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Hoorcollege 4, Samenvatting gegevensbeheer
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Hoorcollege 4, Samenvatting gegevensbeheer. Eerstejaars forensisch onderzoek saxion
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📂Week 4 Gegevensbeheer
Hoorcollege 4 Databases || SQL data querying
Donker groene tekst is wat je letterlijk intypt in SQLite en wat je hiervoor als resultaat terug krijgt staat
in het licht groen.
SELECT || selecteer kolommen
*betekend selecteer alle kolommen van genres
Week 4 Gegevensbeheer 1
, Er wordt hier van de tabel customers de city geselecteerd waarbij alleen de customers worden laten
zien die in het land united kingdom wonen :
Door het woord DISTINCT toe te voegen krijg je geen duplicaten in je tabel (geen dubbele steden) :
Functies
De x in (x) staat voor de naam van een attribuut
avg(x) || gemiddelde van alle waardes van attribuut x
count(x) || aantal waardes van attribuut x
count(DISTINCT x) || aantal verschillende waardes van attribuut x
max(x) || grootste waarde van attribuut x
Week 4 Gegevensbeheer 2
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