Question

我有一个名为“ menergy”的表，其中包含下一个结构和数据示例：

--------------------------------------------------------------
time | m_value | pt_periode | meter_id_meter | mtype_id_type |
--------------------------------------------------------------
t1   | 10      |  0         |      1         |      24       |
t1   |  5      |  0         |      1         |      25       |
t1   | 15      |  0         |      1         |      26       |
t1   | 20      |  0         |      1         |      27       |
t1   | 500     |  0         |      1         |      0002     |

mtype有4种类型，因此在mType = 24、25、26、27而不是0002的情况下，条件：same time, same pt_periode, same meter_id将其m_value求和。例如，条件可能是：

  (meter_id_meter = 1 and mtype_id_type = 24 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 25 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 26 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 27 and pt_periode = 0)

因此，在最后一个数据示例中，我想要的结果是：10 + 5 + 15 + 20 = 50。所以我想得到50 我已经阅读了有关IF条件和JOIN的信息，但是它需要创建另一个表。但是，我尝试了下一个，但是语法错误：

SELECT
  timestampadd(month, -1, time_stamp) as "time",
  if ((meter_id_meter = 1 and mtype_id_type = 24 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 25 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 26 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 27 and pt_periode = 0), SUM(m_value)) as "Q"
FROM menergy

Answer 1

我怀疑您应该使用where子句。

SELECT   SUM(m_value)) as "Q"
FROM menergy
where meter_id_meter = 1 and pr_periode = 0 and mtype_id_type in (2,25,26,27)

但是我不知道您要如何将timestampadd（month，-1，time_stamp）设置为“时间”，

Answer 2

查看您的代码似乎需要将if条件为true的值求和，因此请尝试使用where

SELECT  timestampadd(month, -1, time_stamp) as "time", SUM(m_value)) as "Q"

FROM menergy
WHERE  (
  (meter_id_meter = 1 and mtype_id_type = 24 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 25 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 26 and pt_periode = 0) or
  (meter_id_meter = 1 and mtype_id_type = 27 and pt_periode = 0) 
)
group by  timestampadd(month, -1, time_stamp)

或简单地

WHERE meter_id  = 1  AND pt_periode = 0 and mtype in (24,25,26,27)

有没有一种方法可以将同一列依赖于另一列求和？

2 个答案: