Mysql多次选择COL以获得不同的值

Question

这是表结构:

ID PID KEY VALUE
1 2 CITY NEW YORK
2 2 COUNTRY UNITED STATES
3 2 STATE NEW YORK
4 1 CITY NEW JERSEY

等等.. 我想要的是获取/过滤结果，如

Where (KEY = CITY and VALUE = NEW YORK) 
      AND (key = country AND VALUE= UNITED STATES)

这将返回空行!

Answer 1

您需要一个 self JOIN。

SELECT t1.*
FROM my_table t1
INNER JOIN my_table t2 ON t1.pid = t2.pid
WHERE t1.key = 'city' and t1.value = 'new york'
  AND t2.key = 'country' and t2.value = 'united states';