Question

我有两个问题。第一个 -

SELECT
  communications.creation_date as message_date, 
  message as message_text, 
  employees.first_name || ' ' || coalesce(employees.middle_name,'') || ' ' || employees.last_name as message_by
FROM app.communications 
INNER JOIN app.employees ON communications.message_from = employees.emp_id 
WHERE send_as_sms = TRUE AND com_id = (SELECT MAX(com_id) FROM app.communications)

基本上输出 - | message_date | message_text | message_by |

第二个查询 -

SELECT
  cs.com_id, 
  cs.first_name ||' ' || cs.last_name AS recipient_name, 
  cs.sim_number AS phone_number
FROM app.communication_sms cs
WHERE cs.com_id = (SELECT MAX(cs2.com_id) FROM app.communication_sms cs2)
ORDER BY first_name ASC

输出 - | com_id | recipient_name | phone_number |

从查询中可以看出，两个表都有一个"com_id"列。我需要的是制作一个单独的查询，它将合并上面的两个查询以获得单个输出，如 -

我怎样才能实现这一目标？由于数据类型和列数不同，我无法使用UNION。我很感激你的帮助。

Answer 1

不确定com_id是否相等，但如果它们可能不相同，那么我建议：

select * -- list out the columns, I haven't bothered here
FROM (
      SELECT MAX(com_id) as com_id FROM app.communications 
      UNION
      SELECT MAX(cs2.com_id) FROM app.communication_sms cs2
      ) u
left join (
      SELECT
        com_id -- don't know which table this comes from
        communications.creation_date as message_date, 
        message as message_text, 
        employees.first_name || ' ' || coalesce(employees.middle_name,'') || ' ' || employees.last_name as message_by
      FROM app.communications 
      INNER JOIN app.employees ON communications.message_from = employees.emp_id 
      WHERE send_as_sms = TRUE AND com_id = (SELECT MAX(com_id) FROM app.communications)
     ) s1 on u.com_id = s1.com_id
left join (
SELECT
        cs.com_id, 
        cs.first_name ||' ' || cs.last_name AS recipient_name, 
        cs.sim_number AS phone_number
      FROM app.communication_sms cs
      WHERE cs.com_id = (SELECT MAX(cs2.com_id) FROM app.communication_sms cs2)
      ORDER BY first_name ASC
      ) s2 on u.com_id = s2.com_id

注意使用CTE可以避免少量重复

Answer 2

你有什么理由需要加入或加入吗？在上下文中，您要问com_id问题无关紧要。

尝试这样的事情（这个查询没什么特别的，基本上只是将两者合并在一起）

SELECT
  communications.creation_date as message_date, 
  message as message_text, 
  employees.first_name || ' ' || coalesce(employees.middle_name,'') || ' ' || employees.last_name as message_by
  cs.com_id, 
  cs.first_name ||' ' || cs.last_name AS recipient_name, 
  cs.sim_number AS phone_number
FROM app.communications, app.communication_sms cs
INNER JOIN app.employees ON communications.message_from = employees.emp_id 
WHERE send_as_sms = TRUE AND com_id = (SELECT MAX(com_id) FROM app.communications)
AND cs.com_id = (SELECT MAX(cs2.com_id) FROM app.communication_sms cs2)
ORDER BY first_name ASC

Answer 3

第一次查询：您希望MAX(c.com_id)标识的上次通信，但仅限于短信（c.send_as_sms = TRUE）。对于此短信，您需要发件人的姓名。此查询会产生一行或零行，具体取决于上次通信是否为SMS。

第二次查询：您希望此时由MAX(cs.com_id)标识的上次短信通信的最后一条短信。这看起来多余。当您从匹配的send_as_sms记录的存在中看到这是一条短信时，为什么communications中有communication_sms？您可能想要考虑这个设计。无论如何，你想要得到收件人的姓名和一些电话号码。

如何组合这两个查询并不明显。您真的想要收件人姓名的最新短信，但只有最后一次短信也是最后一次通讯时才添加发件人姓名吗？这似乎不太可能。我想你更想要

最新通讯，如果是短信或
最新的短信通讯

发件人和收件人。或者，您是否可以通过短信连接进行非短信通信？

以下是上次短信通信的查询：

SELECT
  c.creation_date AS message_date, 
  c.message AS message_text, 
  e.first_name || ' ' || coalesce(e.middle_name,'') || ' ' || e.last_name AS message_by,
  cs.com_id, 
  cs.first_name ||' ' || cs.last_name AS recipient_name, 
  cs.sim_number AS phone_number
FROM (SELECT * FROM app.communication_sms ORDER BY com_id DESC FETCH FIRST ROW ONLY) cs
JOIN app.communications c ON c.com_id = cs.com_id
JOIN app.employees e ON c.message_from = e.emp_id 
ORDER cs.first_name ASC;

在PostgreSQL中将具有不同数据类型和列数的两个SELECT语句合并为一个输出

3 个答案: