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 these operations take full locks and may run for long periods.
You can add a new column to a table using the following:
ALTER TABLE mytable ADD COLUMN last_update_timestamp TIMESTAMP WITHOUT TIME ZONE;
Or 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 sequence. This allows you to do a useful trick, which is to add a column unconditionally, using ...