需求：查詢最近三個月的每一天的業績總和

因為最近三個月每個月的天數是不一樣，所以不能用這篇文章：Mysql查詢最近30天的資料（每天的業績總和資料） 介紹的用固定多少天去查資料。需要一個新方法。

一、生成每個月的每一天的時間序列

SELECT ADDDATE(y.first, x.d - 1) as d
FROM
    (SELECT 1 AS d UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION
 
 ALL
    SELECT 8 UNION ALL SELECT 9 UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL
    SELECT 15 UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL SELECT 18 UNION ALL SELECT 19 UNION ALL SELECT 20 UNION ALL SELECT 21 UNION ALL
    SELECT 22
 
 UNION ALL SELECT 23 UNION ALL SELECT 24 UNION ALL SELECT 25 UNION ALL SELECT 26 UNION ALL SELECT 27 UNION ALL SELECT 28 UNION ALL
    SELECT 29 UNION ALL SELECT 30 UNION ALL SELECT 31) x,
    (SELECT CONCAT('2017-09','-01') as FIRST, DAY(LAST_DAY(str_to_date('2017-09','%Y-%m'))) AS last) y
WHERE x.d <= y.last
 

結果：

二、用上面的時間序列與目標結果集做左連線

SELECT DATE_FORMAT(lefttable.date,'%Y-%c') as yearMonth,lefttable.date,IFNULL(righttable.m,'0') as money
FROM 
        (SELECT ADDDATE(y.first, x.d - 1) as date
FROM
(SELECT 1 AS d UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL
SELECT 8 UNION ALL SELECT 9 UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL
SELECT 15 UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL SELECT 18 UNION ALL SELECT 19 UNION ALL SELECT 20 UNION ALL SELECT 21 UNION ALL
SELECT 22 UNION ALL SELECT 23 UNION ALL SELECT 24 UNION ALL SELECT 25 UNION ALL SELECT 26 UNION ALL SELECT 27 UNION ALL SELECT 28 UNION ALL
SELECT 29 UNION ALL SELECT 30 UNION ALL SELECT 31) x,
(SELECT CONCAT('2017-8','-01') as FIRST, DAY(LAST_DAY(str_to_date('2017-8','%Y-%c'))) AS last) y
WHERE x.d <= y.last and ADDDATE(y.first, x.d - 1)<=CURDATE()) as lefttable
LEFT JOIN 
        (SELECT truncate(sum(af2.money),2) as m,DATE_FORMAT(af2.create_date,'%Y-%c-%d') as gptime 
                from financial_flow af2,vip_student vs1 
                where af2.ACCOUNT_NO IN ('XFSR','XFBK') and DATE_FORMAT(af2.create_date,'%Y-%c')='2017-8' and af2.stu_id=vs1.id and vs1.subject_name='JAVA' GROUP BY gptime)
         as righttable
ON 
DATE_FORMAT(lefttable.date,'%Y-%c-%d')=righttable.gptime

結果：

達到需求目標。