sql - 如何在 SQL 中创建 bool 计算字段并加入该计算字段？

Question

首先检查这段代码。我似乎应该对我有用，但事实并非如此! (惊喜!)

无论如何，这是我首先尝试的:

SELECT
Status as status,
Address as ip,
PCName as pc_name,
(Numbers.Phone = 'CPU/' + PCName) as cpu_contact,
(Numbers.Phone = 'PC/' + PCName) as pc_contact,
(Numbers.Phone = 'LOGIN/' + PCName) as login_contact,
FROM IPAddress
WHERE $where  --Generated In code
JOIN Numbers
  ON ('CPU/' + PCName = Numbers.Phone) 
  OR ('PC/' + PCName = Numbers.Phone) 
  OR ('LOGIN/' + PCName = Numbers.Phone)

所以我想要的是一些 bool 计算字段并在类似条件下加入。我还希望结果折叠成单行。例如，我认为当前的设置会做这样的事情:

status ip  cpu_contact pc_contact login_contact
-----------------------------------------------
foo    bar true        false      false
foo    bar false       true       false
foo    bar false       false      true

显然我更愿意

status ip  cpu_contact pc_contact login_contact
-----------------------------------------------
foo    bar true        true       true

有什么想法吗？数据库重新设计不是一种选择。如果是的话，我会那样做:-)

Answer 1

您可以使用 GROUP BY 和 SUM 来折叠行:

SELECT
  Status as status, Address as ip, PCName as pc_name,
  cast(sum(case when (Numbers.Phone = 'CPU/' + PCName) then 1 else 0 end) as bit)
    as cpu_contact,
  cast(sum(case when (Numbers.Phone = 'PC/' + PCName) then 1 else 0 end)) as bit)
    as pc_contact,
  cast(sum(case when (Numbers.Phone = 'LOGIN/' + PCName) then 1 else 0 end) as bit)
    as login_contact,
FROM
  IPAddress
    JOIN Numbers ON 
      ('CPU/' + PCName = Numbers.Phone) OR ('PC/' + PCName = Numbers.Phone) OR 
      ('LOGIN/' + PCName = Numbers.Phone)
WHERE
  $where  --Generated In code
GROUP BY
  Status, Address, PCName

由于您在行之间进行逻辑或运算，因此总和为零为假，而任何大于 0 的值都为真。