atris opened a new issue #8060:
URL: https://github.com/apache/pinot/issues/8060
This issue tracks the development of the feature that brings multiple
grouping sets to Pinot.
**What is A Grouping Set?**
Consider the following query:
```
SELECT
brand,
segment,
SUM (quantity)
FROM
sales
GROUP BY
brand,
segment;
```
(brand, segment) represents a single grouping set.
A query using multiple grouping sets would be represented as:
```
SELECT
c1,
c2,
aggregate_function(c3)
FROM
table_name
GROUP BY
GROUPING SETS (
(c1, c2),
(c1),
(c2),
()
);
```
An equivalent query using UNION ALL would be:
```
SELECT
brand,
segment,
SUM (quantity)
FROM
sales
GROUP BY
brand,
segment
UNION ALL
SELECT
brand,
NULL,
SUM (quantity)
FROM
sales
GROUP BY
brand
UNION ALL
SELECT
NULL,
segment,
SUM (quantity)
FROM
sales
GROUP BY
segment
UNION ALL
SELECT
NULL,
NULL,
SUM (quantity)
FROM
sales;
```
GROUPING SETS also allows empty sets () which is equivalent of SELECT * FROM
foo;
**CUBE and ROLLUP**
`CUBE(c1, c2, c3) ` generates:
```
(c1, c2, c3)
(c1, c2)
(c2, c3)
(c1,c3)
(c1)
(c2)
(c3)
()
```
`ROLLUP(c1, c2,c3)` generates:
```
(c1, c2, c3)
(c1, c2)
(c1)
()
```
ROLLUP generates groups in hierarchy vs. CUBE generating all groups.
**Design**
A design document shall soon be published but the design theme will be to
use the swim lane concept introduced in the FILTER PR. An important design goal
is to avoid rescans.
`Implementation Plan`
The implementation plan will be to first support ROLLUP, then CUBE and then
generic GROUPING sets.
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