[hibernate-dev] MySQL versus MariaDB

[Steve Ebersole]

As I have developed the matrix tests against MariaDB I have had in the back
of my head whether we might want to develop a Dialect for MariaDB.  As I
understand it, MariaDB does strive to remain compatible with MySQL but it
does offer some enhancements.  And it might have some minor deviations.
Today I think I found one such deviation, in their respective support for
casting decimal/floating-point values.  I came across this because of some
failed tests.

There are quite a few resolved issues in Jira wrt MySQL and casting.  So I
have to assume these tests work on MySQL which tells me there is a
deviation in their behavior...

The tests in question (more or less) do: "select ... cast( x as big_decimal
) ...".  We understand big_decimal as java.sql.Types#NUMERIC for which the
MySQL Dialect says to use "decimal" for casting purposes.

On MariaDB at least "decimal" (no precision) leads to a data trunction.  We
are expecting a value like "12.399999618530273" but get back "12.0".
Because for MariaDB DECIMAL is equivalent to DECIMAL(10,0).

So as it is, for this minor case at least the MySQL dialects work against
MySQL databases (we assume) but fail against MariaDB databases.

The other difficulty with a dialect specific for MariaDB is
auto-detection.  The MariaDB JDBC drivers report the underlying database as
mysql.