Deferring Index costs for table to table copies in PostgreSQL
When bulk copying data to a table, it is much faster if the destination table is index and constraint free, because it is cheaper to build an index once than maintain it over many inserts. For...
View ArticleMultiple Phrase Search in PostgreSQL
Tsearch, the full text search engine in PostgreSql, is great at rapidly searching for keywords (and combinations of keywords) in large bodies of text. It does not, however, excel at matching multi-word...
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Redundant Indexing in PostgreSQL
If you have a table with a column included as the first column in a multi-column index and then again with it’s own index, you may be over indexing. Postgres will use the multi-column index for queries...
View ArticleComputing Distinct Items Across Sliding Windows in SQL
As a member of PatientsLikeMe‘s Data team, from time to time we’re asked to compute how many unique users did action X on the site within a date range, say 28 days, or several date ranges (1,14,28 days...
View ArticleAnother use for generate_series: row multiplier
I had a request the other day: how many simultaneous users are on the site, by time of day. I already have a session database that’s computed nightly from weblogs: it contains the times at which each...
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