Strange issue when running sql with false condition

Question

Hi,
I'm running this query from the application:
select 22
from DUAL
where ( to_number(0) <> 0 ) and exists (
select 'X'
from TABULA.macdent$FNCITEMS
where ( macdent$FNCITEMS.QIV = to_number(0) ) );
And it takes a long time because it is checking the second condition.
Even though the first one is False.
When running it through sqlplus it takes nothing. and of course no rows returns.
The 0 in to_number is a bind variable
it looks like this:
select :intvar
from DUAL
where ( to_number(:QIV$) <> 0 ) and exists ( select 'X'
from TABULA.macdent$FNCITEMS
where ( macdent$FNCITEMS.QIV = to_number(:QIV$) ) )
1 - filter predicate: ( IS NOT NULL AND 0<>TO_NUMBER(TO_CHAR(:QIV$)))
But in sqlplus the filter predicates is different.
1 - filter(NULL IS NOT NULL AND EXISTS (SELECT 0 FROM "TABULA"."MACDENT$FNCITEMS" "MACDENT$FNCITEMS" WHERE
SQL> select 22
from DUAL
where ( to_number(0) <> 0 ) and exists (
select 'X'
from TABULA.macdent$FNCITEMS
where ( macdent$FNCITEMS.QIV = to_number(0) ) );
2 3 4 5 6
no rows selected
Elapsed: 00:00:00.00
Execution Plan
Plan hash value: 883410849
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
Time | TQ |IN-OUT| PQ Distrib |
| 0 | SELECT STATEMENT | | 1 | | 0 (0)| | | | |
|* 1 | FILTER | | | | | | | | |
| 2 | FAST DUAL | | 1 | | 2 (0)|00:00:01 | | | |
| 3 | PX COORDINATOR | | | | | | | | |
| 4 | PX SEND QC (RANDOM)| :TQ10000 | 63M| 782M| 2 (0)|00:00:01 | Q1,00 | P->S | QC (RAND) |
| 5 | PX BLOCK ITERATOR | | 63M| 782M| 2 (0)|00:00:01 | Q1,00 | PCWC | |
|* 6 | TABLE ACCESS FULL| MACDENT$FNCITEMS | 63M| 782M| 2 (0)|00:00:01 | Q1,00 | PCWP | |
Predicate Information (identified by operation id):
1 - filter(NULL IS NOT NULL AND EXISTS (SELECT 0 FROM "TABULA"."MACDENT$FNCITEMS" "MACDENT$FNCITEMS" WHERE
"MACDENT$FNCITEMS"."QIV"=0))
6 - filter("MACDENT$FNCITEMS"."QIV"=0)
ANY SUGGESTIONS?
Thanks,

Answer 1

912294 wrote:
Hi,
I'm running this query from the application:
select 22
from DUAL
where ( to_number(0) <> 0 ) and exists (
select 'X'
from TABULA.macdent$FNCITEMS
where ( macdent$FNCITEMS.QIV = to_number(0) ) );
Why are you using "to_number(0)"? the zero is already seen by oracle as a number.
The to_number function expects to get a character string as the argument: to_number('0')
See the difference?
As you currently have it coded, you are forcing oracle to do an implicit conversion of the number zero to the character string '0' in order to pass it to to_number to convert it back to the number zero.
And what is the point of "where to_number(0) <> 0"
When would that EVER be true?
And it takes a long time because it is checking the second condition.
Even though the first one is False.
When running it through sqlplus it takes nothing. and of course no rows returns.
The 0 in to_number is a bind variable
it looks like this:
select :intvar
from DUAL
where ( to_number(:QIV$) <> 0 ) and exists ( select 'X'
from TABULA.macdent$FNCITEMS
where ( macdent$FNCITEMS.QIV = to_number(:QIV$) ) )
So the query you showed at the top is not the query we are really dealing with. What is the data type of QIV$? At least now we know that comparison to zero is not a fixed value.
1 - filter predicate: ( IS NOT NULL AND 0<>TO_NUMBER(TO_CHAR(:QIV$)))
This suggests QIV$ is already a number, else why would you pass it to to_char? And as I said above, if it is already a number, why pass it to to_number? Here you appear to be explicitly doing what I described oracle as implicitly doing in your first query above.
But in sqlplus the filter predicates is different.
1 - filter(NULL IS NOT NULL AND EXISTS (SELECT 0 FROM "TABULA"."MACDENT$FNCITEMS" "MACDENT$FNCITEMS" WHERE
SQL> select 22
from DUAL
where ( to_number(0) <> 0 ) and exists (
select 'X'
from TABULA.macdent$FNCITEMS
where ( macdent$FNCITEMS.QIV = to_number(0) ) );
2 3 4 5 6
no rows selected
Elapsed: 00:00:00.00
Execution Plan
Plan hash value: 883410849
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
Time | TQ |IN-OUT| PQ Distrib |
| 0 | SELECT STATEMENT | | 1 | | 0 (0)| | | | |
|* 1 | FILTER | | | | | | | | |
| 2 | FAST DUAL | | 1 | | 2 (0)|00:00:01 | | | |
| 3 | PX COORDINATOR | | | | | | | | |
| 4 | PX SEND QC (RANDOM)| :TQ10000 | 63M| 782M| 2 (0)|00:00:01 | Q1,00 | P->S | QC (RAND) |
| 5 | PX BLOCK ITERATOR | | 63M| 782M| 2 (0)|00:00:01 | Q1,00 | PCWC | |
|* 6 | TABLE ACCESS FULL| MACDENT$FNCITEMS | 63M| 782M| 2 (0)|00:00:01 | Q1,00 | PCWP | |
Predicate Information (identified by operation id):
1 - filter(NULL IS NOT NULL AND EXISTS (SELECT 0 FROM "TABULA"."MACDENT$FNCITEMS" "MACDENT$FNCITEMS" WHERE
"MACDENT$FNCITEMS"."QIV"=0))
6 - filter("MACDENT$FNCITEMS"."QIV"=0)
ANY SUGGESTIONS?
Thanks,