MySQL的：條件帶走筆記

Question

我有一個請求，該計數所有未去除的紙幣和未去除的音符與特定值：

SELECT 
    catalogs.id AS id, 
    COUNT(DISTINCT t.id) AS total, 
    COUNT(DISTINCT c.id) AS closed 
FROM catalogs 
LEFT JOIN links t ON catalogs.id = t.catalog 
LEFT JOIN links c ON catalogs.id = c.catalog 
WHERE catalogs.removed = 0 
    AND (t.removed = 0 OR t.removed is NULL) 
    AND (c.removed = 0 OR c.removed is NULL) 
    AND (c.is_open = 0 OR c.is_open is NULL) 
GROUP BY catalogs.id 
ORDER BY catalogs.id; 

但在性反應的我只能看到註釋，其中總= 0或其中存在至少一個注意到c.is_open = 0

UPD 0：我不是非常接近與SQL，但我意識到我的方式試圖解決的問題......不要臉我:(

upd 1：我有另外一個（先回答）方式，使此查詢與SUM（），語法是

SUM(case when links.removed = 1 then 1 else 0 end) AS removed 

對我來說這是一個比較容易。

Answer 1

嘗試從WHERE子句中移動對其他列的檢查，以ON條款： -

SELECT 
    catalogs.id AS id, 
    COUNT(DISTINCT t.id) AS total, 
    COUNT(DISTINCT c.id) AS closed 
FROM catalogs 
LEFT JOIN links t ON catalogs.id = t.catalog AND t.removed = 0 
LEFT JOIN links c ON catalogs.id = c.catalog AND c.removed = 0 AND (c.is_open = 0 OR c.is_open is NULL) 
WHERE catalogs.removed = 0 
GROUP BY catalogs.id 
ORDER BY catalogs.id;