SQL如何创建和删除主键

1、创建主键：新建表时直接创建主键CREATE TABLE table_test( id INT NOT NULL, name VARCHAR(20) NOT NULL, address VARCHAR(20), PRIMARY KEY(id));

3、创建复合键：新建表时创建复合键（主键字段不能包含NULL）。CREATE TABLE table_t髫潋啜缅est( user_id INT NOT NULL, user_name VARCHAR(20) NOT NULL, user_address VARCHAR(20), PRIMARY KEY (user_id, user_name));

5、删除主键ALTER TABLE table_test DROP PRIMARY KEY ;