DatabasesIntermediate
Composite Index
PronunciationKOM-po-zit IN-deks
Definition
A composite index is a database index created on two or more columns of a table. It allows the database to efficiently search for rows based on combinations of those columns.
Where you hear it
Database performance tuning sessions, schema design reviews, and when optimizing slow SQL queries.
Examples
We added a composite index on
(last_name, first_name)to speed up our user search feature.The query is slow because it filters by
categoryandcreated_atwithout a matching composite index.
Common mistake
Assuming that a composite index on (A, B) automatically speeds up queries that only filter by column B alone; it usually only works if the query includes the leftmost column A.