Postgresql – Insert values from a record variable into a table

functionsinsertplpgsqlpostgresqlrecord

I am developing a user-defined function that takes two arguments:

create or replace function gesio(
    events_table_in regclass,  
    events_table_out regclass)
returns void as $$ ... $$

events_table_in and events_table_out have exactly the same schema.

Simply explained, I loop through the records of events_table_in, manipulate the records and want to append (insert) the manipulated records into events_table_out in the following fashion:

OPEN recCurs FOR execute 
format('SELECT * FROM %s order by session_id, event_time', event_table_in);

LOOP
    FETCH recCurs into rec;
    if not found then
      exit;
    end if;

    -- 1. do something with rec

    -- 2. insert the rec into events_table_out

end loop;

How can I save the rec into events_table_out?

Best Answer

There is a solution with just PL/pgSQL. Simple and elegant, too. Pretty advanced stuff, though.
Requires Postgres 9.0 or later (workaround for older versions possible).

CREATE OR REPLACE FUNCTION gesio(_tbl_in anyelement, _tbl_out regclass)
  RETURNS void AS
$func$
BEGIN

FOR _tbl_in IN EXECUTE
   format('SELECT * FROM %s', pg_typeof(_tbl_in))
LOOP
   -- do something with record

   EXECUTE format('INSERT INTO %s SELECT $1.*', _tbl_out)
   USING _tbl_in;
END LOOP;

END
$func$  LANGUAGE plpgsql;

Call (important!):

SELECT gesio(NULL::t, 't1');

t and t1 being the tables with identical schema.

Note that the polymorphic parameter (anyelement) is only needed if you need it's value or data type for the computation in the function body. Else you can simplify like demonstrated in this later answer:

Major ingredients

An obstacle to overcome is that variables inside the function cannot be defined as polymorphic type anyelement (yet). This related answer on SO explains the solution. Provides a workaround for older versions, too.

I am handing in a NULL value of type t, which serves three purposes:

  • Provide table name.
  • Provide table type.
  • Serve as loop variable.

The value of the first parameter is discarded. Use NULL.

Consider this related answer on SO with more details. The most interesting part being the last chapter Various complete table types.

SQL Fiddle demo.

If your computations are not too sophisticated, you may be able to replace the loop with a single dynamic SQL statement, which is typically faster.

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