Examine this query and output: Which two statements are true? (Choose two.)

Question

Exhibit

Options

• AThe country table is accessed as the first table, and then joined to the city table.
• BIt takes more than 8 milliseconds to sort the rows.
• CThe optimizer estimates that 51 rows in the country table have Continent = `Asia'.
• D35 rows from the city table are included in the result.
• EThe query returns exactly 125 rows.

• A
  5% (2)
• B
  10% (4)
• C
  65% (26)
• E
  20% (8)

Explanation

Options C and D correctly describe what can be read from a MySQL EXPLAIN output. The rows column in EXPLAIN shows the optimizer's estimate of rows to be examined per table - so seeing 51 for the country table filtered on Continent = 'Asia' is exactly that: an estimate (C). Likewise, the 35 shown for the city table represents the rows the optimizer expects to process from that table in the join (D).

Why the distractors fail:

• A is wrong because EXPLAIN output lists tables in access order, and if city appears first, it's accessed first - not country. The join direction is the opposite of what A claims.
• B is wrong because EXPLAIN (without ANALYZE) shows cost/row estimates, not actual execution time - there are no millisecond timings in standard EXPLAIN output.
• E is wrong because the rows column is an estimate, not a guarantee. The actual number of returned rows can differ from what the optimizer predicts.

Memory tip: Think "EXPLAIN = estimates, not facts." The rows column is always the optimizer's guess - never the exact result count. Table order in the output = the join access order, so read top-to-bottom to trace which table gets hit first.

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