I set up a demo how this could be done in KNIME although you could do that in consecutive steps or directly in a SQL database (as has been mentioned) but it is possible. Here I use SQLite which I like because it is a ‘real’ SQL database but you can just have it within one single file (you could switch that out for any SQL database).
The Join itself is done in the SQL Executor node. Plus: you have it in one step. The downside could be it might get a little bit confusing with all the steps, but you have it in one step (sort of 
).
DROP TABLE IF EXISTS data2;
CREATE TABLE data2 AS
SELECT *
FROM data1 d1
LEFT JOIN dimension1 t1
ON d1.ID1 = t1.ID2
LEFT JOIN dimension2 t2
ON d1.ID1 = t2.ID3
kn_example_sqlite_multiple_joins.knwf (63.8 KB)