Using the following query, I'm able to export two tables, selecting 500 items randomly from the first:

copy (select * from (
          select 1 + floor(random() * 1040000)::integer as "documentUUID"
          from generate_series(1, 600) g
          group by 1) r
       join "Document" using ("documentUUID")
      inner join "Citation" on ("Document"."citation_id" = "Citation"."citationUUID")
      limit 500) 
to '/tmp/data.sql';

I want to import this data into my testing database, but COPY FROM doesn't seem to be able to handle multiple table imports.

How can I make this work?

1 Answer 1


Your problem is that the output (row structure) of your query does not match either of your tables.

A possible solution would be creating a temporary table to put in your randomly generated IDs and copying data from one table at a time, using the necessary joins.


SELECT 1 + floor(random() * 1040000)::integer AS documentUUID
  FROM generate_series(1, 500) g;

      SELECT d.*
        FROM Document d
        JOIN doc_ids ON i d.documentUUID = i.documentUUID
  TO /tmp/document_data.sql;

      SELECT c.*
        FROM Citation c
        JOIN Document d ON d.citation_id = c.citationUUID
        JOIN doc_ids ON i d.documentUUID = i.documentUUID
  TO /tmp/citation_data.sql;


Note that I removed the double quotes as they don't make any difference for the given table and column names. Also I don't see what is the merit of grouping when generating the random document IDs. Furthermore, I won't call the IDs ...UUID as UUID is a specific type used very often in very diverse applications.

  • Wow, yeah, this basically worked. The quotes are because I created my tables by migrating from MySQL...and the UUIDs are an old misunderstanding, never to die. Anyway, yes, this works, thanks so much.
    – mlissner
    Commented Sep 16, 2013 at 21:39

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