MySQL的SELECT語句應該返回一個唯一的行

Question

我有以下幾列名，排名，CREATED_DATE在表1。

我想

SELECT 
    name, 
    rank for latest created_date, 
    latest created_date, 
    difference between rank current created_date & previous date 
FROM 
    table1 

有每人CREATED_DATE人只有一個記錄。

輸出應該是：

Sam 15 2011/10/05 -3 

感謝您的幫助。

Answer 1

SELECT 
    name, 
    rank, 
    created_date, 
    rank - (
    SELECT rank FROM table1 AS bar 
    WHERE bar.created_date < foo.created_date 
    ORDER BY created_date DESC 
    LIMIT 1 
) AS diff 
FROM table1 AS foo 
ORDER BY created_date DESC 
LIMIT 1 

編輯：重讀你的問題，我想你想獲得一個輸出行每人，隨着最後兩個記錄的那個人之間計算得到的差值。如果是這樣，則需要一個稍微複雜的解決方案：

SELECT 
    name, 
    rank, 
    created_date, 
    rank - (
    SELECT rank FROM table1 AS bar 
    WHERE bar.name = foo.name AND bar.created_date < foo.created_date 
    ORDER BY created_date DESC LIMIT 1 
) AS diff 
FROM table1 AS foo 
NATURAL JOIN (
    SELECT name, MAX(created_date) AS created_date FROM table1 
    GROUP BY name 
) AS blah