akadia – database design and software engineering

Good publications – for the “hands-on” guys.

A concise description of what is “Selectivity” and “cardinality”

cardinality = nbr of unique/distinct values in a column
selectivity = ratio of (nbr of distinct values/total nbr of records)…

Quiz šŸ™‚
Which columns have the highest selectivity? Ideal selectivity=1
Ans: Primary keys

Bitmap indexes are used for OLAP databases = highly compressed indexes ( on low cardinality columns)
B-Tree indexes are used for OLTP databases = uncompressed. (recommended on high cardinality columns)

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