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MySQL constraint_ Primary key constraint primary key

2022-07-22 17:27:00 【Camellia——】

-- Primary key constraint primary key（ characteristic not null+unqiue） Non empty and unique
-- Primary key constraints apply to non business fields ： Number id
-- Add a primary key when creating a table
CREATE TABLE stu(
id INT PRIMARY KEY, -- Primary key
NAME VARCHAR(20)
);
-- insert data
INSERT INTO stu(id,NAME)VALUES(1,' Zhang San '),(2,' Li Si ');
-- Delete primary key drop PRIMARY KEY: Can be repeated but still cannot be empty ,not null Constraints will not repeat with the deletion of the primary key
ALTER TABLE stu DROP PRIMARY KEY;

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