# MySql Usage Notes

## Unsigned Fields

MySql supports both signed, and unsigned, numeric fields. These are not JDBC types, so MyBatis generator cannot automatically account for these types of fields. The Java data types are always signed. This can lead to a loss of precision when using unsigned fields. The solution is to provide a `<columnOverride>` for any unsigned numeric field in MySql. Here is an example of how to deal with an unsigned bigint field in MySql:

      <table tableName="ALLTYPES" >
        <columnOverride column="UNSIGNED_BIGINT_FIELD" javaType="java.lang.Object" jdbcType="LONG" />
      </table>

You will have to cast the returned value to the appropriate type yourself (in this case, `java.math.BigInteger`).