Why am I loosing table data from adding additional join statement in SQL Server?

Question

So I have table X with let's say 50 rows of data in it and it is being joined to another table with only 2 rows in it. When I "normal" JOIN them together only the overlapping data will show, i.e. the two rows of data that are found in the larger collection of 50. In my case I want all 50 rows to persist so I use a LEFT JOIN and I am returned all 50 rows like planned.

Now I want to start adding and joining in other tables to get additional data about these rows and have them display togehter, whenever there is no data, I am fine with getting null. Now I'm adding a new JOIN and it's only going to find data for those two rows and not for the other 48, which is perfectly fine and I would like NULL to be displayed where no match is found. My problem is that rather than doing that, displaying null, it is instead removing the 48 rows will partial null data in their columns entirely and only showing the two that match, WHY?

I can provide code if needed, I thought this may be easier to understand.

Answer 1

If you inner join the third table, there are only 2 rows that can match (I assume you don't match on nulls). Only 2 rows from the second table have non-null values in them, so only those 2 can produce a result if you do an inner join with the third table.

You will need another left join in this case. This will return all the rows from the second table, including those that are all null (as the result of the first left join).