LEFT/RIGHT JOIN不返回空行

我有一個查詢，它使用2個表上的自聯接來返回單行結果。我遇到的問題是，如果seat1是空的，我什麼都沒有返回。LEFT/RIGHT JOIN不返回空行

SELECT seat1.seat_type_id 
    , seat1.seat_type_qty 
    , seat2.seat_type_id 
    , seat2.seat_type_qty 
    FROM jos_sv_apptpro2_requests AS R 
    LEFT JOIN jos_sv_apptpro2_seat_counts AS seat1 ON R.id_requests = seat1.request_id 
    LEFT JOIN jos_sv_apptpro2_seat_counts AS seat2 ON R.id_requests = seat2.request_id 
WHERE (seat1.seat_type_id = 6 AND seat2.seat_type_id = 7) 
    AND R.id_requests = 8703 
    AND R.resource = 3

這應返回：

seat_type_id 6 
seat_type_qty 0 <= this is the empty row 
seat_type_id1 7 
seat_type_qty 1

編輯：現在我已經得到了：

SELECT 
IFNULL(seat1.seat_type_qty,0) AS seat_type_qty, 
IFNULL(seat2.seat_type_qty,0) AS seat_type_qty 
FROM jos_sv_apptpro2_requests AS R 
LEFT JOIN jos_sv_apptpro2_seat_counts AS seat1 
ON R.id_requests = seat1.request_id AND seat1.seat_type_id = 6 
LEFT JOIN jos_sv_apptpro2_seat_counts AS seat2 
ON R.id_requests = seat2.request_id AND seat2.seat_type_id = 7 
WHERE R.id_requests = 8696

重新編輯！ - 我的錯誤是，我在PHP中返回seat_type_qty兩次作爲對象。全部排序 - 謝謝！

來源

2011-12-05 Jeepstone

WHERE seat1.seat_type_id = 6 AND seat2.seat_type_id = 7

是刪除所有具有NULL值的行的內容。你應該將這些條件連接標準，使得RDBMS做你期待什麼：

LEFT JOIN jos_sv_apptpro2_seat_counts AS seat1 ON R.id_requests = seat1.request_id 
               AND seat1.seat_type_id = 6 
LEFT JOIN jos_sv_apptpro2_seat_counts AS seat2 ON R.id_requests = seat2.request_id 
               AND seat2.seat_type_id = 7

來源

2011-12-05 16:15:41 Benoit

你美麗！非常感謝 - 有用的技術知道 – Jeepstone

@Jeepstone：這不是一種真正的技術......它是如何加入工作！當沒有匹配時，OUTER JOIN操作填充具有NULL值的行，並且在所有連接執行完畢後應用WHERE過濾器。 – Benoit

我明白了。不知道現在我上面有什麼錯，但是我得到的結果比預期的要少。 – Jeepstone

移動你的where子句到聯接：

LEFT JOIN jos_sv_apptpro2_seat_counts AS seat1 
    ON (R.id_requests = seat1.request_id) AND (seat1.seat_type_id = 6) 
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

當你有他們在where子句中，你對整行進行匹配。在JOIN中執行它只會對正在加入的特定記錄進行過濾。

來源

2011-12-05 16:16:01

LEFT/RIGHT JOIN不返回空行

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