Mysql SQL-选择两年

我对以下sql代码有问题： 我想打印出这两个年份（2019年和2020年）的计数。 现在我只打印2020。你有什么想法或者可以帮我解决这个问题吗

     SELECT COUNT(u.id) AS total,  m.displayMonth
         FROM (
               SELECT 'Jan' as displayMonth, '01' AS MONTH
               UNION SELECT 'Feb' as displayMonth, '02' AS MONTH
               UNION SELECT 'Mar' as displayMonth,'03' AS MONTH
               UNION SELECT 'Apr' as displayMonth,'04' AS MONTH
               UNION SELECT 'May' as displayMonth,'05' AS MONTH
               UNION SELECT 'Jun' as displayMonth,'06' AS MONTH
               UNION SELECT 'Jul' as displayMonth,'07' AS MONTH
               UNION SELECT 'Aug' as displayMonth,'08' AS MONTH
               UNION SELECT 'Sep' as displayMonth,'09' AS MONTH
               UNION SELECT 'Okt' as displayMonth,'10' AS MONTH
               UNION SELECT 'Nov' as displayMonth,'11' AS MONTH
               UNION SELECT 'Dec' as displayMonth,'12' AS MONTH
              ) AS m
    LEFT JOIN wpiy_veosoft_crm_customer u 
    ON MONTH(STR_TO_DATE(CONCAT(m.month, ' 2020'),'%m %Y')) = MONTH(u.date)
       AND YEAR(u.date) = '2020'
    GROUP BY m.month

下面的SQL代码将打印出以下内容：

total   DisplayMonth
7           Jan
0           Feb
0           Mar
0           Apr
0           May
0           Jun
0           Jul
0           Aug
0           Sep
0           Okt
0           Nov
0           Dec

我想为2020年和2019年打印。下面的打印图是这样的：

2019   2020    DisplayMonth
 5      7           Jan
 2      0           Feb
 1      0           Mar
 0      0           Apr
 0      0           May
 0      0           Jun
 0      0           Jul
 2      0           Aug
 1      0           Sep
 0      0           Okt
 4      0           Nov
 1      0           Dec

---

您可以使用条件聚合：

 SELECT m.displayMonth,
        SUM(CASE WHEN YEAR(u.date) = 2019 THEN 1 ELSE 0 END ) as total_2019,
        SUM(CASE WHEN YEAR(u.date) = 2020 THEN 1 ELSE 0 END ) as total_2020
 FROM (SELECT 'Jan' as displayMonth, '01' AS MONTH UNION ALL
       SELECT 'Feb' as displayMonth, '02' AS MONTH UNION ALL
       SELECT 'Mar' as displayMonth, '03' AS MONTH UNION ALL
       SELECT 'Apr' as displayMonth, '04' AS MONTH UNION ALL
       SELECT 'May' as displayMonth, '05' AS MONTH UNION ALL
       SELECT 'Jun' as displayMonth, '06' AS MONTH UNION ALL
       SELECT 'Jul' as displayMonth, '07' AS MONTH UNION ALL
       SELECT 'Aug' as displayMonth, '08' AS MONTH UNION ALL
       SELECT 'Sep' as displayMonth, '09' AS MONTH UNION ALL
       SELECT 'Okt' as displayMonth, '10' AS MONTH UNION ALL
       SELECT 'Nov' as displayMonth, '11' AS MONTH UNION ALL
       SELECT 'Dec' as displayMonth, '12' AS MONTH
      ) m LEFT JOIN
      wpiy_veosoft_crm_customer u 
      ON MONTH(u.date) = m.month AND  -- implicit conversion here
         YEAR(u.date) IN (2019, 2020)
GROUP BY m.month, m.displayMonth
ORDER BY m.month;

请注意对查询的更改：

• 使用

  UNION ALL

  代替

  UNION

  。没有理由产生删除重复项的开销
• 日期比较只是使用日期部分

---

请尝试将以下代码放入聚合函数中，并根据条件进行更改

SELECT COUNT(u.id) AS total,  m.displayMonth,year(u.date)
         FROM (
               SELECT 'Jan' as displayMonth, '01' AS MONTH
               UNION SELECT 'Feb' as displayMonth, '02' AS MONTH
               UNION SELECT 'Mar' as displayMonth,'03' AS MONTH
               UNION SELECT 'Apr' as displayMonth,'04' AS MONTH
               UNION SELECT 'May' as displayMonth,'05' AS MONTH
               UNION SELECT 'Jun' as displayMonth,'06' AS MONTH
               UNION SELECT 'Jul' as displayMonth,'07' AS MONTH
               UNION SELECT 'Aug' as displayMonth,'08' AS MONTH
               UNION SELECT 'Sep' as displayMonth,'09' AS MONTH
               UNION SELECT 'Okt' as displayMonth,'10' AS MONTH
               UNION SELECT 'Nov' as displayMonth,'11' AS MONTH
               UNION SELECT 'Dec' as displayMonth,'12' AS MONTH
              ) AS m
    LEFT JOIN wpiy_veosoft_crm_customer u 
    ON  MONTH(u.date) = m.month

       AND YEAR(u.date) in(‘2019’, '2020')
    GROUP BY m.month,year(u.date)

---

嗨，戈登。很好，问题是当我运行代码时，如果count=0，它会显示NULL。一月二月二日三月二日零1@Victor . . . 我用

CASE

表达式替换了simper布尔逻辑，从而消除了这个问题。