Question

我有一个没有真正规范化的数据库，所以我要回去试图让它变得更好一些。现在我们有以下专栏：

FirstName | LastName | SchoolYear | Grade | SchoolId | Games Played
 Bob      | Smith    | 2010       |  Fr   | 245      | 3
 Tina     | Johnson  | 2010       |  So   | 2894     | 10
 Bob      | Smith    | 2010       |  Fr   | 245      | 3

我如何找到有2名同名，学年，年级和学校ID的学校？它们看起来像数据库中的重复项（所有列都是相同的），但每个玩家只有一行有每年玩的游戏。这就是我知道学校里有类似的人，会有2行有相同的信息。

我正在使用SQL Server 2008

谢谢！

Answer 1

select FirstName, LastName, SchoolYear, Grade, SchoolId
from Student
group by FirstName, LastName, SchoolYear, Grade, SchoolId
having count(*) > 1

Answer 2

如果我理解你的问题，请查询：

SELECT FirstName, LastName, SchoolYear, Grade, SchoolId
FROM <your table>
GROUP BY FirstName, LastName, SchoolYear, Grade, SchoolId
HAVING COUNT(*) > 1

这将基本上找到存在于多个记录中的所有（FirstName，LastName，SchoolYear，Grade，SchoolId）集。

如果您只对以上记录的SchoolId感兴趣，请选择：

SELECT DISTINCT SchoolId
FROM <your table>
GROUP BY FirstName, LastName, SchoolYear, Grade, SchoolId
HAVING COUNT(*) > 1

Answer 3

简单的GROUP BY和HAVING应该：

SELECT SchoolId
FROM YourTable
GROUP BY FirstName, LastName, SchoolYear, Grade, SchoolId, [Games Played]
HAVING COUNT(*) = 2

请注意，如果您想找到所有学生重复的学校，您可能需要使用HAVING COUNT(*) > 1。

Answer 4

SELECT FirstName,
       LastName,
       SchoolYear,
       Grade,
       SchoolId,
       (CASE WHEN COUNT(*) > 1 THEN 'Yes' ELSE 'No' END) AS 'Repeat?'
FROM <table_name>
GROUP BY FirstName, LastName, SchoolYear, Grade, SchoolId

Answer 5

select count(*), FirstName, LastName, SchoolYear, Grade, SchoolId
from mytable
group by FirstName, LastName, SchoolYear, Grade, SchoolId
order by 1 desc

清理数据库记录

5 个答案: