Union on two tables based on a specific column - sql-server

Question

I have two tables which have many records , both table have few records where the id is same , I want to have unique group of rows where I have unique id from one particular table incase there are two same id in table
for example
In the above snippet we have empid 1 on both table so , I want all the records such that If there are common empid in both table then value for the common empid the value should be used from Dummy_tab_2 table .
Desired O/P
code to replicate
CREATE TABLE Dummy_tab_1
(
empid int,
Month1 int,
Month2 int,
);
INSERT INTO Dummy_tab_1
VALUES (1, 100, 200), (5,15, 20), (6, 20, 30);
CREATE TABLE Dummy_tab_2
(
empid int,
Month1 int,
Month2 int,
);
INSERT INTO Dummy_tab_2
VALUES (1, 10, 20), (2,15, 20), (3, 20, 30);
I tried this but not sure how to remove the emp id which is not desired
SELECT *
FROM Dummy_tab_2
UNION
SELECT *
FROM Dummy_tab_1
and o/p which I got is this

Answer 1

Using:
SELECT * FROM Dummy_tab_1 WHERE empid NOT IN (SELECT empid FROM Dummy_tab_2)
UNION ALL
SELECT * FROM Dummy_tab_2;
db<>fiddle demo

Answer 2

Using your data examples and what looks like your desired results this should work:
CREATE TABLE Dummy_tab_1
(
empid int,
Month1 int,
Month2 int,
);
INSERT INTO Dummy_tab_1
VALUES (1, 100, 200), (5,15, 20), (6, 20, 30);
CREATE TABLE Dummy_tab_2
(
empid int,
Month1 int,
Month2 int,
);
INSERT INTO Dummy_tab_2
VALUES (1, 10, 20), (2,15, 20), (3, 20, 30);
SELECT COALESCE(DT1.empid, DT2.EmpID) AS EmpID, CASE WHEN DT2.empid IS NOT NULL THEN DT2.Month1 ELSE DT1.Month1 END AS Month1,
CASE WHEN DT2.empid IS NOT NULL THEN DT2.Month2 ELSE DT1.Month2 END AS Month2
FROM Dummy_tab_1 DT1
FULL JOIN Dummy_tab_2 DT2 ON DT1.empid = DT2.empid
ORDER BY COALESCE(DT1.empid, DT2.EmpID)