postgresql Inheritance Altering tables
Example
Let's create two simple tables:
CREATE TABLE users (username text, email text);
CREATE TABLE simple_users () INHERITS (users);
Adding columns
ALTER TABLE simple_users ADD COLUMN password text;
simple_users
| Column | Type |
|---|---|
| username | text |
| text | |
| password | text |
Adding the same column to the parent table will merge the definition of both columns:
ALTER TABLE users ADD COLUMN password text;
NOTICE: merging definition of column "password" for child "simple_users"
Dropping columns
Using our altered tables:
ALTER TABLE users DROP COLUMN password;
users
| Column | Type |
|---|---|
| username | text |
| text |
simple_users
| Column | Type |
|---|---|
| username | text |
| text | |
| password | text |
Since we first added the column to simple_users, PostgreSQL makes sure this column isn't dropped.
Now if we had another child table, its password column would, of course, have been dropped.
