| Foreign keys with non-matching column definitions [message #65509] |
Mon, 11 October 2004 02:26  |
Tine
Messages: 1
Registered: October 2004
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Junior Member |
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I have read that foreign keys with non-matching column definitions causes poor performance because it forces data conversion.
I wonder if we get a performance degradation when as an example the parent table column definition is set to number(9) and the foreign key column definition is set to number(3)?
Thanks
Tine
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| Re: Foreign keys with non-matching column definitions [message #65511 is a reply to message #65509] |
Mon, 11 October 2004 04:38  |
Art Metzer
Messages: 2480
Registered: December 2002
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Senior Member |
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I wonder if we get a performance degradation when...the parent table column definition is set to number(9) and the foreign key column definition is set to number(3)?
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I doubt it.
Please read the AskTom article "Altering table columns to a smaller size", in which Tom concludes- benchmark these things, get hard and fast numbers before you go about doing long painful changes
- stop doing your conversion [[from NUMBER to NUMBER(12)]]-- it is quite simply "not worth it"
After all, a NUMBER(9) is stored in the database exactly the same as a NUMBER(3) is.
I think the mismatched foreign-key column definitions that you've read about refer to conversions such as between DATE and VARCHAR2, or between NUMBER and VARCHAR2.
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