists (select * from dbo.sysobjects where id = object_id(N'''+@tablename+''') and OBJECTPROPERTY(id, N''IsUserTable'') = 1) drop table [dbo].'+@tablename +'') print @sqlstr
exec (@sqlstr)语句中的'比较多,看的人比较乱,能按规则说下这样写的道理吗,理解才能记忆深刻,呵呵
请高手出招哦。
go
Declare @Table sysname
Set @Table='mytable'if exists (select * from dbo.sysobjects where id = object_id(@Table) and OBJECTPROPERTY(id, N'IsUserTable') = 1)
Exec (N'Drop table '+@Table)Exec (N'Create Table '+@Table+'(id int Identity(1,1) Primary Key ,x nvarchar(20))')Exec (N'Select * From '+@Table)
四个联系的引号在动态SQL里面即席成一个双引号.declare @tablename sysname
declare @sql nvarchar(4000)
set @tablename ='[phone]'
set @sql =('if exists (select * from dbo.sysobjects where id = object_id(N'''+@tablename+''')
and OBJECTPROPERTY(id, N''IsUserTable'') = 1);
drop table [dbo].'+@tablename +';')
exec (@sql)
------
这几处都是解析成单引号使用的,
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
declare @tablename sysname
declare @sql nvarchar(4000)
set @tablename ='[phone]'
set @sql =('if exists (select * from dbo.sysobjects where id = object_id(N'''+@tablename+''') and OBJECTPROPERTY(id, N''IsUserTable'') = 1); drop table [dbo].'+@tablename +';')
exec (@sql)