如何在TSQL中创建布尔计算字段并加入该计算字段？

Question

首先看看这段代码。 我觉得它应该适合我，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布尔计算字段并在类似条件下加入。 我还希望结果可以折叠成单行。 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

显然我宁愿

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

有任何想法吗？ 数据库重新设计不是一种选择。 如果是的话，我会这样做:-)

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

由于您正在执行逻辑或行之间，因此零之和为false，而大于0的任何值都为true。

Answer 2

您需要使用Case / When进行比较。 在这种情况下，我硬编码1或0，但T-SQL会将硬编码的数字转换为int。 如果你想要布尔（位），你需要手动转换，就像这样......

Convert(Bit, Case When Numbers.Phone = 'CPU/' + PCName Then 1 Else 0 End) as cpu_contact,
Convert(Bit, Case When Numbers.Phone = 'PC/' + PCName Then 1 Else 0 End) as pc_contact,
Convert(Bit, Case When Numbers.Phone = 'LOGIN/' + PCName Then 1 Else 0 End) as login_contact,

Answer 3

SELECT
Status as status,
Address as ip,
PCName as pc_name,
case when sum(case when Numbers.Phone = 'CPU/' + PCName then 1 end) > 0 then 'true' else 'false' end as cpu_contact,
case when sum(case when Numbers.Phone = 'PC/' + PCName then 1 end) > 0 then 'true' else 'false' end as pc_contact,
case when sum(case when Numbers.Phone = 'LOGIN/' + PCName then 1 end) > 0 then 'true' else 'false' end as login_contact
FROM IPAddress
JOIN Numbers
  ON ('CPU/' + PCName = Numbers.Phone) 
  OR ('PC/' + PCName = Numbers.Phone) 
  OR ('LOGIN/' + PCName = Numbers.Phone)
WHERE -- your condition goes here
group by status, address, pc_name