Updating the first occurrence of the column with a value and the remaining with other value - sql

Question

select emp_id, emp_dept, emp_name
from employee
where emp_id in (123, 234);
emp_id emp_dept emp_name
*****************************
123 222 1234
123 222 5678
123 222 9101
234 222 1011
234 222 1112
234 222 1213
Here there are 3 records for each emp_id.
I want a query to update the emp_dept such that out of three records, only one record will be updated to 555(it can be any record doesnt matter) and the other 2 will be updated to 666.

Answer 1

Create a CTE (common table expression) adding a ROW_NUMBER window function partitioned by emp_id then write an update statement joining the cte and building a case statement to determine row number
The code below builds a Table Variable with Test data, selects the data to show you the "before" and then modifies with the cte method and selects the data to show you the final result.
;WITH cte AS (
SELECT
emp_id
,ROW_NUMBER() OVER (PARTITION BY emp_id ORDER BY emp_SSN) AS RowNum
FROM
#Table
)
UPDATE t
SET emp_dept = CASE WHEN RowNum = 1 THEN 555 ELSE 666 END
FROM
#Table t
INNER JOIN cte u
ON t.emp_id = u.emp_id

Answer 2

You can use MERGE.
Data Preparation
create table em1(
emp_id number, emp_dept number, emp_name varchar2(10));
insert into em1 values(123,1,'we');
insert into em1 values(123,1,'asd');
insert into em1 values(123,1,'rfw');
insert into em1 values(345,2,'rtg');
insert into em1 values(345,2,'bfg');
insert into em1 values(345,2,'uyi');
commit;
Query
MERGE INTO em1 e
USING (
SELECT emp_id, emp_dept, emp_name,
row_number() over (partition by emp_id order by 1) r
FROM em1
WHERE emp_id in (123,345)
) f
ON (f.emp_id = e.emp_id and f.emp_name = e.emp_name)
WHEN MATCHED THEN
UPDATE SET e.emp_dept = case when f.r = 1 then 555 else 666 end;
Result
emp_id emp_dept emp_name
-------------------------
123 555 we
123 666 asd
123 666 rfw
345 555 rtg
345 666 bfg
345 666 uyi