是否存在使用SQL Server 2016的SQL查询以仅显示没有重复的记录？

Question

I have

How to query so that the results will only display record having no duplicate without hard coding? See results

Answer 1

If you want empcode s with no duplicates, then one simple way uses aggregation:

select empcode, min(leavecode) as leavecode
from t
group by empcode
having count(*) = 1;

This works, because if there is only one row for an empcode , then min(leavecode) is the leavecode .

An alternative method uses window functions:

select empcode, leavecode
from (select t.*, count(*) over (partition by empcode) as cnt
      from t
     ) t
where cnt = 1;

Or, if leavecode s are unique when there are duplicates, perhaps the most efficient way:

select t.*
from t
where not exists (select 1
                  from t t2
                  where t2.emp_code = t.empcode and t2.leavecode <> t.leavecode
                 );

Answer 2

You just select those records that have the empcode in a table of empcodes that only have one occurrence.

SELECT
  empcode,
  leavecode
FROM mytable
WHERE empcode in (
  SELECT empcode FROM mytable GROUP BY empcode HAVING count(1)=1
)