mysql PRIMARY KEY constraints

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Main (key) key (word)

mysql PRIMARY KEY constraints syntax

Function:PRIMARY KEY constraint uniquely identifies each record in the database table.

Note:The primary key must contain a unique value. Primary key columns cannot contain NULL values. Every table should have a primary key, and every table can only have one primary key.

mysql PRIMARY KEY constraints example

// 在 "Persons" 表创建时在 "Id_P" 列创建 PRIMARY KEY 约束 CREATE TABLE Persons(Id_P int NOT NULL,LastName varchar(255) NOT NULL,FirstName varchar(255),Address varchar(255),City varchar(255),PRIMARY KEY (Id_P));