計數患者每月

Question

我想每個月來算耐心，我需要看到結果每個月數哪怕是0

，我運行應該給13上月查詢其他月份的號碼爲3和0。但正在發生的事情是多少13劃分並分配到所有12個月類似如下：

這裏是查詢：

SELECT 
    count(patients) as patients, month 

FROM 
(
    SELECT 
     count(app_id) as patients, 
     month(date_app) as month 
    FROM 
     dentist.appointment 
    WHERE id_logged=1 AND year(date_app)='2016' 
    GROUP BY month(date_app) 

    UNION SELECT 0,1 
    UNION SELECT 0,2 
    UNION SELECT 0,3 
    UNION SELECT 0,4 
    UNION SELECT 0,5 
    UNION SELECT 0,6 
    UNION SELECT 0,7 
    UNION SELECT 0,8 
    UNION SELECT 0,9 
    UNION SELECT 0,10 
    UNION SELECT 0,11 
    UNION SELECT 0,12 
) tmp 
GROUP BY month 

Answer 1

嘗試此查詢：

SELECT 
    count(app_id) as patients, 
    t.m as month 
FROM ( 
    SELECT 1 AS m UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION 
    SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION 
    SELECT 9 UNION SELECT 10 UNION SELECT 11 UNION SELECT 12) AS t 
LEFT JOIN dentist.appointment ON t.m = month(date_app) AND 
      id_logged = 1 AND year(date_app) = 2016 
GROUP BY t.m 

訣竅是首先創建一個包含所有12個月號碼的內聯表格，然後LEFT JOIN將原始表格添加到內嵌表格中。

注：謂詞id_logged = 1和year(date_app) = 2016應放在LEFT JOIN操作的ON子句中，否則LEFT JOIN成爲INNER JOIN。

Demo here