Replace all tables of a database except one, with data from another db

问题

I have a Django app, the database for which is under active manual development (it's a language-learning app, so it stores vocabulary, grammatical concepts, etc). I'd prefer to do that development in my local django/postgres environment.

However, I don't want to be constantly wiping out the User table from the live version!

I'm very new to Postgres, so please don't assume I know what I'm doing here - would some kind of schema be the right approach here?

回答1:

To just backup the one table, use COPY from inside the database:

COPY user_tbl TO '/path/to/file';

or pg_dump from the shell:

pg_dump -t user_tbl mydb > user_tbl.sql

Then drop the database, restore your new version, empty user_tbl and use COPY FROM to restore the one table:

COPY user_tbl FROM  '/path/to/file';

or restore the backup with the one table from the shell with psql:

psql -f user_tbl.sql mydb

Identify depending tables

Quick and dirty

There is no such thing as "COPY ... CASCADE". The simplest method to identify depending tables would be to start a transaction, call TRUNCATE tbl CASCADE and record the notices you get:

BEGIN;
TRUNCATE user_tbl CASCADE;

NOTICE:  truncate cascades to table "tbl1"
NOTICE:  truncate cascades to table "tbl2"
NOTICE:  truncate cascades to table "tbl3"

Then roll back the transaction - so nothing actually changes:

ROLLBACK;

Careful with that. If you COMMIT the truncate goes through.

Slow and sure

Well, not actually "slow", but the code is a lot more complex. This doesn't take an exclusive lock on the involved tables, though, so it's a lot cleaner and safer:

WITH RECURSIVE x AS (
    SELECT conrelid::regclass
    FROM   pg_constraint
    WHERE  confrelid = 'user_tbl'::regclass

    UNION
    SELECT p.conrelid::regclass
    FROM   x
    JOIN   pg_constraint p ON p.confrelid = x.conrelid
    )
SELECT conrelid::text AS tbl
FROM   x;

Returns:

tbl
------
tbl1
tbl2
tbl3

I use a recursive CTE (requires PostgreSQL 8.4 or later) on the catalog table pg_constraint, because each table can have dependencies in turn.
Use UNION, not UNION ALL to avoid multiple evaluation of tables that might be linked with multiple foreign keys directly or indirectly.

来源：https://stackoverflow.com/questions/13099226/replace-all-tables-of-a-database-except-one-with-data-from-another-db

标签

sql

django

postgresql

database-restore