Adding/removing columns on a table

As designs change, we may want to add or remove columns from our data tables. These are common operations in development, though they need more careful planning on a running production database server as they take full locks and may run for long periods.

How to do it…

You can add a new column to a table using the following command:

ALTER TABLE mytable
ADD COLUMN last_update_timestamp TIMESTAMP WITHOUT TIME ZONE;

You can drop the same column using the following command:

ALTER TABLE mytable
DROP COLUMN last_update_timestamp;

You can combine multiple operations when using ALTER TABLE, which then applies the changes in a sequence. This allows you to perform a useful trick, which is to add a column unconditionally using IF EXISTS, which is useful because ADD COLUMN does not allow IF NOT EXISTS:

ALTER TABLE mytable
DROP COLUMN IF EXISTS last_update_timestamp,ADD COLUMN last_update_timestamp TIMESTAMP...