Summary: in this tutorial, you’ll learn how to drop one or more columns in a table by using the Db2 ALTER TABLE DROP COLUMN statement.
Introduction to Db2 ALTER TABLE DROP COLUMN statement
Sometimes, you may want to delete one or more unused columns from a table. To do this, you use the ALTER TABLE DROP COLUMN statement as follows:
1 2 | ALTER TABLE table_name DROP COLUMN column_name; |
In this syntax:
- First, specify the name of the table from which you want to drop the column in the
ALTER TABLEclause. - Second, specify the name of the column that you want to delete in the
DROP COLUMNclause.
To delete multiple columns, you can use the following syntax:
1 2 3 4 | ALTER TABLE table_name DROP COLUMN column_name_1 DROP COLUMN column_name_2 ...; |
Note that there is no comma between the DROP COLUMN clauses.
Db2 ALTER TABLE DROP COLUMN examples
We’ll use the orders table created in the ALTER TABLE tutorial for the demonstration.
1) Dropping one column example
The following example removes the note column from the orders table:
1 2 | ALTER TABLE orders DROP COLUMN note; |
To verify the change, you can use the DESCRIBE TABLE command:
1 | DESCRIBE TABLE orders; |
Here is the output:
The note column has been dropped.
2) Dropping multiple columns example
This example uses the ALTER TABLE DROP COLUMN to drop the requested_date and order_status columns:
1 2 3 | ALTER TABLE orders DROP COLUMN requested_date DROP COLUMN order_status; |
The following picture shows the column list of the orders table after executing the above statement:
1 | DESCRIBE TABLE orders; |
In this tutorial, you’ve learned how to drop one or more unused columns from a table by using the Db2 ALTER TABLE DROP COLUMN statement.