Re: no_data_found oracle vs pg

Thanks Pavel,

 

I know I can test the ROWCOUNT or the FOUND indicator, but it’s not what I want.

I want a NO_DATA_FOUND exception to be raised when the function is called from a PL/pgSQL block, and I want the function to return a NULL value when called from SQL.

 

Regards

 

From: Pavel Stehule <pavel.stehule@gmail.com>
Sent: Saturday, September 16, 2023 4:06 PM
To: Jean-Marc Voillequin (MA) <Jean-Marc.Voillequin@moodys.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: no_data_found oracle vs pg

 

Hi so 16. 9. 2023 v 13: 27 odesílatel Jean-Marc Voillequin (MA) <Jean-Marc. Voillequin@ moodys. com> napsal: Hello everyone, On Oracle, a no_data_found exception is raised from pl/sql but not from sql (it returns null). It's well known. 

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Hi

 

so 16. 9. 2023 v 13:27 odesílatel Jean-Marc Voillequin (MA) <Jean-Marc.Voillequin@moodys.com> napsal:

Hello everyone,

On Oracle, a no_data_found exception is raised from pl/sql but not from sql (it returns null). It's well known.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> create or replace function hello return char is
  2  c char;
  3  begin
  4     select 'a' into c from dual where 1=2;
  5     return c;
  6  end;
  7  /

Function created.

SQL> select coalesce(hello(),'<NULL>') from dual;

COALESCE(HELLO(),'<NULL>')
--------------------------------------------------------------------------------
<NULL>

SQL> declare
  2  res char;
  3  begin
  4     res:=hello();
  5  end;
  6  /

declare
*
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at "JM.HELLO", line 4
ORA-06512: at line 4


On PG, with the strict keyword, we get:

psql (15.2)
Type "help" for help.

JM=> create or replace function hello_strict() returns char language plpgsql as $function$
JM$> declare
JM$> c char;
JM$> begin
JM$>   select 'a' into strict c where 1=2;
JM$>   return c;
JM$> end;$function$;
CREATE FUNCTION

JM=> select coalesce(hello_strict(),'<NULL>');

ERROR:  query returned no rows
CONTEXT:  PL/pgSQL function hello_strict() line 5 at SQL statement

JM=> do $$declare
JM$> res char;
JM$> begin
JM$>   res:=hello_strict();
JM$> end$$;

ERROR:  query returned no rows
CONTEXT:  PL/pgSQL function hello_strict() line 5 at SQL statement
PL/pgSQL function inline_code_block line 4 at assignment


And without the strict keyword:

JM=> create or replace function hello_not_strict() returns char language plpgsql as $function$
JM$> declare
JM$> c char;
JM$> begin
JM$>   select 'a' into c where 1=2;
JM$>   return c;
JM$> end;$function$;
CREATE FUNCTION

JM=> select coalesce(hello_not_strict(),'<NULL>');
 coalesce
----------
 <NULL>
(1 row)

JM=> do $$declare
JM$> res char;
JM$> begin
JM$>   res:=hello_not_strict();
JM$> end$$;
DO
JM=>

I have tons of functions to migrate from Oracle to PG. They are both called from SQL or PL/SQL.
I would like to avoid to create two functions (_strict and _not_strict).

A kind of proxy function that is lazy to evaluate its argument would be helpful:
select do_not_raise_no_data_found(hello_strict());

 

The STRICT keyword can be replaced by test of number of returned rows

 

so you can do some like

 

DECLARE rows int; target record;

BEGIN

  SELECT * FROM foo INTO target;

  GET DIAGNOSTICS rows = ROW_COUNT;

  IF rows <> 1 THEN

    /* do what you want */

  END IF;

END;

 

Regards

 

Pavel

 

 

Or maybe a parameter to set just prior to exec sql.
set do_not_raise_no_data_found_in_sql=true;
select hello_strict();

Or something else.
Any good idea is welcome!

I've been able to transpose to PG all Oracle specific features ((+) left join operator, connect by, packages, etc).
It was a big challenge almost successful.
But I cannot figure out how to solve this strict/not strict difference in a smart way. This is my last blocking point. It makes me crazy!

Thanks & Regards

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