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boostr.in questions - Question:Primary Keys and Auto Increment Fields


Each table in a database should have a primary key field.

A primary key is used to uniquely identify the rows in a table. Each primary key value must be unique within the table. Furthermore, the primary key field cannot be null because the database engine requires a value to locate the record.

The following example sets the PID field as the primary key field. The primary key field is often an ID number, and is often used with the AUTO_INCREMENT setting. AUTO_INCREMENT automatically increases the value of the field by 1 each time a new record is added. To ensure that the primary key field cannot be null, we must add the NOT NULL setting to the field:

$sql = "CREATE TABLE Persons 
(
PID INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY(PID),
Firstname CHAR(15),
Lastname CHAR(15),
Age INT
)";

 

asked Sep 13, 2013 in PHP by rajesh
edited Sep 12, 2013
0 votes
5 views



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