Question

我在Postgres数据库中有此表和数据样本

CREATE TABLE testAAA(Id integer PRIMARY KEY, datum date, COLA text, COLB text, COLC text, COLD int);

/* Create few records in this table */
INSERT INTO testAAA VALUES(1,to_date('01/01/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPA','1');
INSERT INTO testAAA VALUES(2,to_date('01/02/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPA','1');
INSERT INTO testAAA VALUES(3,to_date('01/03/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPA','1');
INSERT INTO testAAA VALUES(4,null,'PLANTA','VENDORA','OPA','1');
INSERT INTO testAAA VALUES(5,to_date('01/10/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPA','5');
INSERT INTO testAAA VALUES(6,to_date('01/10/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPA','10');
INSERT INTO testAAA VALUES(7,to_date('01/11/2018','dd/mm/yyyy'),'PLANTA','VENDORB','OPA','50');
INSERT INTO testAAA VALUES(8,to_date('01/10/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPA','10');
INSERT INTO testAAA VALUES(9,to_date('01/11/2018','dd/mm/yyyy'),'PLANTA','VENDORA','OPB','5');
COMMIT;

我正在尝试根据条件和组合得出平均值：

SELECT COLA,COLB,COLC,
CASE
  WHEN (datum >= now() - interval '6 month') THEN SUM(COLD)/6
  ELSE '0'
END AS datum_range
FROM testAAA
group by COLA,COLB,COLC;

我的目标是使用COLA + COLB + COLC组合生成COLD列最近6个月的平均值，如果满足DATE间隔条件，则跳过空值。

现在我遇到此错误：

Error(s), warning(s):

42803: column "testaaa.datum" must appear in the GROUP BY clause or be used in an aggregate function

如何解决以上错误？

Answer 1

demo:db<>fiddle

SELECT *,
    SUM(COLD) FILTER (WHERE datum >= now() - interval '6 month') OVER (PARTITION BY COLA, COLB, COLC) / 6.0 as avg
FROM testAAA

结果：

| id |      datum |   cola |    colb | colc | cold |                avg |
|----|------------|--------|---------|------|------|--------------------|
|  1 | 2018-01-01 | PLANTA | VENDORA |  OPA |    1 |  4.166666666666667 |
|  2 | 2018-02-01 | PLANTA | VENDORA |  OPA |    1 |  4.166666666666667 |
|  3 | 2018-03-01 | PLANTA | VENDORA |  OPA |    1 |  4.166666666666667 |
|  4 |     (null) | PLANTA | VENDORA |  OPA |    1 |  4.166666666666667 |
|  5 | 2018-10-01 | PLANTA | VENDORA |  OPA |    5 |  4.166666666666667 |
|  6 | 2018-10-01 | PLANTA | VENDORA |  OPA |   10 |  4.166666666666667 |
|  8 | 2018-10-01 | PLANTA | VENDORA |  OPA |   10 |  4.166666666666667 |
|  9 | 2018-11-01 | PLANTA | VENDORA |  OPB |    5 | 0.8333333333333334 |
|  7 | 2018-11-01 | PLANTA | VENDORB |  OPA |   50 |  8.333333333333334 |

[演示：db <> fiddle] [4]

使用window function SUM(...) OVER (PARTITION BY ...)可以像在GROUP子句中一样进行SUM聚合，但保留原始行。聚合将添加为单独的列。
FILTER子句允许您过滤聚合函数的输入。因此，您只能汇总datum >= ...

Answer 2

为什么不只将条件移至where子句：

SELECT   cola, colb, colc, SUM(cold) / 6
FROM     testAAA
WHERE    datum >= NOW() - INTERVAL '6 MONTH' 
GROUP BY cola, colb, colc

根据条件的平均金额

2 个答案: