3

Note: The solution does not need be optimised for processing speed. It's supposed to be part of a setup phase and won't be run more than once.

General problem

I have X number of tables in a PostgreSQL database with very different names. I can neither be bothered to write the same PostgreSQL commands for each of them, nor can I be sure that the next set of data that I import has the exact same set of tables. Yet I would like to repeat the same action on each of them. How would I go about doing this? Is it even possible?

I will accept an answer that can do this much. However, an answer that does this and also allows me to exclude some tables that I do know the names of would be even better.

Specifics

This question is closely related to another question which details what I want to do with the tables, but both specific and more general answers are appreciated.

Findings

While looking for a solution I found this question, but I don't know if and how I could use those answers. I'm including it here in hopes that someone else might know how to apply them to my question.

3

Thanks to the hint given in the comments by @a_horse_with_no_name I've found the answer in the documentation for the DO command: https://www.postgresql.org/docs/9.6/static/sql-do.html

CREATE TABLE new_table ();
DO $$DECLARE r record;
BEGIN
    FOR r IN SELECT table_name FROM information_schema.tables
         WHERE table_schema = 'public' AND table_type = 'BASE TABLE' AND table_name <> ALL (string_to_array('merge_table,spatial_ref_sys', ','))        LOOP
        -- Stuff that is specific to what I want to do
        EXECUTE 'CREATE TEMP TABLE temp_table AS SELECT * FROM ' || quote_ident(r.table_name) || ' NATURAL FULL OUTER JOIN new_table';
        EXECUTE 'DROP TABLE new_table CASCADE';
        EXECUTE 'CREATE TABLE new_table AS SELECT * FROM temp_table';
        EXECUTE 'DROP TABLE temp_table CASCADE';
        EXECUTE 'DROP TABLE ' || quote_ident(r.table_name) || ' CASCADE';
        -- End of the specific stuff
    END LOOP;
END$$;

Thanks to @a_horse_with_no_name for the suggestion on simplifying the exclusion of specific tables.

EDIT:

I found an even better way to exclude specific tables which at least works for my purposes. What I do is that I run the following query before I import any of the tables that I wish to perform the repeated action on:

DO $$BEGIN
    DROP TABLE IF EXISTS tables;
    CREATE TABLE tables (table_name text);
    INSERT INTO tables (
        SELECT table_name
         FROM information_schema.tables
         WHERE table_schema = 'public'
          AND table_type = 'BASE TABLE'
        );
END$$;

This creates a table containing the names of all the tables (including itself). More tables can of course be added manually with INSERT INTO tables VALUES ('new_table');.
Then in the WHERE clause of the FOR loop, instead of doing table_name <> ALL (string_to_array('merge_table,spatial_ref_sys', ',')) I do table_name NOT IN (SELECT table_name FROM tables). This is much easier to maintain than changing the string whenever new tables to be excluded are introduced.

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