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DROP TABLE IF EXISTS stuinfo;CREATE TABLE stuinfoid INT,stuName VARCHAR20,gender CHAR1,seat INT,age INT,majorid INT;# 添加非空约束ALTER TABLE stuinfo MODIFY COLUMN st......

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列级约束案例：CREATE TABLE majorid INT PRIMARY key,majorName VARCHAR20;CREATE TABLE stuinfoid INT PRIMARY key,stuName VARCHAR20 NOT NULL,gender CHAR1,seat INT UNIQUE,a......