mysql - 重新映射 MYSQL 中的行

Question

我有这样的表:

uid | fid | value
1   | 1   | nameOf1
1   | 2   | surnameOf1
1   | 3   | countryOf1
2   | 1   | nameOf2
2   | 2   | surnameOf2

并且需要像这样转换/选择它:

uid | name    | surname    | country
1   | nameOf1 | surnameOf1 | countryOf1
2   | nameOf2 | surnameOf2 | ..

Answer 1

尝试如下:

SELECT t1.uid, t2.value AS name, t3.value AS surname, t4.value AS country FROM table t1
  LEFT JOIN table t2 on t2.uid = t1.uid AND t2.fid = 1
  LEFT JOIN table t3 on t3.uid = t1.uid AND t3.fid = 2
  LEFT JOIN table t4 on t4.uid = t1.uid AND t4.fid = 3
  GROUP BY t1.uid;

或者:

SELECT DISTINCT t1.uid, t2.value AS name, t3.value AS surname, t4.value AS country FROM table t1
  LEFT JOIN table t2 on t2.uid = t1.uid AND t2.fid = 1
  LEFT JOIN table t3 on t3.uid = t1.uid AND t3.fid = 2
  LEFT JOIN table t4 on t4.uid = t1.uid AND t4.fid = 3;