Question

这是表格结构：

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)

那是空行！

Answer 1

你需要一个自我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';

Answer 2

因此，您在同一列中拥有一个包含不同类型值的表，其中一个字段标识每个集合（PID）。这是对的吗？

如果是这样，那么你需要在这里进行自我加入：

SELECT
    DISTINCT cityTable.PID
FROM
    tableName AS cityTable
JOIN
    tableName AS countryTable
    ON cityTable.PID = countryTable.PID
WHERE
    cityTable.key = "city"
    AND
    cityTable.value = "NEW YORK"
    AND
    countryTable.key = "country"
    AND
    countryTable.value = "UNITED STATES";

Mysql为不同的值多次选择COL

2 个答案: