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Message Posted: Wed, 16 Nov 2011 @ 11:13:04 GMT
| Subj: | | Re: NOT ( columnname is NULL) condition in a LOJ |
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| From: | | Victor Sokovin |
Anomy.Anom wrote:
| | In an explain involving a LOJ , it reads something like this ... | |
| | NOT ( col1 ?is NULL) and then it mentions about doing the LOJ. I can understand the NOT NULL approach but its doing this even AFTER that
column is already defined as NOT NULL in the DDL. Why have this NOT NULL check on a column that is guaranteed to be a NOT NULL 'by birth' | |
When you deal with outer joins NULLs can appear in the result set of the query even for columns that are 'by birth' NULL-free. So far nothing
surprising in the explain.
There is still a group of data modelers out there who spend their time eliminating poor NULLs from their models and databases because they read
somewhere that NULLs are not so good. It is a rather useless approach if outer joins are going to be used.
Victor
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