Insert values from a record variable into a table

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?

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
  LANGUAGE plpgsql 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
$func$;

Call (important!):

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

t and t1 being tables with identical schema.

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:

• Insert values from a record variable into a subclass table

Major ingredients

-
Implicit cursor of a FOR loop instead of explicit cursor. That's generally preferable.

-
Polymorphic types

-
Object identifier types

-
Dynamic SQL in plpgsql

-
VALUES can take a row type directly.

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. Just use NULL.

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

db<>fiddle here

Old sqlfiddle

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.

StackExchange Database Administrators Q#52826, answer score: 13