为 SQL 查询创建一个 if 语句

Question

我想要一个类似于以下相同示例的视图，其中数据是从 3 个不同的表中提取的

我想创建一个查询，它将 select 每个 company 及其 location、rooms 和 adddress，但是如果 company 在 CA 中有一个位置我不想 select 在 NY 或 OR 中的任何其他位置。我看到 CASE 但我不确定在这种情况下如何使用它，因为我不想输入名称。现在我的查询是这样的

 SELECT DISTINCT TOP (100) PERCENT
     DBO.HOTEL.COMPANY, DBO.HOTEL.LOCATION AS LOCATION, DBO.AMOUNT.ROOMS, 
     DBO.PERSON.OWNERS, DBO.PERSON.ADDRESS
 FROM DBO.HOTEL INNER JOIN DBO.HOTEL.ID = DBO.AMOUNT.HOTEL_ID INNER JOIN
      DBO.HOTEL.ID = DBO.PERSON.HOTEL_ID
 WHERE (LOCATION = 'OR' OR LOCATION = 'CA' OR LOCATION = 'NY') AND
       DBO.HOTEL.OPEN_DATE >= 01/01/2015

Answer 1

您可以在此上下文中使用 NOT EXISTS：

SELECT DISTINCT TOP (100) PERCENT
  DBO.HOTEL.COMPANY,
  DBO.HOTEL.LOCATION AS LOCATION,
  DBO.AMOUNT.ROOMS, 
  DBO.PERSON.OWNERS,
  DBO.PERSON.ADDRESS
FROM
  DBO.HOTEL INNER JOIN DBO.HOTEL.ID = DBO.AMOUNT.HOTEL_ID
  INNER JOIN DBO.HOTEL.ID = DBO.PERSON.HOTEL_ID
WHERE
  LOCATION = 'CA' OR (
    (LOCATION = 'OR' OR LOCATION = 'NY')
    AND 
    NOT EXISTS (
        SELECT * FROM DBO.HOTEL h
        WHERE h.id=DBO.HOTEL.ID AND LOCATION='CA'
      )
    )
  AND DBO.HOTEL.OPEN_DATE >= '01/01/2015'

Answer 2

根据你的问题我了解到你想要select每个公司的位置、房间和地址。如果一家公司在加州，您只需要将其列出即可。

你可以尝试这样的事情（这里的例子 http://sqlfiddle.com/#!3/f9897/1）：

create table hotel (
    company char(2),
    location char(2),
    rooms int,
    owners char(3),
    address varchar(20)
);

insert into hotel values 
('C1', 'NY', 32, 'BAP', '123 Appl'),
('C1', 'CA', 21, 'BAP', '123 Appl'),
('C1', 'OR', 24, 'BAP', '123 Appl'),
('C2', 'OR', 54, 'RED', '123 Appl'),
('C3', 'CA', 35, 'EDR', '123 Appl'),
('C4', 'NY', 14, 'LPD', '123 Appl'),
('C5', 'NY', 48, 'LPD', '123 Appl'),
('C6', 'CA', 98, 'WES', '123 Appl'),
('C6', 'OR', 56, 'WES', '123 Appl'),
('C7', 'OR', 61, 'YTR', '123 Appl'),
('C8', 'OR', 12, 'YTR', '123 Appl'),
('C9', 'CA', 25, 'MAD', '123 Appl'),
('C9', 'NY', 65, 'MAD', '123 Appl'),
('C9', 'OR', 38, 'MAD', '123 Appl');

select * from hotel
where location = 'CA'
    union all
select * from hotel
where company not in (select company from hotel where location = 'CA');

Result
company location    rooms   owners  address
C1      CA          21      BAP     123 Appl
C2      OR          54      RED     123 Appl
C3      CA          35      EDR     123 Appl
C4      NY          14      LPD     123 Appl
C5      NY          48      LPD     123 Appl
C6      CA          98      WES     123 Appl
C7      OR          61      YTR     123 Appl
C8      OR          12      YTR     123 Appl
C9      CA          25      MAD     123 Appl

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