| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Jakub Ouhrabka <jouh8664(at)ss1000(dot)ms(dot)mff(dot)cuni(dot)cz> |
| Cc: | "Rajesh Kumar Mallah(dot)" <mallah(at)trade-india(dot)com>, pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: why the difference? |
| Date: | 2002-11-21 14:47:20 |
| Message-ID: | 11686.1037890040@sss.pgh.pa.us |
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| Lists: | pgsql-sql |
Jakub Ouhrabka <jouh8664(at)ss1000(dot)ms(dot)mff(dot)cuni(dot)cz> writes:
> the where clause is evaluated before the distinct clause, so your queries
> aren't equivalent because you switched the order by splitting the query
> into two queries...
Besides which, SELECT DISTINCT ON is order-sensitive. If you don't use
an ORDER BY with it, you are going to get rather unpredictable results.
See the example on the SELECT reference page.
regards, tom lane
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