Question

我想知道我的哪些用户在他们的机器上有一个独特的操作系统

我对任何不完全独特的人都不感兴趣。（我们在这里寻找孤独的狼）我不是在寻找独特的价值观。只是完全独特的记录。

这是SQL

CREATE  TABLE `Computers` (
  `ID` INT NOT NULL AUTO_INCREMENT ,
  `CPU` VARCHAR(45) NULL ,
  `OS` VARCHAR(45) NULL ,
  PRIMARY KEY (`ID`) );


INSERT INTO `Computers` (`CPU`, `OS`) VALUES ('386', 'win 3.1');
INSERT INTO `Computers` (`CPU`, `OS`) VALUES ('486', 'Dr Doss');
INSERT INTO `Computers` (`CPU`, `OS`) VALUES ('286', 'win 3.1');
INSERT INTO `Computers` (`CPU`, `OS`) VALUES ('68000', 'Mac OS 7.1');
INSERT INTO `Computers` (`CPU`, `OS`) VALUES ('68030', 'Mac OS 7.1');
INSERT INTO `Computers` (`CPU`, `OS`) VALUES ('Z80', 'CPM');

鉴于此数据，我应该只返回以下行：

ID       OS
2        Dr Doss
6        CPM

有人可以帮我解决SQL语句吗？

Answer 1

将GROUP BY子句与HAVING COUNT()一起使用。

SELECT ID, OS
FROM Computers
GROUP BY OS
HAVING COUNT(OS) = 1;

GROUP BY子句将其缩小为每个操作系统一行，HAVING子句筛选出表中有多行的操作系统。

Answer 2

http://sqlfiddle.com/#!2/cbfc2/11

使用上面提供的示例

select min(`id`), `os`, count(*) as total
from computers
group by `os`
having `total` = 1

Answer 3

此？

SELECT * FROM computers
GROUP BY OS
HAVING COUNT(ID) = 1

<强> SQL FIDDLE TEST

Answer 4

SELECT *
FROM computers
INNER JOIN
(
SELECT OS, COUNT(*) AS OsCount
FROM computers
GROUP BY OS
HAVING OsCount = 1
) Sub1
ON computers.OS = Sub1.OS

mySQL中具有唯一（不明显）值的记录

4 个答案: