Today I Learned

A Hashrocket project

Postgres Intersect

Today I got to see some great SQL debugging that included the use of intersect to compare two datasets.

intersect computes the set intersection of the rows returned by the involved select statements.

Here’s a simple implementation:

dev=# select generate_series(1,1000) intersect 
  select generate_series(10,15);
 generate_series
-----------------
              11
              12
              10
              15
              13
              14

Like a lot of things in Postgres, the order seems deterministic, but not predictable.

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