Question

基本上，当某个值（在我的例子中为COMMUNICATIONS_ID）相等时，我试图总结计算字段的值。这些分数与相同的COMMUNICATIONS_ID相关联，我想总结这些值。

我是SQL新手，这是我误导的第一次尝试：

SELECT *
FROM consumer_action_log as cal1
JOIN consumer_action_log as cal2
    ON cal1.COMMUNICATIONS_ID=cal2.COMMUNICATIONS_ID
    AND cal1.COMM_TYPE_ID=4

Answer 1

SELECT COMMUNICATIONS_ID, SUM(fieldName) 
FROM consumer_action_log
WHERE COMM_TYPE_ID = 4
GROUP BY COMMUNICATIONS_ID

我认为没有必要在这里加入表格。

Answer 2

分割ON和WHERE条件可能更好，即使INNER JOIN的结果相同也是如此。使两个表的链接更加清晰。

SELECT sum(cal2.somecolumn)
FROM consumer_action_log as cal1
JOIN consumer_action_log as cal2
    ON cal1.COMMUNICATIONS_ID=cal2.COMMUNICATIONS_ID
WHERE cal1.COMM_TYPE_ID=4

在COMM_TYPE_ID=4
加入cal2（自连接），其中COMMUNICATIONS_ID等于cal1
总结来自cal2的一些列

如果COMMS_TYPE_ID=4上的过滤器导致多个cal1.COMMUNICATIONS_ID，那么您需要GROUP BY COMMUNICATIONS_ID（与cal1或cal2无关 - 它们是相同的）

SELECT cal2.COMMUNICATIONS_ID, sum(cal2.somecolumn)
FROM consumer_action_log as cal1
JOIN consumer_action_log as cal2
    ON cal1.COMMUNICATIONS_ID=cal2.COMMUNICATIONS_ID
WHERE cal1.COMM_TYPE_ID=4
GROUP BY cal2.COMMUNICATIONS_ID

总结MySQL计算字段，其中列值相同

2 个答案: