清理数据库记录

Question

我有一个没有真正规范化的数据库，所以我回过头来尝试使其更好一些。 现在，我们有以下几列：

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 

我如何找到拥有2名相同姓名，学年，年级和学校ID的人的学校？ 它们看起来像数据库中的重复项（所有列都相同），但是每个玩家每年只有一排游戏。 这就是我所知道的，在学校中有相似的人，会有两行具有相同的信息。

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

如果我正确理解了您的问题，则此查询：

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

这基本上将找到存在多个记录中的所有（名字，姓氏，学年，成绩，学号）集。

如果您仅对上述记录的SchoolId感兴趣，请继续：

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

Answer 3

一个简单的GROUP BY和HAVING应该可以：

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

请注意，如果要查找所有重复学生的学校，则可能需要使用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