On 11/19/2014 08:26 AM, Anil Menon wrote:
Hello, I would like to ask from your experience which would be the best "generic" method for checking if row sets of a certain condition exists in a PLPGSQL function. I know of 4 methods so far (please feel free to add if I missed out any others) 1) get a count (my previous experience with ORCL shaped this option) select count(*) into vcnt from table where <<condition>> if vcnt >0 then do X else do y end if Cons : It seems doing a count(*) is not the best option for PG
Well that would depend on the table size, whether it was 100 rows vs 1,000,000 rows
2) Use a non-count option select primary_key_Col into vcnt from table where <<condition>> if found then do X else do y end if Cons :Some people seems not to prefer this as (AFAIU) it causes a plpgsql->sql->plpgsql switches
plpgsql is fairly tightly coupled to SQL, so I have not really seen any problems. But then I am not working on large datasets.
3) using perform perform primary_key_Col into vcnt from table where <<condition>> if found then do X else do y end if Seems to remove the above (item 2) issues (if any)
AFAIK, you cannot do the above as written. PERFORM does not return a result: http://www.postgresql.org/docs/9.3/interactive/plpgsql-statements.html#PLPGSQL-STATEMENTS-SQL-NORESULT It would have to be more like: perform primary_key_Col from table where <<condition>>
4) using exists if exists ( select 1 from table where <<condition>> ) then do x else do y end if My question is what would be the best (in terms of performance) method to use? My gut feeling is to use option 4 for PG. Am I right or is there any other method?
All of the above is context specific. To know for sure you will need to test on actual data.
Thanks in advance Anil
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