[英]Need help to retrieve data from three MySQL tables
我有三個表,分別是“用戶”,“用戶愛好”和“愛好”。 以下是帶有值的示例表;
以下是用戶表,其中包含fields id, name and age
╔════╦══════╦═════╗
║ ID ║ NAME ║ AGE ║
╠════╬══════╬═════╣
║ 1 ║ abc ║ 23 ║
║ 2 ║ xyz ║ 24 ║
║ 3 ║ pqr ║ 21 ║
╚════╩══════╩═════╝
下面是user_hobbies表,其中包含字段id,user_id和hobby_id
╔════╦═════════╦══════════╗
║ ID ║ USER_ID ║ HOBBY_ID ║
╠════╬═════════╬══════════╣
║ 1 ║ 1 ║ 1 ║
║ 2 ║ 1 ║ 2 ║
║ 3 ║ 1 ║ 3 ║
║ 4 ║ 2 ║ 4 ║
║ 5 ║ 2 ║ 3 ║
║ 6 ║ 2 ║ 5 ║
║ 7 ║ 3 ║ 2 ║
║ 8 ║ 4 ║ 6 ║
╚════╩═════════╩══════════╝
。 以下是帶有字段ID和desc的興趣愛好表
╔════╦═══════════╗
║ ID ║ DESC ║
╠════╬═══════════╣
║ 1 ║ music ║
║ 2 ║ chatting ║
║ 3 ║ cricket ║
║ 4 ║ badminton ║
║ 5 ║ chess ║
║ 6 ║ cooking ║
╚════╩═══════════╝
。 實際要求是我需要一個查詢來檢索姓名,年齡,hobby_id和desc(請參見下面的示例)
╔══════╦═════╦══════════╦═════════════════════════╗
║ NAME ║ AGE ║ HOBBYID ║ DESC ║
╠══════╬═════╬══════════╬═════════════════════════╣
║ abc ║ 23 ║ 1,2,3 ║ music,chatting,cricket ║
║ pqr ║ 21 ║ 2 ║ chatting ║
║ xyz ║ 24 ║ 4,3,5 ║ badminton,cricket,chess ║
╚══════╩═════╩══════════╩═════════════════════════╝
您需要首先連接表,並使用一個稱為GROUP_CONCAT()
的聚合函數。
SELECT a.Name,
a.Age,
GROUP_CONCAT(c.ID) hobbyIDs,
GROUP_CONCAT(c.desc) descList
FROM users a
INNER JOIN user_hobbies b
ON a.ID = b.user_ID
INNER JOIN hobbies c
ON b.hobby_ID = c.ID
GROUP BY a.Name, a.Age
要進一步獲得有關聯接的知識,請訪問以下鏈接:
OUTPUT
╔══════╦═════╦══════════╦═════════════════════════╗
║ NAME ║ AGE ║ HOBBYIDS ║ DESCLIST ║
╠══════╬═════╬══════════╬═════════════════════════╣
║ abc ║ 23 ║ 1,2,3 ║ music,chatting,cricket ║
║ pqr ║ 21 ║ 2 ║ chatting ║
║ xyz ║ 24 ║ 4,3,5 ║ badminton,cricket,chess ║
╚══════╩═════╩══════════╩═════════════════════════╝
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