Mysql返回多行答案

【问题标题】：Mysql return more than one rowMysql返回多行
【发布时间】：2012-06-06 17:18:56
【问题描述】：

我有这个问题。

SELECT notes.id,enter.name as 'enter_name',step.title as 'flow status',notes.user_name as user_created,notes.created,notes.rel_client_id,td_doc_nr.value_string as 'document number',enter.enter_code,
    IF(!ISNULL(td_doc_nr.value_string),
     (SELECT  GROUP_CONCAT(product_name SEPARATOR ',') from notes d 
        join note_bundles b on b.note_id = d.id
        join note_products p on p.doc_bundle_id = b.id
        join note_product_get_fields f on f.doc_product_id = p.id
        join note_product_get_field_data fd on fd.get_field_id = f.id
        where d.doc_nr = td_doc_nr.value_string
        and value_string ='auto')
,NULL) as test
FROM notes notes
JOIN notes_steps step ON  step.id  = notes.step_id 
JOIN notes_enters enter ON enter.id = notes.enter_id
    LEFT JOIN notes_custom_fields tf_doc_nr ON tf_doc_nr.name = 'note_number' AND tf_doc_nr.rel_entity_id = enter.id
    LEFT JOIN notes_custom_field_data td_doc_nr ON td_doc_nr.rel_entity_id = notes.id AND
 td_doc_nr.field_instance_id = tf_doc_nr.id 
WHERE notes.enter_id in  (777) AND notes.status = 1

我将此子查询添加到“if 语句”中

 SELECT  GROUP_CONCAT(product_name SEPARATOR ',') from nontes d 
    join note_bundles b on b.note_id = d.id
    join note_products p on p.doc_bundle_id = b.id
    join note_product_get_fields f on f.doc_product_id = p.id
    join note_product_get_field_data fd on fd.get_field_id = f.id
    where d.doc_nr = 'G7777777'
    and value_string ='auto'

在此之后我添加了一个新列。

 SELECT  GROUP_CONCAT(product_name SEPARATOR ','),GROUP_CONCAT(DISTINCT b.msisdn SEPARATOR ',') from notes d 
    join note_bundles b on b.note_id = d.id
    join note_products p on p.doc_bundle_id = b.id
    join note_product_get_fields f on f.doc_product_id = p.id
    join note_product_get_field_data fd on fd.get_field_id = f.id
    where d.doc_nr = 'G7777777'
    and value_string ='auto'

它返回两列。我怎样才能返回两列？有可能吗？ :) 谢谢

【问题讨论】：

我不确定我是否理解这个问题。请您提供示例输入数据，以及您希望输出数据是什么？
所以你想返回两列并且你返回两列。有什么问题？
我不认为您可以使用子查询返回多个字段。如果您想要快速修复，只需将查询复制两次即可。
@afuzzyllama 我考虑过了..还是谢谢。

标签： mysql sql group-concat

【解决方案1】：

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

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

【讨论】：

【解决方案2】：

IF 语句中的相关子查询只能返回 1 列和 1 行，这就是您收到错误的原因。但是，查看您的查询，子查询中唯一的外部引用是

d.doc_nr = td_doc_nr.value_string

因此，您实际上不需要相关子查询，您可以通过将子查询移动到联接并在子查询中按 doc_nr 分组来获得相同的结果，这可能会更有效，并且允许您返回您想要的 2 列：

SELECT  tickets.id,
        source.name as 'source_name',
        flow_stage.title as 'flow status',
        tickets.user_name as user_created,
        tickets.created,
        tickets.rel_client_id,
        td_doc_nr.value_string as 'document number',
        source.source_code,
        IF(!ISNULL(td_doc_nr.value_string), ProductNames, NULL) as test,
        d.MSISDNS
FROM    tickets tickets
        JOIN tickets_flow_stages flow_stage 
            ON flow_stage.id  = tickets.flow_stage_id 
        JOIN tickets_sources source 
            ON source.id = tickets.source_id
        LEFT JOIN tickets_custom_fields tf_doc_nr 
            ON tf_doc_nr.name = 'document_number' 
            AND tf_doc_nr.rel_entity_id = source.id
        LEFT JOIN tickets_custom_field_data td_doc_nr 
            ON td_doc_nr.rel_entity_id = tickets.id 
            AND td_doc_nr.field_instance_id = tf_doc_nr.id 
        LEFT JOIN
        (   SELECT  d.Doc_nr,
                    GROUP_CONCAT(product_name SEPARATOR ',') AS ProductNames,
                    GROUP_CONCAT(DISTINCT b.msisdn SEPARATOR ',') AS MSISDNS
            from    documents d 
                    INNER JOIN document_bundles b 
                        ON b.document_id = d.id
                    INNER JOIN document_products p 
                        ON p.doc_bundle_id = b.id
                    INNER JOIN document_product_cstm_fields f 
                        ON f.doc_product_id = p.id
                    INNER JOIN document_product_cstm_field_data fd 
                        ON fd.cstm_field_id = f.id
            WHERE   value_string ='auto'
            GROUP BY d.Doc_nr
        ) d
            ON d.doc_nr = td_doc_nr.value_string
WHERE   tickets.source_id IN (114,122,125,129,131) 
AND     tickets.status = 1

【讨论】：