根據MySQL中另一個表的數據構建是/否列

Question

所以我有一堆表，每個表都有關於用戶的某種數據。

table 1: first_name, last_name, email
table 2: info_1, info_2, info_3

我正在嘗試構建一個SELECT查詢，該查詢將用於構建一個VIEW，看起來像這樣

SELECT first_name, last_name, email, has_info_1, has_info_2, has_info_3 FROM tables1, 2 WHERE some condition.

但是，我並不想實際獲取info_1,2,3數據，而只是想檢查表2中是否存在該數據，並在has_info_1,2,3中說Y或N。

我希望這是有道理的。

Answer 1

像這樣：

SELECT
  Table1.First_Name,
  Table1.Last_Name,
  Table1.Email,
  CASE WHEN Table2.Info_1 IS NULL THEN 'No' ELSE 'Yes' END AS Has_Info_1,
  CASE WHEN Table2.Info_2 IS NULL THEN 'No' ELSE 'Yes' END AS Has_Info_2,
  CASE WHEN Table2.Info_3 IS NULL THEN 'No' ELSE 'Yes' END AS Has_Info_3
FROM Table1
LEFT JOIN Table2 ON Table1.Whatever = Table2.Whatever