This patch introduces an internal aggregate operator SELECT_SOME that
is automatically added to columns that are not in GROUP BY. It
"computes" some plausible value of the column (actually, last one
passed).
Along the way it fixes incorrect handling of HAVING being transferred
into WHERE, window function handling and a bit of other inconsistencies.
* MCOL-4234: improve GROUP BY and ORDER BY interaction (#3194)
This patch fixes the problem in MCOL-4234 and also generally improves
behavior of GROUP BY.
It does so by introducing a "dummy" aggregate and by wrapping columns
into it. This allows for columns that are not in GROUP BY to be used
more freely, for example, in SELECT * FROM tbl GROUP BY col - all
columns that are not "col" will be wrapped into an aggregate and query
will proceed to execution.
The dummy aggregate itself does nothing more than remember last value
passed into it.
There also an additional error message that tries to explain what types
of expressions can be wrapped into an aggregate.
* MCOL-5772: incorrect ORDER BY ordering for a columns not in GROUP BY (#3214)
When ORDER BY column is not in GROUP BY, is not an aggregate and there
is a SELECT column that is also not an aggregate, there was a problem:
ordering happened on the SELECTed column, not ORDERed one.
This patch fixes that particular problem and also performs some tidying
around newly added aggregate.
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Co-authored-by: Leonid Fedorov <79837786+mariadb-LeonidFedorov@users.noreply.github.com>
