Mysql

MySQL Altering tables

The format of an existing database table can be changed with an ALTER TABLE query . This query can make a single alteration or specify as number of alterations as comma-separated list.

In the ADD COLUMN and DROP COLUMN examples the COLUMN  keyword is optional- it is what the manual calls “a pure noise word” that is only there to aid readability.


An ALTER TABLE query can ADD a complete new COLUMN to an existing table , like this :

ALTER TABLE table-name;
ADD COLUMN column-name data-type optional-modifier/s;

It can also ADD a PRIMARY KEY to an existing column definition using this syntax :

ALTER TABLE table-name;
ADD PRIMARY KEY (column-name);

An ALTER TABLE query can CHANGE the name of an existing column. The new column will not inherit any data type or modifiers specified to the original column – these must be set a new in the ALTER TABLE query, like this :

ALTER TABLE table-name;
CHANGE old-column-name new-column-name data-type optional-modifiers/s;

delete an entire column from the table using the DROP COLUMN keywords :

ALTER TABLE table-name;
DROP COLUMN column-name;

Ex :

ALTER TABLE Emp_Data
ADD PRIMARY KEY (id),
ADD COLUMN code INT UNIQUE NOT NULL,
CHANGE Emp_Name VARCHAR(100)
NOT NULL,
DROP COLUMN Emp_Address;

Recommended Tutorials for you


Related posts

MySQL Command-line

Anuj Kumar

MySQL SELECT DISTINCT

Anuj Kumar

MySQL PHP Connections

Anuj Kumar

MySQL Introduction

Anuj Kumar

MySQL Select Query

Anuj Kumar

MySQL Users

Anuj Kumar

MySQL Column Modifiers

Anuj Kumar

MySQL Database and Tables

Anuj Kumar

How to use mysql through cmd

Anuj Kumar

Leave a Comment

* By using this form you agree with the storage and handling of your data by this website.

This site uses Akismet to reduce spam. Learn how your comment data is processed.