Code has been added to clipboard!

SQL ALTER TABLE

Reading time 2 min
Published Aug 9, 2017
Updated Nov 20, 2019

TL;DR – The ALTER TABLE statement in SQL is used to delete, add, or modify table columns. You can also use it to drop and add various table constraints.

Adding a new column to the table

Example
ALTER TABLE mytable_name
ADD mycolumn_name datatype;

Note: the new column will be added to the end of the table by default. You can add multiple columns by separating them with commas.

Deleting a column

Example
ALTER TABLE mytable_name
DROP COLUMN mycolumn_name;

Changing the data type of a particular column

Note: when changing the data type, make sure the old one and the new one are compatible. Otherwise, you might get conversion errors.

In MySQL / Oracle (< 10G)

Example
ALTER TABLE mytable_name
MODIFY COLUMN mycolumn_name datatype;

In SQL Server / MS Access

Example
ALTER TABLE mytable_name
ALTER COLUMN mycolumn_name datatype;
Udacity
Pros
  • Simplistic design (no unnecessary information)
  • High-quality courses (even the free ones)
  • Variety of features
Main Features
  • Nanodegree programs
  • Suitable for enterprises
  • Paid certificates of completion
Coursera
Pros
  • Professional service
  • Flexible timetables
  • A variety of features to choose from
Main Features
  • Professional certificates of completion
  • University-level courses
  • Multiple Online degree programs
Datacamp
Pros
  • Great user experience
  • Offers quality content
  • Very transparent with their pricing
Main Features
  • Free certificates of completion
  • Focused on data science skills
  • Flexible learning timetable

In Oracle 10G and later

Example
ALTER TABLE mytable_name
MODIFY mycolumn_name datatype;

Examples using a demo database

The Developers table

ID Name City Country
1 Tom Kurkutis New York USA
2 Ana Fernandez London UK
3 Antonio Indigo Paris France
4 Aarav Kaelin Delhi India
5 Andrew Tumota Miami USA
6 Basma Zlata Miami USA

Adding a column called BirthDate

Example
ALTER TABLE Developers
ADD BirthDate date;

The result

ID Name City Country BirthDate
1 Tom Kurkutis New York USA
2 Ana Fernandez London UK
3 Antonio Indigo Paris France
4 Aarav Kaelin Delhi India
5 Andrew Tumota Miami USA
6 Basma Zlata Miami USA

Changing the data type to year

Example
ALTER TABLE Developers
ALTER COLUMN BirthDate year;

Deleting the BirthDate column

Example
ALTER TABLE Developers
DROP COLUMN BirthDate;

The result

ID Name City Country
1 Tom Kurkutis New York USA
2 Ana Fernandez London UK
3 Antonio Indigo Paris France
4 Aarav Kaelin Delhi India
5 Andrew Tumota Miami USA
6 Basma Zlata Miami USA

Latest Udacity Coupon Found:

Verified STAFF PICK

75% OFF COURSES

Udacity Black Friday Offer

The best time to save on Udacity courses is now - follow this coupon to access a 75% Udacity Black Friday discount & enjoy learning at a very low cost!

Expiration date: 03/03/2021
3176 People Used
Only 97 Left
Rating
5.0