Category Archives: SQL

Perfect hash function for weekday names

This is probably only of limited usefulness in practice, but it came as a spinoff from a discussion on #postgresql. The basic problem is, given a string which you already know is an English weekday name, return the day number … Continue reading

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Performance issues with ORed conditions

An issue that comes up from time to time on the IRC channel is performance optimization of queries that contain ORed conditions. Here is a summary of the common problems and some solutions.

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Range aggregation with window functions

This article is also available on the PG wiki here This problem is one I’ve been asked about a couple of times on IRC; the solution involves some tricks with window functions that have a fairly wide range of applications. … Continue reading

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On Normalization

People have funny ideas about database normalization. What normalization is not: creating an (id,value) table for every single piece of data is not normalization using surrogate keys for everything is not normalization a way to improve performance (though it sometimes … Continue reading

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