if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[PerPer
2017-03-10 10:02
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这句话是什么意思?if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[PerPer请问:if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[PerPersonData]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)中的object_id(N'[dbo].[PerPersonData]')是什么意思?那个object_id函数?那个N?还有OBJECTPROPERTY(id, N'IsUserTable') = 1中的OBJECTPROPERTY函数是什么意思?那个=1又是什么意思?OBJECT_ID:返回数据库对象标识号。N是显式的将非unicode字符转成unicode字符,它来自SQL-92 标准中的 National(Unicode)数据类型,用于扩展和标准化,在这里可以不用,写作object_id(PerPersonData)。OBJECTPROPERTY:返回当前数据库中对象的有关信息。1表“真”。同样可以写成OBJECTPROPERTY(id, sUserTable) = 1。整条语句的意思是判断数据库里有没有存在PerPersonData这样一张表。整条语句可以简写成:if exists (select * from sysobjects where objectproperty(object_id('PerPersonData'),'istable') = 1)--------------------------------------------------------------------------------------------------------if exists(select * from dbo.sysobjects where id = object_id(N'[dbo].[部门班级表]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)drop table [dbo].[部门班级表] -----这句SQL语句是什么意思啊??
object_id是系统自带的,用于获取对象ID的函数。N的意思是强制转换成Nvarchar,单引号里的内容就是表名。 OBJECTPROPERTY也是系统自动的函数,根据ID来判断是对象的类型,有可能是系统表、用户表、存储过程、函数等。IsUserTable表示是用户建立的表。IsProcedure表示存储过程OBJECT_ID:返回数据库对象标识号。N是显式的将非unicode字符转成unicode字符,它来自 SQL-92 标准中的 National(Unicode)数据类型,用于扩展和标准化,在这里可以不用,写作object_id(PerPersonData)。OBJECTPROPERTY:返回当前数据库中对象的有关信息。1表“真”。同样可以写成OBJECTPROPERTY(id, sUserTable) = 1。整条语句的意思是判断数据库里有没有存在PerPersonData这样一张表,是否用户创建的表
参考知识库
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