SQL的各種判斷

刪除帶約束(預設值)的表的某一列

--獲取字段上面的約束名稱,組合成一句字串,用exec執行

if exists(select  1 from sysobjects  where id in (select cdefault from syscolumns where name='[列名]' and  id=object_id('[表名]'))) 

begin
declare @name varchar(100) 
select  @name=name from sysobjects  where id in (select cdefault from syscolumns where name='[列名]' and  id=object_id('[表名]'))
exec ('alter table [表名] drop constraint '+@name) 
end--刪除列
if exists(select 1 from syscolumns where id=object_id('[表名]') and name='[列名]')
alter table [表名] drop column [列名]

--判斷某列是否存在預設值,不存在則新增預設值

if not  exists (select a.name as defaultname,b.name as tablename,* from sysobjects a
inner join sysobjects b on a.parent_obj = b.id
inner join syscolumns c on b.id=object_id('[表名]') and  c.name='[列名]'
where a.xtype = 'd' and b.xtype = 'u' and b.name = '[表名]')
alter table [表名]
add default (getdate()) for [列名]

判斷要建立的表名是否存在if exists (select * from dbo.sysobjects where id = object_id(n'[dbo].[表名]') and objectproperty(id, n'isusertable') = 1)

刪除表drop table [dbo].[表名]go

判斷要建立臨時表是否存在if object_id('tempdb.dbo.#test') is not nullbeginprint '存在'endelsebeginprint '不存在'end

判斷要建立的儲存過程名是否存在if exists (select * from dbo.sysobjects where id = object_id(n'[dbo].[儲存過程名]') and objectproperty(id, n'isprocedure') = 1)

刪除儲存過程drop procedure [dbo].[儲存過程名]go

判斷要建立的檢視名是否存在if exists (select * from dbo.sysobjects where id = object_id(n'[dbo].[檢視名]') and objectproperty(id, n'isview') = 1)

刪除檢視drop view [dbo].[檢視名]go

判斷要建立的函式名是否存在if exists (select * from dbo.sysobjects where id = object_id(n'[dbo].[函式名]') and xtype in (n'fn', n'if', n'tf'))

刪除函式drop function [dbo].[函式名]goif col_length('表名', '列名') is nullprint '不存在'if not exists(select 1 from syscolumns where name='列名' and id=object_id('表名'))

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