IF语句中的子查询不能返回多列.您将需要将子查询加入结果中，并分别拉出两个单独的列:

A subquery inside an IF statement can't return multiple columns. You will need to join the subquery into the results, and pull out the two separate columns individually:

SELECT ...
    IF(!ISNULL(td_doc_nr.value_string), sub.one, NULL) as one,
    IF(!ISNULL(td_doc_nr.value_string), sub.two, NULL) as two
FROM ...
LEFT JOIN (
    SELECT  d.doc_nr, GROUP_CONCAT(product_name SEPARATOR ','),GROUP_CONCAT(DISTINCT b.msisdn SEPARATOR ',') from documents d 
    join document_bundles b on b.document_id = d.id
    join document_products p on p.doc_bundle_id = b.id
    join document_product_cstm_fields f on f.doc_product_id = p.id
    join document_product_cstm_field_data fd on fd.cstm_field_id = f.id
    where value_string ='auto'
    group by d.doc_nr
) sub on sub.doc_nr = td_doc_nr.value_string