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samenvatting theorie Relational Databases & Datawarehousing
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samenvatting theorie Relational Databases & Datawarehousing
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1Samenvatting RDDW (theorie)
Hoofstuk 5: indexen...............................................................................................................................3
Hoofdstuk 6: Basics of Transaction Management................................................................................12
Hoofdstuk 7: Datawarehousing + BI (zie ook oefeningen!)..................................................................22
Hoofdstuk 8: NoSQL – Not only SQL.....................................................................................................31
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, 3
Hoofstuk 5: indexen
Intro
Wat?
o Een geordende structuur v/d tabel
o B-tree = balanced tree
Waarom?
o Veel snellere query uitvoering
o Kan unieke rijen forceren
Waarom niet?
o Veel storage (overhead)
o Kan updates, deletes en inserts vertragen, omdat indexen ook veranderd moeten worden
Table Scan
Normaal is de db een heap: data wordt gewoon toegevoegd waar er plaats is
Table scan: een query moet dus heel de tabel overlopen om alle waarden te vinden.
Table Seek
Zoekt naar de index key value ig in de boomstructuur (dus niet heel de tabel moet overlopen
worden, cuz ge navigeert in de boom)
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Clustered index
Is de tabel, waarbij een paar index pagina’s gemaakt zijn zodat queries hier zo kunnen door
navigeren. het wordt een boomstructuur.
o Clustered: direct op de data
o Er kan dus maar 1 clustered index zijn per tabel
Bv telefoonboek: geordend op naam en bovenaan de pagina zieje dan van welke en tot welke
naam er op die pagina staat.
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