Q19
Single choice
Consider the following EXPLAIN of a simple Join:
mysql> EXPLAIN SELECT CountryList.Name, CityList.Name, CityList.Population
-> FROM CountryList JOIN CityList ON CountryList.Code = CityList.Country
-> WHERE CityList.Population > 8000000\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: CountryList
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 239
Extra:
*************************** 2. row ***************************
id: 1
select_type: SIMPLE
table: CityList type:
ALL possible_keys:
NULL key: NULL
key_len: NULL
ref: NULL
rows: 4079
Extra: Using where
How many rows need to be examined to perform the join?