Question

我有两个文件：apt和appointment_history。第二个文件有多个在apt中引用单个记录的记录。

如何仅从子查询中获取引用apt中记录的约会历史记录中的最后一条记录？

编辑＃1：问题不在于如何分组，而在于如何将外部值（appointment_recid）传递到子查询中，而不将整个appointment_history文件分组到未使用的appointment_recid上。所以我不认为这是一个重复的问题。（虽然是一个noobie，它可能会变成相同的。）

PostgreSQL 9.3

错误：对表＆＃34; apt＆＃34;的FROM子句条目的无效引用SQL state：42P01提示：表＆＃34; apt＆＃34;有一个条目，但它不能从查询的这一部分引用。

git

TIA

Answer 1

select apt.*, h.* 
    from apt 
    join appointment_history h 
      on (h.appointment_recid = apt.appointment_recid)
    join ( 
           SELECT appointment_recid, max(tposted) as tposted 
           FROM appointment_history a
           GROUP BY  appointment_recid  -- ADD GROUP BY 
         ) currenthx 
      on currenthx.tposted = h.tposted
     and currenthx.appointment_recid = a.appointment_recid   -- JOIN OUTSIDE

请求

select apt.*, h.* 
    from apt 
    join appointment_history h 
      on (h.appointment_recid = apt.appointment_recid)
    join ( 
           SELECT appointment_recid, max(tposted) as tposted 
           FROM appointment_history a
           JOIN apt ap
               on (h.appointment_recid = ap.appointment_recid)               
           GROUP BY  appointment_recid  -- ADD GROUP BY 
         ) currenthx 
      on currenthx.tposted = h.tposted
     and currenthx.appointment_recid = a.appointment_recid   -- JOIN OUTSIDE

Answer 2

如果没有详细的表格信息，这可能会解决您的问题：

SELECT apt.*, h.* 
FROM apt
JOIN (
  SELECT <columns>, max(tposted) AS tposted 
  FROM appointment_history
  GROUP BY <columns>) h USING (appointment_recid);

如何将记录值传递给子查询（PostgreSQL）？

2 个答案: