如果子查询在 Postgres 中返回多行，则跳过行

Question

我想prod_replay_out根据 Postgres 中的子查询结果更新表。但是，子查询返回多行，但我想跳过这些行并根据子查询返回的单行更新表。

我已经提到链接子查询返回超过 1 行错误，但max()函数不适用于我的预期结果。您能否为我提供一些修改查询的建议？谢谢你。

prod_replay_out 有以下列：

卖家、买家、sender_tag、seller_tag、买家标签、isin、数量、in_msg_time、msg_type、cdsx_time

prod_replay_in 有以下列：

卖家、买家、sender_tag、seller_tag、买家标签、isin、数量、msg_type、cdsx_time

我尝试过什么？

请在下面找到更新sql：

更新sql：

update prod_replay_out O  
   set in_msg_id = 
        (Select id
           From prod_replay_in I
          Where I.msg_type   = 'CDST010'
            and I.seller     = O.seller
            and I.buyer      = O.buyer
            and I.sender_tag = O.sender_tag
            and I.seller_tag = O.seller_tag
            and I.buyer_tag  = O.buyer_tag
            and I.isin       = O.isin
            and I.quantity   = O.quantity
            and I.cdsx_time  = O.in_msg_time
            and I.cdsx_time::text like '2020-05-12%'
         ) 
where O.msg_type = 'CDST01C'
and O.cdsx_time::text like '2020-05-12%';

我尝试了以下解决方案。这是正确的方法还是有什么漏洞？

update prod_replay_out O  
   set in_msg_id = 
        (Select id
           From prod_replay_in I
          Where I.msg_type   = 'CDST010'
            and I.seller     = O.seller
            and I.buyer      = O.buyer
            and I.sender_tag = O.sender_tag
            and I.seller_tag = O.seller_tag
            and I.buyer_tag  = O.buyer_tag
            and I.isin       = O.isin
            and I.quantity   = O.quantity
            and I.cdsx_time  = O.in_msg_time
            and I.cdsx_time::text like '2020-05-12%'
            and 1 = (Select count(id)
                       From prod_replay_in I
                      Where I.msg_type   = 'CDST010'
                        and I.seller     = O.seller
                        and I.buyer      = O.buyer
                        and I.sender_tag = O.sender_tag
                        and I.seller_tag = O.seller_tag
                        and I.buyer_tag  = O.buyer_tag
                        and I.isin       = O.isin
                        and I.quantity   = O.quantity
                        and I.cdsx_time  = O.in_msg_time
                        and I.cdsx_time::text like '2020-05-12%'
                    )    
                )
where O.msg_type = 'CDST01C'
  and O.cdsx_time::text like '2020-05-12%';

Answer 1

您只想在子查询返回一行时更新。一种选择是having在子查询中使用聚合和：

update prod_replay_out o  
set in_msg_id = (
    select max(id)
    from prod_replay_in i
    where 
        i.msg_type       = 'cdst010'
        and i.seller     = o.seller
        and i.buyer      = o.buyer
        and i.sender_tag = o.sender_tag
        and i.seller_tag = o.seller_tag
        and i.buyer_tag  = o.buyer_tag
        and i.isin       = o.isin
        and i.quantity   = o.quantity
        and i.cdsx_time  = o.in_msg_time
        and i.cdsx_time  >= '2020-05-12'::date
        and i.cdsx_time  <  '2020-05-13'::date
    having count(*) = 1
) 
where 
    o.msg_type = 'cdst01c'
    and o.cdsx_time  >= '2020-05-12'::date
    and o.cdsx_time  <  '2020-05-13'::date
    

请注意，我重写了日期过滤器，以避免转换为文本（您可以使用带有日期文字的半开区间，这样效率更高）。

请注意，这会更新in_msg_id到null子查询返回多行（或根本没有行）的情况。如果你想避免这种情况，你可以在where子句中进行过滤：

update prod_replay_out o  
set in_msg_id = (
    select max(id)
    from prod_replay_in i
    where 
        i.msg_type       = 'cdst010'
        and i.seller     = o.seller
        and i.buyer      = o.buyer
        and i.sender_tag = o.sender_tag
        and i.seller_tag = o.seller_tag
        and i.buyer_tag  = o.buyer_tag
        and i.isin       = o.isin
        and i.quantity   = o.quantity
        and i.cdsx_time  = o.in_msg_time
        and i.cdsx_time  >= '2020-05-12'::date
        and i.cdsx_time  <  '2020-05-13'::date
    having count(*) = 1
) 
where 
    o.msg_type = 'cdst01c'
    and o.cdsx_time  >= '2020-05-12'::date
    and o.cdsx_time  <  '2020-05-13'::date
    and (
        select count(*)
        from prod_replay_in i
        where 
            i.msg_type       = 'cdst010'
            and i.seller     = o.seller
            and i.buyer      = o.buyer
            and i.sender_tag = o.sender_tag
            and i.seller_tag = o.seller_tag
            and i.buyer_tag  = o.buyer_tag
            and i.isin       = o.isin
            and i.quantity   = o.quantity
            and i.cdsx_time  = o.in_msg_time
            and i.cdsx_time  >= '2020-05-12'::date
            and i.cdsx_time  <  '2020-05-13'::date
    ) = 1