presto-mysql/src/main/java/io/prestosql/plugin/mysql/MySqlClient.java/MySqlClient/toPrestoType
class MySqlClient:    @Override
    public Optional<ColumnMapping> toPrestoType(ConnectorSession session, Connection connection, JdbcTypeHandle typeHandle)
    {
        String jdbcTypeName = typeHandle.getJdbcTypeName()
                .orElseThrow(() -> new PrestoException(JDBC_ERROR, "Type name is missing: " + typeHandle));

        Optional<ColumnMapping> mapping = getForcedMappingToVarchar(typeHandle);
        if (mapping.isPresent()) {
            return mapping;
        }
        if (jdbcTypeName.equalsIgnoreCase("json")) {
            return Optional.of(jsonColumnMapping());
        }
        return super.toPrestoType(session, connection, typeHandle);
    }