How to update SQL Server column after from different table

I have a table called TableA that stored list of event like this

Event_Id     Event_Name
1            Found in AD
2            Found in AAD

I have another table call Table B and it look something like this

Event_Id    UserName      Extra
NULL        David         Found In AAD
1           James         Found in AD
Null        Ronal         Null

I'm just trying to update only a missing/Null value in TableB Event_ID column based on comparing Table1 Event_Name and TableB Extra columns.

I'm doing manually process like this for now so I would be really appreciated If I can get any help on how to join directly between the two table and update it.

Update Table B
  Set Event_Id = case
         when Extra = 'Found in AAD' then 2
 end

Solution

You can use a simple sub-query in your UPDATE to do that.

UPDATE TableB SET
    Event_Id = (SELECT Event_Id from TableA a where a.Event_Name = TableB.Extra)
WHERE Event_Id is null;