Songjs Songjs - 5 months ago 17
SQL Question

Is HAWQ not support SQL in the cycle(while or for,use plpgsql)?

Today,I defined a function,using the insert statements in a loop. But HAWQ returned an error:

ERROR: could not serialize unrecognized node type: 43983632 (outfast.c:4742)
CONTEXT: SQL statement "insert into t(id,value) values(1,0.1)"
PL/pgSQL function "test_function" line 6 at SQL statement


I did some testing and found that when I use the 'insert statements' in the loop,it will be reported as a mistake.
If I delete the relevant 'insert statements',It can run properly.

Here is an example of a test:



CREATE OR REPLACE FUNCTION test_function()
RETURNS int AS
$BODY$
declare
number int;
begin
number := 1;
while number <= 10 loop
insert into t(id,value) values(1,0.1);
number := number+1;
end loop;
return number;
end
$BODY$
LANGUAGE plpgsql ;





Then I use 'select test_function();' to call the function.It will returned an error mentioned above.

Does this mean that I can not use the SQL statements in a loop with plpgsql ?

Thanks.
Best regards.

Answer

You'll want to avoid singleton statements with HAWQ but I am a little surprised it doesn't work. You'll want to use set based operations instead.

    CREATE TABLE t (id int, value numeric);

    CREATE OR REPLACE FUNCTION test_function() RETURNS int AS
    $BODY$
    declare 
            number int;
    begin       
            insert into t (id, value) select 1, 0.1 from generate_series(1, 10);
            return 10;
    end
    $BODY$
    LANGUAGE plpgsql;

For such a simple example, you could use a sql function instead which has less overhead than plpgsql.

    DROP FUNCTION test_function();

    CREATE OR REPLACE FUNCTION test_function() RETURNS void AS
    $BODY$
            insert into t (id, value) select 1, 0.1 from generate_series(1, 10);
    $BODY$
    LANGUAGE sql;

Both of these functions do all of the work in a single statement rather than executing 10 separate ones. I tested both in HAWQ and both work.

And here is a workaround if you must do singleton insert statements in a loop with HAWQ.

    CREATE OR REPLACE FUNCTION test_function()
      RETURNS int AS
    $BODY$
    declare 
            number int;
            v_sql text;
    begin       
            number := 1;
            while number <= 10 loop
                    v_sql := 'insert into t(id,value) values(1,0.1)';
                    execute v_sql;
                    number := number+1;
            end loop;
            return number;
    end
    $BODY$
      LANGUAGE plpgsql ;