Thread: pgsql-general@postgresql.org

Hi,

I am trying to use cursors and I am really frustrated already. Do  I
need to install an extension?

1. Problem number one is that what ever I use in front of the fetch
command it is not being accepted, it gives a syntax error. If I use a
number ,"all" or "forward" it gives an error again?????????? I want to
do something like the code below:

CREATE OR REPLACE FUNCTION database_correction()
  RETURNS double precision AS
$BODY$
DECLARE
    mycursor CURSOR FOR select distinct(fund_id) from
"NAV_values_bfb_history";
    iterator integer;

BEGIN
open mycursor;

FETCH mycursor INTO iterator;

--fetch next  from  mycursor  --gives  an error

WHILE (FETCH next from mycursor) LOOP
    -- some computations here
END LOOP;

CLOSE mycursor;
END;

2. What is the right way to check that the cursor has ended. In
sqlserver there is a variable "@@fetch_status". I have to make here some
comparison in the while clause, but I am not sure what it should be. I
could not find a single example for cursor in a loop.

I will greatly appreciate any help, pgsql is my database of choice.

Cheers,
Anton

Anton Andreev wrote:
> Hi,
>
> I am trying to use cursors and I am really frustrated already. Do  I
> need to install an extension?

No, you just need to have a look at the docs.
http://www.postgresql.org/docs/8.2/static/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING

> 1. Problem number one is that what ever I use in front of the fetch
> command it is not being accepted, it gives a syntax error. If I use a
> number ,"all" or "forward" it gives an error again?????????? I want to
> do something like the code below:
>
> CREATE OR REPLACE FUNCTION database_correction()
>  RETURNS double precision AS
> $BODY$
> [...]

Try something like this:

CREATE OR REPLACE FUNCTION database_correction()
 RETURNS double precision LANGUAGE plpgsql AS
$body$
DECLARE
   fund INTEGER;
BEGIN
   FOR fund IN SELECT DISTINCT(fund_id) FROM "NAV_values_bfb_history" LOOP
     RAISE NOTICE $$ foo bar $$;
     -- some computations here
   END LOOP;
   RETURN 42.0;
END;
$body$;

--
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

> I am trying to use cursors and I am really frustrated already. Do  I
> need to install an extension?

No, it's all in the documentation:
http://www.postgresql.org/docs/current/static/plpgsql-control-structures
.html#PLPGSQL-RECORDS-ITERATING

> 1. Problem number one is that what ever I use in front of the fetch
> command it is not being accepted, it gives a syntax error. If I use a
> number ,"all" or "forward" it gives an error again?????????? I want to
> do something like the code below:
>
> CREATE OR REPLACE FUNCTION database_correction()
>   RETURNS double precision AS
> $BODY$
> DECLARE
>     mycursor CURSOR FOR select distinct(fund_id) from
> "NAV_values_bfb_history";
>     iterator integer;
>
> BEGIN
> open mycursor;
>
> FETCH mycursor INTO iterator;
>
> --fetch next  from  mycursor  --gives  an error
>
> WHILE (FETCH next from mycursor) LOOP
>     -- some computations here
> END LOOP;
>
> CLOSE mycursor;
> END;

My suggestion:

$BODY$
DECLARE
    a_row RECORD;
BEGIN
   FOR a_row IN SELECT DISTINCT(fund_id) FROM "NAV_values_bfb_history"
LOOP
      -- some computations here
      -- access the value as "a_row.fund_id"
   END LOOP;
END;
$BODY$

> 2. What is the right way to check that the cursor has ended. In
> sqlserver there is a variable "@@fetch_status". I have to make here
some
> comparison in the while clause, but I am not sure what it should be. I
> could not find a single example for cursor in a loop.

You do not need that at all, the loop will be left if there are no more
results.

Yours,
Laurenz Albe