mysql - 在单个 SELECT 语句中获取数据的每月分布

Question

我需要使用一个 mysql 语句每月分发我的数据。以下语句的预期结果: 一个包含 12 行的表。如果某一个月没有可用数据，则该月应返回 0。但是，如果数据丢失，则当前 SQL 语句的结果中会丢失一行或多行。我缺少什么？

SELECT m.Month as m1, MONTH(FROM_UNIXTIME(crdate)) as m2,
SUM(CASE WHEN keylock = 1 THEN 1 ELSE 0 END) AS c1, SUM(CASE WHEN keylock = 2 THEN 1 ELSE 0 END) AS c2
FROM tx_bhm_domain_model_access a 
RIGHT OUTER JOIN (
    SELECT 1 AS Month 
    UNION SELECT 2 AS Month 
    UNION SELECT 3 AS Month 
    UNION SELECT 4 AS Month 
    UNION SELECT 5 AS Month 
    UNION SELECT 6 AS Month 
    UNION SELECT 7 AS Month 
    UNION SELECT 8 AS Month 
    UNION SELECT 9 AS Month
    UNION SELECT 10 AS Month 
    UNION SELECT 11 AS Month 
    UNION SELECT 12 AS Month ) m
ON MONTH(FROM_UNIXTIME(a.crdate)) = m.Month
WHERE YEAR(FROM_UNIXTIME(a.crdate))=2018 
GROUP BY m.Month
ORDER BY m.Month

Answer 1

YEAR() 比较需要放在 ON 子句中。我更喜欢LEFT JOIN:

SELECT m.Month as m1, MONTH(FROM_UNIXTIME(crdate)) as m2,
       SUM(CASE WHEN keylock = 1 THEN 1 ELSE 0 END) AS c1,
       SUM(CASE WHEN keylock = 2 THEN 1 ELSE 0 END) AS c2
FROM (SELECT 1 AS Month UNION ALL
      SELECT 2 AS Month UNION ALL 
      SELECT 3 AS Month UNION ALL
      SELECT 4 AS Month UNION ALL 
      SELECT 5 AS Month UNION ALL
      SELECT 6 AS Month UNION ALL
      SELECT 7 AS Month UNION ALL
      SELECT 8 AS Month UNION ALL
      SELECT 9 AS Month UNION ALL
      SELECT 10 AS Month UNION ALL
      SELECT 11 AS Month UNION ALL
      SELECT 12 AS Month
     ) m LEFT JOIN
     tx_bhm_domain_model_access a
     ON MONTH(FROM_UNIXTIME(a.crdate)) = m.Month AND
        YEAR(FROM_UNIXTIME(a.crdate)) = 2018 
GROUP BY m.Month
ORDER BY m.Month;

我还将 UNION 更改为 UNION ALL。无需承担删除重复项的开销。