Change primary key in PostgreSQL table

Question

I have users table in my PostgreSQL 9.3.6 database with two columns: id and another_id. The id is a primary key,

Answer 1

I've spent some time and finally came up with a working solution.

I will publish it here for future reference.

Solution

First of all, you have three tables (foo_table, bar_table, baz_table) which are pointing to your users table by means of foreign keys (called user_id in all cases). You will need to replace the IDs stored in those columns from id to another_id. Here's how you can do it:

-- We are dropping the foreign key constraint on dependant table (in other case it will prevent us from updating the values)
ALTER TABLE foo_table DROP CONSTRAINT fk_e52ffdeea76ed395;

-- Then, we're swapping values in foreign key column from id to another_id
UPDATE foo_table T SET user_id = (SELECT another_id FROM users WHERE id = T.user_id);

-- And finally we're creating new foreign key constraint pointing to the another_id instead of id
ALTER TABLE foo_table ADD CONSTRAINT fk_e52ffdeea76ed395 FOREIGN KEY (user_id) REFERENCES users (another_id) ON DELETE CASCADE;

You will need to repeat the above queries for each dependent table.

After that, all dependent tables will point to your new another_id column.

In the end we will just need to replace the primary key:

-- 1. Dropping the original primary key
ALTER TABLE users DROP CONSTRAINT users_pkey

-- 2. Renaming existing index for another_id (optional)
ALTER INDEX uniq_1483a5e93414710b RENAME TO users_pkey

-- 3. Creating new primary key using existing index for another_id
ALTER TABLE users ADD PRIMARY KEY USING INDEX users_pkey

-- 4. Creating index for old id column (optional)
CREATE UNIQUE INDEX users_id ON users (id)

-- 5. You can drop the original sequence generator if you won't need it
DROP SEQUENCE users_id_seq

You can even drop the original id column if you want to.

I hope it will help someone.