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Re: [PROGRAMMERING] [SQL] group by hjælp



Jesper Krogh wrote:
Hvilket absolut er en bug i mysql..

Der findes ingen record i den oprindelige tabel der har id 1 og pris
180. Mysql returnerer data der ikke eksisterer.

Det er en dokumenteret bug/feature i MySQL, at den tillader select af felter, der ikke er med i GROUP BY (og heller ikke er funktionelt afhængig af GROUP-felterne).


Ligeledes er det dokumenteret, at hvis man benytter sig af dette, kan man ikke forudsige, hvilken af rækkerne i en gruppe, de enkelte felter skal komme fra.

Citat fra http://dev.mysql.com/doc/refman/5.1/en/group-by-hidden-fields.html

Do not use this feature if the columns you omit from the GROUP BY part are not constant in the group. The server is free to return any value from the group, so the results are indeterminate unless all values are the same.

Med venlig hilsen

Ole

 
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