删除空值较小的重复项

Question

我有一张员工表,其中包含大约25列.现在有很多重复,我想尝试摆脱一些重复.

首先,我想通过查找在名字,姓氏,员工编号,公司编号和状态中具有相同值的多个记录来查找重复项.

SELECT
    firstname,lastname,employeenumber, companynumber, statusflag
FROM
    employeemaster
GROUP BY
    firstname,lastname,employeenumber,companynumber, statusflag
HAVING 
    (COUNT(*) > 1)

这给了我重复但我的目标是找到并保持最好的单个记录并删除其他记录."最佳单条记录"由所有其他列中具有最少NULL值的记录定义.我怎样才能做到这一点？

我正在使用Microsoft SQL Server 2012 MGMT Studio.

例:

红色:删除绿色:保持

注意:表中的列数多于此表所示的列数.

Answer 1

您可以使用 sys.columns 表获取列列表并构建动态查询。此查询将根据给定条件为您想要保留的每条记录返回“KeepThese”值。

-- insert test data
create table EmployeeMaster
  (
    Record int identity(1,1),
    FirstName varchar(50),
    LastName varchar(50),
    EmployeeNumber int,
    CompanyNumber int,
    StatusFlag int,
    UserName varchar(50),
    Branch varchar(50)
  );
insert into EmployeeMaster
  (
    FirstName,
    LastName,
    EmployeeNumber,
    CompanyNumber,
    StatusFlag,
    UserName,
    Branch
  )
  values
    ('Jake','Jones',1234,1,1,'JJONES','PHX'),
    ('Jake','Jones',1234,1,1,NULL,'PHX'),
    ('Jake','Jones',1234,1,1,NULL,NULL),
    ('Jane','Jones',5678,1,1,'JJONES2',NULL);

-- get records with most non-null values with dynamic sys.column query
declare @sql varchar(max)
select @sql = '
    select e.*,
        row_number() over(partition by
                            e.FirstName,
                            e.LastName,
                            e.EmployeeNumber,
                            e.CompanyNumber,
                            e.StatusFlag
                          order by n.NonNullCnt desc) as KeepThese
    from EmployeeMaster e
        cross apply (select count(n.value) as NonNullCnt from (select ' +
            replace((
                select 'cast(' + c.name + ' as varchar(50)) as value union all select '
                from sys.columns c
                where c.object_id = t.object_id
                for xml path('')
                ) + '#',' union all select #','') + ')n)n'
from sys.tables t
where t.name = 'EmployeeMaster'

exec(@sql)