mysql使用臨時

Question

我的查詢使用一個臨時表，但我做錯了，有人可以告訴我嗎？

EXPLAIN SELECT DISTINCT t.city_id FROM (SELECT city_id FROM `geo__base` Where country = 'DE')as t


id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   SIMPLE  geo__base   ref     country     country     8   const   43460   Using index condition; Using where; Using temporar...

謝謝大家

Answer 1

嘗試這樣的事情：

SELECT DISTINCT city_id FROM (SELECT city_id FROM geo_base WHERE country = 'DE') tmp;

或如上面的fancyPants所述，只需使用以下命令：

 SELECT DISTINCT city_id FROM geo_base;