SQL -- 简单语句学习总结7条

--if object_id('guestbook') is  null

--CREATE TABLE guestbook (id int PRIMARY KEY, visitor VARCHAR(40),comments TEXT,entrydate DATETIME)

--insert into guestbook values(3,'a','123','2016-05-12')

--insert into guestbook values(4,'a','1234','2016-05-12')

--insert into guestbook values(5,'a','12345','2016-05-12')

--if object_id('guestbook') is not null

--drop table guestbook

--if exists(select * from sysobjects where name='guestbook')

--drop table guestbook

--update guestbook set visitor='b' where id='4'

--select * from guestbook

--delete guestbook where id='3'

--truncate table guestbook