presto-base-jdbc/src/main/java/io/prestosql/plugin/jdbc/BaseJdbcClient.java/BaseJdbcClient/getForcedMappingToVarchar
class BaseJdbcClient:    protected Optional<ColumnMapping> getForcedMappingToVarchar(JdbcTypeHandle typeHandle)
    {
        if (typeHandle.getJdbcTypeName().isPresent() && jdbcTypesMappedToVarchar.contains(typeHandle.getJdbcTypeName().get())) {
            return Optional.of(ColumnMapping.sliceMapping(
                    createUnboundedVarcharType(),
                    varcharReadFunction(),
                    varcharWriteFunction(),
                    DISABLE_PUSHDOWN));
        }
        return Optional.empty();
    }