获取 ROLLUP 以包含缺失值的行

Question

PostgreSQL 14

假设此示例数据：

fruit	ripeness
orange	1
orange	3
apple	0
apple	3
apple	3
apple	2

有没有办法让 ROLLUP 按成熟度为我提供水果数量，并为每个可能的成熟度值排成一行，如下所示：

fruit	ripeness	count
orange	0	0
orange	1	1
orange	2	0
orange	3	1
orange		2
apple	0	1
apple	1	0
apple	2	1
apple	3	2
apple		4
		6

而不是像这样仅显示组中的现有值：

fruit	ripeness	count
orange	1	1
orange	3	1
orange		2
apple	0	1
apple	2	1
apple	3	2
apple		4
		6

Answer 1

将 fruit 的不同值交叉连接到 ripeness 的不同值，并对 table.
进行 LEFT 连接然后聚合 ROLLUP:

SELECT f.fruit, r.ripeness, 
       COUNT(t.fruit) counter
FROM (SELECT DISTINCT fruit FROM tablename) f
CROSS JOIN (SELECT DISTINCT ripeness FROM tablename) r
LEFT JOIN tablename t ON t.fruit = f.fruit AND t.ripeness = r.ripeness
GROUP BY ROLLUP(f.fruit, r.ripeness)
ORDER BY f.fruit, r.ripeness;

参见demo。

Answer 2

没有ROLLUP的解决方案，天真但直观：

select * from (
  (
    select distinct f1.fruit, f2.ripeness, (
        select count(1) from fruit fsq where
            f1.fruit = fsq.fruit and
            f2.ripeness = fsq.ripeness
    ) from fruit f1
    left join fruit f2 on true
    group by f1.fruit, f2.ripeness
  )
  union
  (
  select fruit.fruit, null, count(1) from fruit
    group by fruit.fruit
  )
  union
  (
  select null, null, count(1) from fruit
  )
) mq
order by 1, 2;

Demo.

获取 ROLLUP 以包含缺失值的行

Get ROLLUP to include rows for missing values

postgresql

group-by

rollup

left-join

cross-join