Getting weird issue with TO_NUMBER function in Oracle

Question

I have been getting an intermittent issue when executing to_number function in the where clause on a varchar2 column if number of records exceed a certain number n. I used n as there is no exact number of records on which it happens. On one DB it happens after n was 1 million on another when it was 0.1. million.

E.g. I have a table with 10 million records say Table Country which has field1 varchar2 containing numberic data and Id

If I do a query as an example

select * 
from country 
where to_number(field1) = 23
and id >1 and id < 100000

This works

But if I do the query

select * 
from country 
where to_number(field1) = 23 
and id >1 and id < 100001

It fails saying invalid number

Next I try the query

select * 
from country
where to_number(field1) = 23 
and id >2 and id < 100001

It works again

As I only got invalid number it was confusing, but in the log file it said

Memory Notification: Library Cache Object loaded into SGA
Heap size 3823K exceeds notification threshold (2048K)
KGL object name :with sqlplan as (
    select c006 object_owner, c007 object_type,c008 object_name
      from htmldb_collections
     where COLLECTION_NAME='HTMLDB_QUERY_PLAN'
       and c007 in ('TABLE','INDEX','MATERIALIZED VIEW','INDEX (UNIQUE)')),
ws_schemas as(
    select schema 
      from wwv_flow_company_schemas
     where security_group_id = :flow_security_group_id),
t as(
        select s.object_owner table_owner,s.object_name table_name,
               d.OBJECT_ID
          from sqlplan s,sys.dba_objects d

It seems its related to SGA size, but google did not give me much help on this.

Does anyone have any idea about this issue with TO_NUMBER or oracle functions for large data?

Answer 1

Assuming you know that the given range of ids will always result in field1 containing numeric data, you could do this instead:

select *
from (
  select /*+NO_MERGE*/ * 
  from country 
  where id >1 and id < 100000
)
where to_number(field1) = 23;