如何使用另一个表 B 中的值更新表 A 中的列，其中表 A 和 B 之间的关系是 1：N，使用 max() 函数

Question

我有两个表，即 loan_details 和 loan_his_mapping 与 1:N 关系。我需要通过 loan_his_mapping 表中每个贷款的值来设置 loan_details 表的 hhf_request_id。

由于关系是 1:N ，我想考虑 loan_his_mapping 表中每笔贷款的记录，并具有以下两个条件。表定义如下：

   CREATE TABLE public.loan_details 
 (
       loan_number   bigint NOT NULL,
        hhf_lob     integer,
        hhf_request_id   integer,
        status  character varying(100),
         CONSTRAINT loan_details_pkey PRIMARY KEY (loan_number)
     );


             CREATE TABLE public.loan_his_mapping
          (
               loan_number           bigint NOT NULL,
                spoc_id               integer NOT NULL,
               assigned_datetime     timestamp without time zone,
               loan_spoc_map_id bigint NOT NULL,
                line_of_business_id   integer,
                request_id bigint,
          CONSTRAINT loan_spoc_his_map_id PRIMARY KEY (loan_spoc_map_id),
          CONSTRAINT fk_loan_spoc_loan_number_his FOREIGN KEY (loan_number)
         REFERENCES public.loan_details (loan_number) MATCH SIMPLE
          ON UPDATE NO ACTION ON DELETE NO ACTION );

更新时的加入条件为：

1. hhf_lob = 4和status='Release'的loan_details记录
2. 我应该考虑使用该记录来更新 loan_his_mapping 表中的“N”条记录中的值，每笔贷款的值为 ma​​x(loan_spoc_map_id)。

我现在的查询

 update lsa_loan_details ldet
 set hhf_request_id = history.request_id 
 from loan_his_mapping history  
 where ldet.loan_number = history.loan_number and ldet.status='Release' and  ldet.hhf_lob=4 and 
 history.line_of_business_id=4 ;

我想知道如何使用 loan_his_mapping 和 ma​​x(loan_spoc_map_id) 的每笔贷款的记录来更新 loan_details 的列强>表。请帮忙！

Answer 1

你需要一个子查询来获取最高loan_spoc_map_id对应的行

类似的东西：

update loan_details ldet
   set hhf_request_id = history.request_id 
from (
  select distinct on (loan_spoc_map_id) loan_number, request_id
  from loan_his_mapping  lhm
  where lhm.line_of_business_id = 4
  order by loan_spoc_map_id desc
) as history  
where ldet.loan_number = history.loan_number 
  and ldet.status = 'Release' 
  and ldet.hhf_lob = 4;