Migrating Uber from MySQL to PostgreSQL

Code Changes
Implicit Ordering (cont.)
SELECT * FROM trips WHERE status =
’completed’;
Without an index on status, the query scans the rows in
PK order, so the same implicit ordering on id will occur.
With an index on status, the query scans the row in
order of (status, id), and thus there is still an
implicit ordering on id! (This would not be true for a
“range” query, however.)
Evan Klitzke (Uber, Inc.) Migrating Uber from MySQL to PostgreSQL March 13, 2013 42 / 59