即使特定月份不存在數據，如何在 MySQL 中檢索按月記錄？

SELECT COUNT(`userID`) AS total, DATE_FORMAT(`userRegistredDate`, '%b') AS MONTH, YEAR(`userRegistredDate`) AS year
FROM `users`
GROUP BY DATE_FORMAT(FROM_UNIXTIME(`userRegistredDate`, '%b'))

SELECT COUNT(u.userID) AS total, m.month
FROM (
SELECT 'Jan' AS MONTH
UNION SELECT 'Feb' AS MONTH
UNION SELECT 'Mar' AS MONTH
UNION SELECT 'Apr' AS MONTH
UNION SELECT 'May' AS MONTH
UNION SELECT 'Jun' AS MONTH
UNION SELECT 'Jul' AS MONTH
UNION SELECT 'Aug' AS MONTH
UNION SELECT 'Sep' AS MONTH
UNION SELECT 'Oct' AS MONTH
UNION SELECT 'Nov' AS MONTH
UNION SELECT 'Dec' AS MONTH
) AS m
LEFT JOIN users u
ON MONTH(STR_TO_DATE(CONCAT(m.month, ' 2013'),'%M %Y')) = MONTH(u.userRegistredDate)
AND YEAR(u.userRegistredDate) = '2013'
GROUP BY m.month
ORDER BY 1+1;

SELECT COUNT(u.userID) AS total, DATE_FORMAT(merge_date,'%b') AS month, YEAR(m.merge_date) AS year
FROM (
SELECT '2013-01-01' AS merge_date
UNION SELECT '2013-02-01' AS merge_date
UNION SELECT '2013-03-01' AS merge_date
UNION SELECT '2013-04-01' AS merge_date
UNION SELECT '2013-05-01' AS merge_date
UNION SELECT '2013-06-01' AS merge_date
UNION SELECT '2013-07-01' AS merge_date
UNION SELECT '2013-08-01' AS merge_date
UNION SELECT '2013-09-01' AS merge_date
UNION SELECT '2013-10-01' AS merge_date
UNION SELECT '2013-11-01' AS merge_date
UNION SELECT '2013-12-01' AS merge_date
) AS m
LEFT JOIN users u
ON MONTH(m.merge_date) = MONTH(u.userRegistredDate)
AND YEAR(m.merge_date) = YEAR(u.userRegistredDate)
GROUP BY m.merge_date
ORDER BY 1+1;