总结MySQL计算的字段，其中列值相同

Question

基本上，当某个值（在我的案例Communications_ID中）相等时，我试图总结计算字段的值。这些分数与相同的Communication_ID相关联，我想总结这些值。

我是SQL的新手，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

我认为不需要在这里加入桌子。

Answer 2

即使内在连接的结果相同，也最好将ON和条件分开。更清楚地链接了两个表。

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

• 查找cal1记录 COMM_TYPE_ID=4
• 加入CAL2（自加入），communications_id等于cal1
• 总结一下Cal2的一些列

如果过滤器 COMMS_TYPE_ID=4 导致多个 cal1.COMMUNICATIONS_IDS，那么您将要 GROUP BY communications_id（从Cal1或Cal2中无关紧要 - 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