November 2006
Intermediate to advanced
168 pages
3h 17m
German
Content preview from MySQL: kurz & gut
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1.8. Funktionen
MySQL stellt eingebaute Funktionen zur Verfügung, die besondere Operationen ausführen.
1.8.1. Aggregatfunktionen
Aggregatfunktionen operieren auf Datenmengen. Sie werden üblicherweise verwendet, um eine Aktion auf einer vollständigen Menge von zurückgegebenen Zeilen auszuführen. Beispielsweise würde SELECT AVG(hoehe) FROM kinder den Durchschnitt aller Werte im hoehe-Feld der kinder-Tabelle zurückgeben.
AVG( Ausdruck)
Gibt den Durchschnitt der Werte in Ausdruck zurück (z.B. SELECT AVG(note) FROM test).
BIT_AND( Ausdruck)
Gibt die bitweise UND-Verknüpfung aller Werte in Ausdruck zurück (z.B. SELECT BIT_AND(flags) FROM option). Ein Bit wird im Ergebnis gesetzt, wenn dieses Bit in allen Eingabewerten gesetzt ist.
BIT_OR( Ausdruck ...
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