How to set the primary key in the database

This article mainly introduces the relevant knowledge of "how to set the primary key in the database". The editor shows you the operation process through the actual case, and the operation method is simple, fast and practical. I hope this article "how to set the primary key in the database" can help you solve the problem.

Primary key settin

When we create a table, we usually set a primary key (PRIMARY KEY). We can use the "INT AUTO_INCREMENT PRIMARY KEY" statement to create a primary key, with a starting value of 1, incremented step by step.

If our table has been created, we need to use ALTER TABLE to add the primary key to the table:

Demo_mysql_test.py:

Add a primary key to the sites table.

Import mysql.connector

Mydb = mysql.connector.connect (

Host= "localhost"

User= "root"

Passwd= "123456"

Database= "runoob_db"

)

Mycursor = mydb.cursor ()

Mycursor.execute ("ALTER TABLE sites ADD COLUMN id INT AUTO_INCREMENT PRIMARY KEY")

If you haven't created the sites table yet, you can create it directly using the following code.

Demo_mysql_test.py:

Create a primary key for the table.

Import mysql.connector

Mydb = mysql.connector.connect (

Host= "localhost"

User= "root"

Passwd= "123456"

Database= "runoob_db"

)

Mycursor = mydb.cursor ()

Mycursor.execute ("CREATE TABLE sites (id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR (255), url VARCHAR (255)")

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