In SQL, What's the difference a ON condition following a Join vs at the end of multiple JOINS - sql

Question

I have been having a hard time googling an answer for this, but....
can someone explain to me the difference between putting the ON condition of a JOIN with the the JOIN itself vs putting the ON at the end of all the other JOINs.
here is an example http://sqlfiddle.com/#!3/e0a0f/3
CREATE TABLE TableA (Email VARCHAR(100), SomeNameA VARCHAR(100))
CREATE TABLE Tableb (Email VARCHAR(100), SomeNameB VARCHAR(100))
CREATE TABLE Tablec (Email VARCHAR(100), SomeNameC VARCHAR(100))
INSERT INTO TableA SELECT 'joe#test.com', 'JoeA'
INSERT INTO TableA SELECT 'jan#test.com', 'JaneA'
INSERT INTO TableA SELECT 'dave#test.com', 'DaveA'
INSERT INTO TableB SELECT 'joe#test.com', 'JoeB'
INSERT INTO TableB SELECT 'dave#test.com', 'DaveB'
INSERT INTO TableC SELECT 'joe#test.com', 'JoeC'
INSERT INTO TableC SELECT 'dave#test.com', 'DaveC'
SELECT TOP 2 a.*,
b.*,
c.*
FROM TableA a
LEFT OUTER JOIN TableB b
ON a.email = b.email
INNER JOIN TableC c
ON c.Email = b.email;
SELECT TOP 2 a.*,
b.*,
c.*
FROM TableA a
LEFT OUTER JOIN TableB b
INNER JOIN TableC c
ON c.Email = b.email
ON a.email = b.email;
I don't understand why these two SELECT statements produce different results.

Answer 1

What matters is orders of joins. Treat your expressions as if every join produced temporary "virtual" table.
So when you write
FROM TableA a
LEFT OUTER JOIN TableB b ON a.email = b.email
INNER JOIN TableC c ON c.Email = b.email ;
then order is as follows:
TableA is left joined to TableB producing temporary relation V1
V1 is inner joined to TableC.
Meanhwile when you write:
FROM TableA a
LEFT OUTER JOIN TableB b
INNER JOIN TableC c ON c.Email = b.email ON a.email = b.email;
then order is as follows:
TableB is inner joined to TableC producing temporary relation V1.
TableA is left joined to V1.
Thus results are different. It is generally recommended to use parenthesis in such situations to improve readability of the query:
FROM TableA a
LEFT OUTER JOIN
(TableB b INNER JOIN TableC c ON c.Email = b.email)
ON a.email = b.email;

Answer 2

In your second example, the part ON a.email = b.email belongs to the LEFT JOIN.
If written like this, it means the following:
INNER JOIN TableC with TableB and LEFT OUTER JOIN the result with TableA.
The result will be all rows from TableA joined with those rows from TableB that also have an entry in TableC.
The first example means the following:
LEFT OUTER JOIN TableB with TableA and INNER JOIN TableC with the result. This is equivalent to using an INNER JOIN for TableB.
Explanation: When you LEFT OUTER JOIN TableA with TableB you will get all rows from TableA and for matching rows in TableB you will get that data, too. In your result set you will have rows with b.email = NULL and this will now be INNER JOINed with TableC. As long as there is no entry in TableC with email = NULL you will get the results you observed.