左連接多個表格和條件

Question

我想在當前表格被引用到的另一個表格中的值之後進行排序。我的查詢是這樣的：

SELECT o._id, 
     o.titel, 
     o.beschreibung 
FROM `objekt` AS o, 
     `objekt_einzel` AS oe, 
     `objekt_einzel_immobilie` AS oei, 
     `objekt_art` AS oa, 
     `verortung` AS v 
     #here 
     ,`person` AS p, 
     `person_bauträger` AS pb 
     #end 
WHERE o._id = oe.objekt_id 
     AND oe._id = oei.objekt_einzel_id 
     AND oa._id = o.objekt_art_id 
     AND o.ort_id = v._id 
     #here 
     AND oe.bauträger_id = pb._id 
     AND pb.person_id = p._id 
     #end 
     AND (oei.justimmo_objekt_id = "0" 
       OR oei.justimmo_objekt_id IS NULL 
       OR oei.justimmo_objekt_id = "") 
#here 
ORDER BY p.firmenbezeichnung ASC 

查詢工作正常，但它表明我只值如果oe.bauträger_id設置。我也想要null值。所以我需要一個左連接。我嘗試了不同的東西，但我只收到像unknown column這樣的消息，或者我得到的結果太多。

我試圖把它簡化爲這樣：

SELECT o._id, 
     o.titel, 
     o.beschreibung 
FROM `objekt` AS o, 
     `objekt_einzel` AS oe, 
     (SELECT oe.bauträger_id 
     FROM objekt o, objekt_einzel oe, objekt_einzel_immobilie oei 
     WHERE o._id = oe.objekt_id AND oe._id = oei.objekt_einzel_id) AS menge1 
LEFT JOIN 
     (SELECT pb._id AS bauträger_id 
     FROM person p, person_bauträger pb 
     WHERE p._id = pb.person_id) AS menge2 
ON menge1.bauträger_id = menge2.bauträger_id 
WHERE o._id = oe.objekt_id AND oe.bauträger_id = menge1.bauträger_id 

但在這裏我得到一個太大的結果集。我不知道如何更好地解釋這一點。數據集太大而無法創建示例。我希望你明白我的意思。

Answer 1

SELECT o._id, 
     o.titel, 
     o.beschreibung 
FROM `objekt` AS o 
     JOIN `objekt_einzel` AS oe ON o._id = oe.objekt_id 
     JOIN `objekt_einzel_immobilie` AS oei ON oe._id = oei.objekt_einzel_id 
     JOIN `objekt_art` AS oa ON o.objekt_art_id = oa._id 
     JOIN `verortung` AS v ON o.ort_id = v._id 
     LEFT JOIN `person_bauträger` AS pb ON oe.bauträger_id = pb._id 
     LEFT JOIN `person` AS p ON pb.person_id = p._id 
WHERE oei.justimmo_objekt_id = "0" 
     OR oei.justimmo_objekt_id IS NULL 
     OR oei.justimmo_objekt_id = "" 
ORDER BY p.firmenbezeichnung ASC 

這第二次嘗試應該工作，因爲它只是一個使用JOIN語法改寫的原代碼，並與LEFT JOIN的。