Handle Num and Rat as MYSQL_TYPE_DOUBLE

This matches the behaviour of the perl DBD::mysql driver.

The test confirms that the fields are created as "double", and that strings which look like numbers remain a string.

lib/DBDish/mysql/StatementHandle.rakumod

@@ -116,6 +116,13 @@ method execute(*@params --> DBDish::StatementHandle) {
                     @Bufs[$k] = do {
                         when Blob { $st = MYSQL_TYPE_BLOB; $_ }
                         when Str  { .encode }
+                        when Rat | Num {
+                            # This may be lossy for very large values.
+                            $st = MYSQL_TYPE_DOUBLE;
+                            my $buf = buf8.new();
+                            $buf.write-num64(0, $_.Num);
+                            $buf;
+                        }
                         when Int  {
                             # Handle anything larger than int64 as a string.
                             if -2**63 <= $_ <= 2**63 -1 {

t/24-mysql-types.t

@@ -0,0 +1,26 @@
+use v6;
+use Test;
+use DBIish::CommonTesting;
+
+plan 1;
+my %con-parms = :database<dbdishtest>, :user<testuser>, :password<testpass>;
+%con-parms<host> = %*ENV<MYSQL_HOST> if %*ENV<MYSQL_HOST>;
+my $dbh = DBIish::CommonTesting.connect-or-skip('mysql', |%con-parms);
+
+subtest 'Num and Rat are numbers' => {
+    $dbh.execute('CREATE TEMPORARY TABLE tmp_num_test AS SELECT ? as num, ? as rat, ? as unspecified',
+            2.0.Num, 2.0.Rat, 2.0);
+
+    my $sth = $dbh.execute('describe tmp_num_test');
+    while my $row = $sth.row {
+        my ($col-name, $datatype-buf) = $row;
+        my $datatype = $datatype-buf.decode;
+        is $datatype, 'double', "$col-name type is double";
+    }
+
+    $sth = $dbh.execute('SELECT * FROM tmp_num_test');
+    my ($num, $rat, $unspecified, $string) = $sth.row;
+    is $num, 2.0.Num, 'Num value roundtriped';
+    is $rat, 2.0.Rat, 'Rat value roundtriped';
+    is $unspecified, 2.0.Num, 'Unspecified was treated as Num';
+}