CODEWITHSUNDEEP
sql-serversql-server-2005
Roshan
Roshan

Reputation: 717

Deleting columns in MS SQL Server

How do I delete a column from an existing table?

Upvotes: 51

Views: 77802

Answers (5)

Saravanan B
Saravanan B

Reputation: 21

ALTER TABLE [Intake].[MER_SF_Opportunity_History] DROP COLUMN [[IntakeIsDeleted]]]
GO

Upvotes: 1

Tony L.
Tony L.

Reputation: 19406

This can also be done through the SSMS GUI.

I like this method because it warns you if there are any relationships on that column and can also automatically delete those as well. As PaxDiablo states, if there are relationships, they must be deleted first.

  1. Put table in Design view (right click on table) like so:

enter image description here

  1. Right click on column in table's Design view and click "Delete Column"

enter image description here

At this point, if there are any relationships that would also need to be deleted, it will ask you if you would like to delete those as well.

Upvotes: 5

Joakim Backman
Joakim Backman

Reputation: 1907

ALTER TABLE XXX DROP COLUMN YYY;

Upvotes: 14

paxdiablo
paxdiablo

Reputation: 881613

The command you're looking for is:

alter table tblName drop column columnName

where tblName is the name of the table and columnName is the name of the column, but there's a few things you may need to do first.

  • If there are any foreign key references to the column, you'll need to get rid of them first.
  • If there's an index using that column, you'll need to either get rid of it or adjust it to not use that column.

Keep in mind that the performance of this command may not necessarily be good. One option is to wait for a down-time period when you can be certain no-one will be accessing the database, rename the current table, then use create table and insert into ... select from to transfer the columns you don't want deleted.

One of the later releases of Oracle actually has a soft delete which can just marks a column as unused without removing it physically. It has the same effect since you can no longer reference it and there's a command along the lines of alter table ... drop unused columns which is meant to be run in quiet time, which does the hard work of actually removing it physically.

This has the advantage of "disappearing" the columns immediately without dragging down database performance during busy times.

Upvotes: 105

Unsliced
Unsliced

Reputation: 10552

For large tables this can be very slow. It can often be a lot faster to create a new table, a duplicate of the old one but with the changes, and insert the data. Drop the old table and then rename the new table.

Upvotes: 3

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