SQL PRIMARY KEY
SQL PRIMARY KEY Constraint
The PRIMARY KEY constraint uniquely identifies each record
in a database table.
Primary keys must contain UNIQUE values, and cannot contain
NULL values.
A table can have only one primary key, which may consist of
single or multiple fields.
SQL PRIMARY KEY on CREATE TABLE
The following SQL creates a PRIMARY KEY on the
"ID" column when the "Persons" table is created:
MySQL:
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (ID)
);
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (ID)
);
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