select中使用的所有非聚合函数的列都需要分组，ut.id不是group，在您的情况下，应该从select中删除
尝试

SELECT  Month(FROM_UNIXTIME(ut.created_at)), Count(*) from  $userTable ut 
where FROM_UNIXTIME(ut.created_at) >= CURDATE() - INTERVAL 1 YEAR
GROUP BY Month(FROM_UNIXTIME(ut.created_at));

如果要混合过去12个月的今年和去年的数据，可以使用：

SELECT SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 1) AS Jan,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 2) AS Feb,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 3) AS Mar,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 4) AS Apr,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 5) AS May,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 6) AS Jun,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 7) AS Jul,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 8) AS Aug,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 9) AS Sep,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 10) AS Oct,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 11) AS Nov,
       SUM(MONTH(FROM_UNIXTIME(ut.created_at)) = 12) AS Dec
FROM ut
WHERE FROM_UNIXTIME(ut.created_at) >= CURDATE() - INTERVAL 1 YEAR

注：假设 FROM_UNIXTIME() 实际上是必要的。它还使用一个方便的mysql快捷方式进行条件聚合。

您可以按年份分组，按月份求和，如下所示：

select YEAR(created_at) as year,
  sum(case when Month(created_at) = 1 then 1 else 0 end) AS Jan,
  sum(case when Month(created_at) = 2 then 1 else 0 end) AS Feb,
  sum(case when Month(created_at) = 3 then 1 else 0 end) AS Mar,
  sum(case when Month(created_at) = 4 then 1 else 0 end) AS Apr,
  sum(case when Month(created_at) = 5 then 1 else 0 end) AS May,
  sum(case when Month(created_at) = 6 then 1 else 0 end) AS Jun,
  sum(case when Month(created_at) = 7 then 1 else 0 end) AS Jul,
  sum(case when Month(created_at) = 8 then 1 else 0 end) AS Aug,
  sum(case when Month(created_at) = 9 then 1 else 0 end) AS Sep,
  sum(case when Month(created_at) = 10 then 1 else 0 end) AS Oct,
  sum(case when Month(created_at) = 11 then 1 else 0 end) AS Nov,
  sum(case when Month(created_at) = 12 then 1 else 0 end) AS Dec from ut group by YEAR(created_at)