Will Noble created CALCITE-5767:
-----------------------------------
Summary: MSSQL fails to unparse properly when sorting by GROUPING
expression
Key: CALCITE-5767
URL: https://issues.apache.org/jira/browse/CALCITE-5767
Project: Calcite
Issue Type: Bug
Components: core
Reporter: Will Noble
In {{{}RelBuilder.collation{}}}, we use the "default null direction" to insert
rex nodes as sorting expressions, but this is only the default null direction
for NULLS-high dialects, i.e. *not* MSSQL. This is a problem because MSSQL has
special-case logic for emulating null direction of GROUPING calls, whereby it
effectively duplicates the expression. Really,
{{MssqlSqlDialect.emulateNullDirection}} probably should've been returning
{{null}} instead, signalling to callers that no null-direction emulation is
necessary because {{GROUPING}} never returns {{{}NULL{}}}, but this causes
another problem when the null direction is non-default as is caused simply by
using {{RelBuilder.collation}} as described above (it should be noted that this
method takes rex nodes instead of {{RelFieldCollation}} object, so there is no
way to specify null direction) because the non-default null direction is not
expanded into a {{CASE}} expression (MSSQL does not support {{NULLS FIRST}} or
{{LAST}} syntax).
Here's a test illustrating the problem:
Input SQL (default dialect)
{code:xml}
select "product_class_id", "brand_name", GROUPING("brand_name")
from "product"
group by GROUPING SETS (("product_class_id", "brand_name"),
("product_class_id"))
order by 3, 2, 1
{code}
Current behavior for unparsing as MSSQL (incorrect because it orders by the
same column twice; {{GROUPING([brand_name])}} and {{3}}):
{code:xml}
SELECT [product_class_id], [brand_name], GROUPING([brand_name])
FROM [foodmart].[product]
GROUP BY GROUPING SETS(([product_class_id], [brand_name]), [product_class_id])
ORDER BY
GROUPING([brand_name]),
3,
CASE WHEN [brand_name] IS NULL THEN 1 ELSE 0 END,
[brand_name],
CASE WHEN [product_class_id] IS NULL THEN 1 ELSE 0 END,
[product_class_id]
{code}
Behavior where {{MssqlSqlDialect.emulateNullDirection}} simply returns {{null}}
for {{GROUPING}} expressions (incorrect because it uses {{NULLS LAST}} syntax):
{code:xml}
...
ORDER BY
3 NULLS LAST,
3,
CASE WHEN [brand_name] IS NULL THEN 1 ELSE 0 END,
[brand_name],
CASE WHEN [product_class_id] IS NULL THEN 1 ELSE 0 END,
[product_class_id]
{code}
Acceptable behavior:
{code:xml}
...
ORDER BY
CASE WHEN GROUPING([brand_name]) IS NULL THEN 0 ELSE 1 END,
3,
CASE WHEN [brand_name] IS NULL THEN 1 ELSE 0 END,
[brand_name],
CASE WHEN [product_class_id] IS NULL THEN 1 ELSE 0 END,
[product_class_id]
{code}
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
