那裏獲取相關表中的所有值均爲空

Question

我正在尋找一種更有效的方式來建立這個查詢記錄（雙子查詢讓我畏縮）：

SELECT contact_id FROM (
    SELECT * FROM (
    SELECT mr.contact_id, di.district 
    FROM recipients mr 
    JOIN address a ON mr.contact_id = a.contact_id 
    JOIN district_values di ON a.id = di.entity_id 
    WHERE mr.mid = 29 
    ORDER BY di.district DESC) addrSingle 
    GROUP BY mr.contact_id) addrNull 
WHERE di.district IS NULL 

讓我解釋一下是怎麼回事。

收件人擁有聯繫人列表。每個聯繫人可能有多個地址。每個地址都有一個相關的district_values表。我需要檢索所有地址的district_values.district列爲空的聯繫人。

例如：

Contact A 
Address 1.district = 4 
Address 2.district = null 
= don't include 

Contact B 
Address 1.district = null 
= include 

Contact C 
Address 1.district = null 
Address 2.district = 3 
= don't include 

我現有查詢的邏輯如下：

1. 檢索與相關地址和地區，爲了讓與非空值的任何地址的聯繫人首先訂購
   
2. 適用於所有組，如果我減少到單個聯繫人記錄，並且如果地區與地區保留
   
3. 適用where子句與至少一個區價值
   

它的工作原理刪除地址 - 它只是有點難看。

Answer 1

你可以試試這個，使用LEFT JOIN並計算相關記錄爲零。

SELECT mr.contact_id 
    FROM recipients mr 
LEFT JOIN address a ON mr.contact_id = a.contact_id 
LEFT JOIN district_values di ON a.id = di.entity_id 
    WHERE mr.mid = 29 
GROUP BY mr.contact_id 
    HAVING COUNT(a.*) = 0 AND COUNT(di.*) = 0