3

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?

Erwin Brandstetter
  • 185,527
  • 28
  • 463
  • 633
arthur
  • 888
  • 4
  • 13
  • 29

4 Answers4

13

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:

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. 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.

Erwin Brandstetter
  • 185,527
  • 28
  • 463
  • 633
6

Unfortunately it is not easy to parse the RECORD type using PL/pgSQL. If the structure of the tables passed in arguments are always the same as some other table or type you could use this type directly instead of RECORD, and then use the following:

DECLARE
    recCurs table_or_type;
...
BEGIN
...
OPEN recCurs FOR EXECUTE ...
...
EXECUTE 'INSERT INTO ' || events_table_out || ' VALUES(($1).*)'
        USING recCurs;
...

But this will not work with RECORD type. The only solution I can think of is creating the query by hand. But PL/pgSQL gives no way to dynamically get the keys of an RECORD type. So you have to use some external tools. The best (in my opinion) for this kind of job is the hstore extension. Once installed you can create it on your database (the following works only on 9.1+, for earlier you should do it by hand):

CREATE EXTENSION hstore;

Now. You are able to convert a RECORD type to an hstore type, using hstore(recCurs), and so you can dynamically iterate over its keys and values with the each function:

DECLARE
   recCurs record;
   kv record;
   v_cols text;
   v_vals text;
BEGIN
...
    OPEN recCurs FOR EXECUTE ...
...
    -- 1. do something with rec

    -- 2. insert the rec into events_table_out:
    v_cols := '';
    v_vals := '';
    FOR kv IN SELECT * FROM each(hstore(recCurs)) LOOP
        v_cols := v_cols || kv.key || ',';
        v_vals := v_vals || quote_nullable(kv.value) || ',';
    END LOOP;
    v_cols := substr(v_cols, 1, length(v_cols)-1);
    v_vals := substr(v_vals, 1, length(v_vals)-1);
    EXECUTE 'INSERT INTO ' || events_table_out
            || '(' || v_cols || ') '
            || 'VALUES (' || v_vals || ')';
...

Of course, it will only work if the table "pointed" by events_table_out has all the columns that events_table_in has (the first can have more columns).

RESUMING: always you want some dynamic key/value data-type on PL/pgSQL, and RECORD is not enough, the hstore can be used.

MatheusOl
  • 2,549
  • 19
  • 13
0

I needed to do something similar and ended up using the INSERT from SELECT. I need to duplicate records in the same table but changing one field. Maybe it's not the most ellegant solution but it works.

CREATE OR REPLACE FUNCTION public.duplicar_mascotas(
    origen integer DEFAULT 0, 
    destino integer DEFAULT 0
)
 RETURNS integer
 LANGUAGE plpgsql
AS $function$
DECLARE
  fila_mascota record;
  nvo_id_mascota BIGINT;
  contador integer;
  cur_mascotas cursor for
    SELECT id FROM public.mascotas WHERE id_persona = origen;
BEGIN
    contador := 0;
    raise notice 'hola';
    open cur_mascotas;
    loop
        fetch cur_mascotas into fila_mascota;
        exit when not found;
        -- insert del select
        INSERT INTO public.mascotas ( nombre, id_persona, edad_meses) 
        SELECT nombre, destino as id_persona, edad_meses
        FROM public.mascotas
        WHERE 
            id = fila_mascota.id;
        contador := contador + 1;
    end loop;
    return contador;
END;
$function$

Then, i call the function like so:

select duplicar_mascotas (1,2);

This duplicates the records from the person with id = 1 to the person with id = 2.

Mark Torres
  • 1
0

You can use any of the sql commands below:

/* variant 1 */
insert into test_history select v_history_row.*;
/* variant 2 */
execute 'insert into test_history SELECT $1.*' using v_history_row;
LaGen
  • 1
  • 1