Select (retrieve) all records from multiple schemas using Postgres

Question

I have a PostgreSQL database with some schemas, like below:

My_Database
 |-> Schemas
    |-> AccountA
    |-> AccountB
    |-> AccountC
    |-> AccountD
    |-> AccountE
           .
           .
           .
    |-> AccountZ

All schemas have a table called product which has a column called title. I would like to know if is possible to execute a select statement to retrieve all records from all schemas with a certain conditional.

The only way I found until now is to run a query account by account, like below.

SET search_path TO AccountA;

SELECT title FROM product WHERE title ILIKE '%test%';

Schemas are created dynamically, so I don't know their names or how many of them exist.

Answer 1

With inheritance like @Denis mentioned, this would be very simple. Works for Postgres 8.4, too. Be sure to consider the limitations.

Basically, you would have a master table, I suppose in a master schema:

CREATE TABLE master.product (title text);

And all other tables in various schemata inherit from it, possibly adding more local columns:

CREATE TABLE a.product (product_id serial PRIMARY KEY, col2 text)
INHERITS (master.product);

CREATE TABLE b.product (product_id serial PRIMARY KEY, col2 text, col3 text)
INHERITS (master.product);

etc.

The tables don't have to share the same name or schema.
Then you can query all tables in a single fell swoop:

SELECT title, tableoid::regclass::text AS source
FROM   master.product
WHERE  title ILIKE '%test%';

tableoid::regclass::text?
That's a handy way to tell the source of each row. Details:

• Find out which schema based on table values

SQL Fiddle.

Answer 2

You basically want a union all:

SELECT title FROM AccountA.product WHERE title ILIKE '%test%'
UNION ALL
SELECT title FROM AccountB.product WHERE title ILIKE '%test%'
UNION ALL
...;

You can do so automatically by using dynamic SQL and the catalog to locate all AccountXYZ schemas that have a products table.

Alternatively, create a AllAccounts schema with similar tables as the ones in individual schemas, and use table inheritance.

Note that neither will tell you which schema the data is from, however. In the former case, this is easy enough to add; not so much in the latter unless you add an extra column.