Answer
It contains every column the query reads, so the database answers from the index alone and never fetches the table rows (an index-only scan). The cost is a bigger index that every write must also update.
Databases · Flashcard
Databases · Flashcard
It contains every column the query reads, so the database answers from the index alone and never fetches the table rows (an index-only scan). The cost is a bigger index that every write must also update.