What is semi-join in database?

Question

I am having trouble while trying to understand the concept of semi-join and how it is different from conventional join. I have tried some article already but not satisfied w

Answer 1

As I understand, a semi join is a left join or right join:

What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN?

So the difference between a left (semi) join and a "conventional" join is that you only retrieve the data of the left table (where you have a match on your join condition). Whereas with a full (outer) join (I think thats what you mean by conventional join), you retrieve the data of both tables where your condition matches.