mysql：将两列合并为两行

Question

我有以下声明

SELECT disease.id, disease.name, disease_synonym.name FROM disease JOIN disease_synonym where diseaseId=code

结果是一个带有 id 和两列名称的表。 我如何将其转换为只有 id 和名称的 2 列？ （当然，id现在会出现几次）

再见，

尼科

Answer 1

想到了两种方法...

运行查询两次（一次用于名称，一次用于同义词），然后将结果合并在一起......

SELECT disease.id, disease.name FROM disease

UNION ALL

SELECT disease.id, disease_synonym.name FROM disease JOIN disease_synonym where diseaseId=code

或加入两行表，并使用 CASE 语句执行 pivot...

SELECT
  disease.id,
  CASE WHEN pivot.field = 'name' THEN disease.name
       WHEN pivot.field = 'syno' THEN disease_synonym.name
  END
FROM
  disease
INNER JOIN
  disease_synonym
    ON diseaseId=code
CROSS JOIN
  (SELECT 'name' AS field UNION ALL SELECT 'syno' AS field) AS Pivot

Answer 2

我想你想要SELECT disease.id, disease_synonym.name FROM...不是吗？ 只显示同义词名称？