knowledge/The WITH statement.md

tags
database, potsgresql, transaction, sql, english

The WITH statement

Allows to save into variables tables results returned from a SELECT or INSERT ... RETURNING statement, and use them in following querys.

Also allows to chain multiple INSERTS, and if any of them fails, all previous INSERTS are rolledback.
Note: autoincrements still increase on failures, hence skipped.

So It's excellent to avoid explicitly using transactions

Example

WITH inserted_user as (
    INSERT INTO users (username, name, password_hash)
    VALUES ('master', 'master', '$argon2i$v=19$m=4096,t=10,p=1$l9mKHF/++OJO4Fzj5VvOxw$smezKrrynx74W2+7L4zyiKUXWFdQDqdKf2RBMU4p0JI')
    RETURNING user_id
), inserted_role as (
    INSERT INTO roles (name)
    VALUES ('master')
    RETURNING role_id
), t as (
    INSERT INTO join_users_roles (user_id, role_id)
    SELECT user_id, role_id
    FROM inserted_user, inserted_role
)
INSERT INTO join_roles_permissions (role_id, permission_id)
SELECT role_id, permission_id FROM inserted_role, permissions;

What led to learning this

• Needed to insert a bunch of data atomically accross many tables, see the example above. Working on a tiny family project