关于if exists的用法及说明分析

if exists (select * from sys.databases where name = '数据库名')  
  drop database [数据库名]

if exists (select * from sysobjects where id = object_id(N'[表名]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)  
  drop table [表名]

if exists (select * from sysobjects where id = object_id(N'[存储过程名]') and OBJECTPROPERTY(id, N'IsProcedure') = 1)  
  drop procedure [存储过程名]

if object_id('tempdb..#临时表名') is not null    
  drop table #临时表名

--SQL Server 2000   
IF EXISTS (SELECT * FROM sysviews WHERE object_id = '[dbo].[视图名]'  
--SQL Server 2005   
IF EXISTS (SELECT * FROM sys.views WHERE object_id = '[dbo].[视图名]'  --SQL Server 2000
IF EXISTS (SELECT * FROM sysviews WHERE object_id = '[dbo].[视图名]'
--SQL Server 2005
IF EXISTS (SELECT * FROM sys.views WHERE object_id = '[dbo].[视图名]'

--  判断要创建的函数名是否存在    
  if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[函数名]') and xtype in (N'FN', N'IF', N'TF'))    
  drop function [dbo].[函数名]    --  判断要创建的函数名是否存在  

SELECT [name],[id],crdate FROM sysobjects where xtype='U'  
/*  
xtype 的表示参数类型，通常包括如下这些  
C = CHECK 约束  
D = 默认值或 DEFAULT 约束  
F = FOREIGN KEY 约束  
L = 日志  
FN = 标量函数  
IF = 内嵌表函数  
P = 存储过程  
PK = PRIMARY KEY 约束（类型是 K）  
RF = 复制筛选存储过程  
S = 系统表  
TF = 表函数  
TR = 触发器  
U = 用户表  
UQ = UNIQUE 约束（类型是 K）  
V = 视图  
X = 扩展存储过程*/

if exists(select * from syscolumns where id=object_id('表名') and name='列名')  
  alter table 表名 drop column 列名

if columnproperty(object_id('table'),'col','IsIdentity')=1  
  print '自增列'  
else  
  print '不是自增列'  

if exists(select * from sysindexes where id=object_id('表名') and name='索引名')    
  print  '存在'    
else    
  print  '不存在11 查看数据库中对象
SELECT * FROM sys.sysobjects WHERE name='对象名'