Update table if exist or insert if not - sql

Question

I have 2 SQL tables with same column label, Table1 and Table2.
I want to update Table1 with value of Table2 if there is a same value for an attribute.
The tables has CODE, POSITION, DESCRIPTION as columns.
I do this:
UPDATE Table1
SET CODE = Table2.CODE,
POSITION= Table2.POSITION
FROM Table2
WHERE DESCRIPTION = Table2.DESCRIPTION
It works, but if in the DESCRIPTION Value of Table2 is not present into Table1, I want to insert the entire row, in other words I need to do something like:
UPDATE IF DESCRIPTION EXISTS
ELSE INSERT
How can I do this?

Answer 1

You can do this from first-principals in 2 steps
Update the existing values like you have done:
UPDATE Table1
SET
CODE= t2.CODE,
POSITION= t2.POSITION
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.DESCRITPION = t2.DESCRITPION
Then you can insert the missing records
INSERT INTO Table1 (CODE, POSITION, DESCRITPION)
SELECT CODE, POSITION, DESCRITPION
FROM Table2 t2
WHERE NOT EXISTS (SELECT DESCRITPION
FROM Table1 t1
WHERE t1.DESCRITPION = t2.DESCRITPION)
Most RDBMS have a MERGE statement that allows you to combine these two queries into a single atomic operation, you'll need to check the documentation for your vendor, but an MS SQL Server MERGE solution looks like this:
MERGE INTO Table1 AS tgt
USING Table2 AS src
ON tgt.DESCRITPION = src.DESCRITPION
WHEN MATCHED
THEN UPDATE SET CODE= src.CODE,
POSITION= src.POSITION
WHEN NOT MATCHED THEN
INSERT (CODE, POSITION, DESCRITPION)
VALUES (src.CODE, src.POSITION, src.DESCRITPION)
An additional benefit to the MERGE clause is that it simplifies capturing the changed state into the OUTPUT clause which allows for some complex logic all while keeping the query as a single operation without having to manually create and track transaction scopes.