-- 新增学生表 student IF object_id(‘student‘) IS NOT NULL DROP TABLE student; CREATE TABLE student ( id bigint NOT NULL IDENTITY(1,1) , name nvarchar(40) NULL , xb nvarchar(40) NULL , age int(3) NULL , birthday datetime NULL , className nvarchar(80) NULL ); ALTER TABLE student ADD PRIMARY KEY (ID); -- 学生表新增班级 className 字段 IF NOT EXISTS(SELECT 1 FROM sys.columns WHERE name=‘className‘ AND object_id=object_id(‘student‘)) alter table student add className nvarchar(40); ELSE alter table student alter column className nvarchar(20);