Comments on: Oracle in 3 Minutes: A Ticking Bomb

By: Pythian Group Blog » Blog Archive » Log Buffer #75: a Carnival of the Vanities for DBAs

Fri, 14 Dec 2007 18:00:49 +0000

[...] also has the second episode of his Oracle in 3 Minutes webcast, called A Ticking Bomb, or A Sleeper [...]

By: Eddie Awad

Eddie Awad — Tue, 11 Dec 2007 05:29:50 +0000

@Justin: Good points.

One more thing, if the to_char is used in the WHERE clause, that will break the use of indexes which may impact performance. So, a function based index may be a good option here.

By: Justin Cave

Justin Cave — Tue, 11 Dec 2007 02:59:05 +0000

When trying to filter out rows, be aware that there is no guarantee about what order Oracle executes the various conditions. So you might well find that the invalid number error returns down the road when the query plan changes.

Even if you nest the subquery, i.e.

SELECT t1.col1, t2.col2
  FROM (SELECT t.col1
          FROM table1 t
         WHERE filter_out_non_numbers) t1,
       table2 t2
 WHERE t1.col1 = t2.col1

there is no guarantee that the inner subquery is logically materialized before the join (and the implicit conversion) happens.

By: Patrick Wolf

Patrick Wolf — Mon, 10 Dec 2007 20:25:28 +0000

Yeah, reality sometimes is so far way from the “ideal” world

By: Eddie Awad

Eddie Awad — Mon, 10 Dec 2007 20:21:09 +0000

@Patrick: Sure, if you can change the data model, that will be a very good solution. But, sometimes reality hurts and you’re stuck with a model that you have no control over. I sometimes do find myself in such a situation, unfortunately, especially when I deal with FlexFields (varchar2 columns) in Oracle EBS.

By: Patrick Wolf

Patrick Wolf — Mon, 10 Dec 2007 20:11:42 +0000

Solution 3:

Reconsider your data model if you are really going to compare two columns which obviously have the same content and meaning but are of different data type…

Patrick