postgresql-检查使用case和exists的表之间是否存在关系

这是我的打包桌

它通过object_tags表连接到tags表，object_id是package.id

如果包装上有特殊标签，或者从今天起购买日期超过3天或更长时间，则包装可被视为特殊包装。这就是输出应该是什么：

+------------+--------------+--------+
| package_id | order_number | is_vip |
+------------+--------------+--------+
|          1 | P1           |      0 |
|          2 | P2           |     -1 |
|          3 | P3           |     -1 |
|          4 | P4           |     -1 |
|          5 | P5           |      0 |
+------------+--------------+--------+

这就是我尝试过的：

  SELECT packages.id as package_id,
    packages.order_number as order_number,
    (CASE
      WHEN EXISTS(SELECT p.id as id
                  FROM packages p
                  INNER JOIN object_tags ot on ot.object_id = p.id
                  INNER JOIN tags t on t.id = ot.tag_id
                  WHERE tag.name = 'special'
                  )vip on packages.id = vip.id THEN -1 /*(PG::SyntaxError: ERROR:  syntax error at or near "vip"*/
      WHEN p.purchased_at NOT BETWEEN NOW() AND NOW() - interval '3 days' then -1
      ELSE 0 END) as is_vip
  FROM packages p

---

我不太确定这件事——这是其中的一部分。任何帮助都将不胜感激

在修复了一些语法错误后，这种方法会起作用，但我认为exists子句不是实现这一点的最干净的方法。像这样的怎么样

select P.id package_id
     , P.order_number
     , (P.purchase_date < (now() - interval '3 days') or T.name = 'special') is_vip
  from packages P
  left join object_tags OT
    on P.id = OT.object_id
  left join tags T
    on OT.tag_id = T.id
   and T.name = 'special'

如果需要将true映射为0，可以将其包装在子查询中。

使用特殊的\u包 像 选择package.id 从包、对象、标签、标签 其中package.id=object\u tags.object\u id AND tags.id=object\u tags.tag\u id AND tags.name='special' 选择package.id作为package\u id， 包装订单号， 案例 当package.purchase\u日期<现在-间隔“3天”然后-1 当special_packages.id不为空时，则为-1 其他0 一如继往 从包装 使用id左键连接特殊_包 这是一个例子。如果您的数据库不支持CTE，则可以将特殊_包移动到子查询中：

选择 从包装 左连接。。。作为使用id的特殊_包

---

在p.id的末尾有一个逗号作为id，它不应该在那里……使用0和-1作为Is_vip列的值有什么特殊原因吗？如果不是，布尔值更有意义。@Nick yep。将更新问题。thanks@SimonLepkin是的，稍后我会处理它们。packages.id=vip.id在查询中没有位置。不知道你想用它实现什么？谢谢！我没想过要加入左撇子！：

  SELECT packages.id as package_id,
    packages.order_number as order_number,
    (CASE
      WHEN EXISTS(SELECT p.id as id
                  FROM packages p
                  INNER JOIN object_tags ot on ot.object_id = p.id
                  INNER JOIN tags t on t.id = ot.tag_id
                  WHERE tag.name = 'special'
                  )vip on packages.id = vip.id THEN -1 /*(PG::SyntaxError: ERROR:  syntax error at or near "vip"*/
      WHEN p.purchased_at NOT BETWEEN NOW() AND NOW() - interval '3 days' then -1
      ELSE 0 END) as is_vip
  FROM packages p

select P.id package_id
     , P.order_number
     , (P.purchase_date < (now() - interval '3 days') or T.name = 'special') is_vip
  from packages P
  left join object_tags OT
    on P.id = OT.object_id
  left join tags T
    on OT.tag_id = T.id
   and T.name = 'special'

SELECT package.id AS package_id, package.order_number AS order_number,
  CASE
     WHEN 'special' = (SELECT tags.name FROM tags WHERE tags.id = object_tags.tag_id) 
          THEN -1
     WHEN package.purchase_date < NOW() - interval '3 days' 
          THEN -1
     ELSE 0
   END AS is_vip
FROM package
LEFT JOIN object_tags ON package.id = object_tags.object_id
ORDER BY packages.id