A query needs 5 rows out of a million. Which access method fits?

• An index scan to those rows
• A full scan of the table
• A full scan, then a sort of all rows

What is a query plan?

• The query's SQL text, tidied and reformatted
• A log of how long each past query took
• Its chosen methods, order and row estimates

Most rows of the table qualify for the query. Which method usually wins?

• Reading the server log
• A full scan
• An index on another table

Two tiny tables join. Which method do you expect?

• Hash join, because it always wins on joins
• Sort merge, because tiny inputs are already sorted
• Nested loop, because its setup stays tiny

One plan step estimates 50 rows but processes 400,000. What do you conclude?

• That step likely picked the wrong method
• The query uses no joins at all
• The row counts are close enough to ignore here

The step that does the most work of its own is always the one that runs last.

Switching a big join from nested loop to hash can help once inputs grow.

A slow plan shows a nested loop over a step estimated at 20 rows with 200,000 real rows. What would you change?

• Fix the wrong estimate or add the missing index
• Add two more joins to the query
• Delete the table statistics