BLOB fields did not work as grouping keys at all, they were assigned
value NULL for any value, be it NULL or not. The fix is in the
rowaggregation.cpp in the initMapping(), a switch/case branch was added
to handle BLOB field copying there.
Also, TEXT columns did not distinguish between NULL and empty string in
the grouping algorithm, now they do. The fix is in the equals()
function, now we specifically check for isNull() equality between
values.
This patch improves handling of NULLs in textual fields in ColumnStore.
Previously empty strings were considered NULLs and it could be a problem
if data scheme allows for empty strings. It was also one of major
reasons of behavior difference between ColumnStore and other engines in
MariaDB family.
Also, this patch fixes some other bugs and incorrect behavior, for
example, incorrect comparison for "column <= ''" which evaluates to
constant True for all purposes before this patch.
in aggregation code
The patch disables padding that forces hasher to calculate over the whole 2k buffer. This patch also moves hashing code
into the common place where it belongs.
This change fixes:
MCOL-4462 CAST(varchar_expr AS DECIMAL(M,N)) returns a wrong result
MCOL-4500 Bit functions processing throws internally trying to cast char into decimal representation
MCOL-4532 CAST(AS DECIMAL) returns a garbage for large values
Also, this change makes string-to-decimal conversion 5-10 times faster,
depending on exact data.
Performance implemenent is achieved by the fact that (unlike in the old
implementation), the new version does not do any "string" object copying.
A non-JOIN condition like `WHERE c1=c2` (with c1 and c2 being columns of the
same table) was not collation-aware yet after the main patches for MCOL-4064.
Additionally fixing StrFilterCmd::compare*() to address this.
