In the file https://github.com/mariadb-corporation/mariadb-connector-odbc/blob/master/ma_string.c there a two lines who contradict each other:
On https://github.com/mariadb-corporation/mariadb-connector-odbc/blob/852f63465b03045dba73cc36fc5710aea0f55b5c/ma_string.c#L213 the int variable Flag is created with an initial value of 0 and in https://github.com/mariadb-corporation/mariadb-connector-odbc/blob/852f63465b03045dba73cc36fc5710aea0f55b5c/ma_string.c#L257 the condition is true if the Flag value is 0, which is always the case, since the Flag value never changes after initialization.

As far as i can tell the value of flag should depend on the values of PrimaryCount and/or UniqueCount, to avoid to compare all columns and not just the primary key/unique columns.

A quick fix is to set the value of Flag prior to the for loop (line 262):

...

if(PrimaryCount)

{

    Flag = PRI_KEY_FLAG;

}

else if(UniqueCount) 

{

    Flag = UNIQUE_KEY_FLAG;

}

for (i= 0; i < MADB_STMT_COLUMN_COUNT(Stmt); i++)

{

...

I have attached a "corrected" version of ma_string.c for comparison.