Free Indexes, queries and scale lessonsIndexes, queries and scale · Stage 1 · Indexes · Step 2
Composite, covering and selective indexes
Pick an index for a real query: the order of columns, whether it can cover the query, and whether it will be used at all. About 14 minutes.
You have an index on (last_name, first_name). Which query can NOT use it to seek?
- AWHERE first_name = 'Priya'
- BWHERE last_name = 'Rao'
- CWHERE last_name = 'Rao' AND first_name = 'Priya'
Show the answer
WHERE first_name = 'Priya'. It skips the leading column: the first names are scattered through the index.
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