QA:
This bug has only been observed for regr_avgx and regr_avgy. Bad = unlimited (random) number of decimal points. Good = fixed decimal equal to the number of decimals in the argument + 4.

Example:
MariaDB [tpch1]> select avg(l_extendedprice), l_tax, regr_avgx(l_tax, l_extendedprice) from lineitem group by l_tax order by l_tax;
------------------------------------------------------------

------------------------------------------------------------

------------------------------------------------------------
9 rows in set (1.282 sec)

Note that the number of decimals for AVG and REGR_AVGX are 6, which is the two from l_extendedprice + 4. Before this patch AVG and REGR_AVGX would be different, with AVG being correct, but REGR_AVGX with possibly many more decimal places.

This did not affect 1.2, but is a regression due to convergence.

Similarly for REGR_AVGY:
MariaDB [tpch1]> select avg(l_extendedprice), l_tax, regr_avgy(l_tax, l_extendedprice) from lineitem group by l_tax order by l_tax;
------------------------------------------------------------

------------------------------------------------------------

------------------------------------------------------------
9 rows in set (1.260 sec)

This takes the AVG of the Y (first) parameter. SInce l_tax has 2 decimal places defined, the result should have 6 decimal places.

Build tested: 1.4.1-1

[dlee@master tests]$ cat /data/qa/release/1.4.1-1/centos7/gitversionInfo.txt
engine commit:
3e7a964

When trying to run queries, I hit the following error:

select avg(l_extendedprice), l_tax, regr_avgx(l_tax, l_extendedprice) from lineitem group by l_tax order by l_tax;
ERROR 1305 (42000): FUNCTION tpch1.regr_avgx does not exist

I think this is the same issue as reported in other bugs. I will test again when the issue is fixed.

Build verfied: 1.4.1-1 github source

Server
commit 77a245fe5658b8d6d937620586ecd802b3432a78
Author: Marko Mäkelä <marko.makela@mariadb.com>
Date: Sun Nov 17 20:04:11 2019 +0200

Engine
commit 7c6a086cfb54b8bbd500efb41f34c9fa1ed03ca1
Merge: f291d88 1a94d53
Author: Roman Nozdrin <drrtuy@gmail.com>
Date: Mon Nov 18 12:11:30 2019 +0300

MariaDB [tpch1]> select avg(l_extendedprice), l_tax, regr_avgx(l_tax, l_extendedprice) from lineitem group by l_tax order by l_tax;
------------------------------------------------------------

------------------------------------------------------------

------------------------------------------------------------
9 rows in set (1.298 sec)

MariaDB [tpch1]> select avg(l_extendedprice), l_tax, regr_avgy(l_tax, l_extendedprice) from lineitem group by l_tax order by l_tax;
------------------------------------------------------------

------------------------------------------------------------

------------------------------------------------------------
9 rows in set (1.220 sec)