Left JOIN and join multiple table joins

Four sheets contract, customer, Customer3, Customer4:

This is a more familiar 3-sheet connection
SELECT *
From Test.contract A
JOIN Test.customer b on a.num = b.num2
JOIN test.customer3 C on a.num = C.NUM3;

The connection is not necessarily followed by a join to the first table.
SELECT *
From Test.contract A
JOIN Test.customer b on a.num = b.num2
Left JOIN test.customer4 D on b.num2 = d.num4;

SELECT *
From Test.contract A
JOIN Test.customer b on a.num = b.num2
Left JOIN test.customer4 D on a.num = d.num4;
This is the same as the result of the previous sentence.
Note that the bold place, I think, is to take A and B's join result set and then the D table left join, at which point a B is still in scope. To avoid confusion, you can set the result of a B as an individual name tmp
SELECT * FROM
(SELECT *
From Test.contract A
JOIN Test.customer b on a.num = B.NUM2) tmp
Left JOIN test.customer4 d on tmp.num = D.NUM4;
Results Ibid.
PS: Multiple table Join table connection order from left to right