mysqli_native_moodle_database.php has this:

public function sql_cast_char2real($fieldname, $text=false) {

    return ' CAST(' . $fieldname . ' AS DECIMAL) ';

}

This isn't great as when casting to DECIMAL in MySQL we need to specify precision and scale. Where precision represents how many digits there are in total and scale specifies how many fractional digits there are. This is done with DECIMAL(M,D) where M is precision and D is decimal places. When M and D aren't specified, the default is DECIMAL(M, 0) where M refers to how many digits are in the string total

SELECT CAST('9999.9' as DECIMAL)); //equivalent to DECIMAL(5)

+---------+

| Decimal |

+---------+

|   10000 |

+---------+

SELECT CAST('9999.9' as DECIMAL(4)));

+---------+

| Decimal |

+---------+

|    9999 |

+---------+

SELECT CAST('9999.9' as DECIMAL(5,1)) as 'Decimal';

+---------+

| Decimal |

+---------+

|  9999.9 |

+---------+