SQL ON clause v WHERE clause (different results)

Question

Please see the DDL below:

CREATE TABLE TestTable(id int, [name] varchar(30))
CREATE TABLE TestTable2(id int, [name] varchar(30))

INSERT INTO TestTable (id,[name]) values (1,'')
INSERT INTO TestTable (id,[name]) values (2,'Martin')

INSERT INTO TestTable2 (id,[name]) values (1,null)
INSERT INTO TestTable2 (id,[name]) values (2,'Martin')

select TestTable.* from TestTable
LEFT JOIN TestTable2 
ON TestTable.id=TestTable2.id 
and TestTable.[name]= TestTable2.[Name] and NOT (TestTable.[name] ='' and TestTable2.[name] is null)
where testtable2.id is null

The SELECT returns one row and I would expect it to return none. The reason I would expect it to return none is the same reason the SQL statement below returns none:

select TestTable.* from TestTable
LEFT JOIN TestTable2 
ON TestTable.id=TestTable2.id 
and TestTable.[name]= TestTable2.[Name] 
where testtable2.id is null and NOT (TestTable.[name] ='' and TestTable2.[name] is null)

Why does the first SQL statement return one row? The ON clause should filer out those records with this criteria: NOT (TestTable.[name] ='' and TestTable2.[name] is null). The one row returned contains this criteria. Why?

Answer 1

A LEFT JOIN will return all rows from the left table unless they are filtered out by the WHERE criteria, your first query WHERE criteria excludes 1 row, the WHERE in your second query excludes both rows.

Update: A popular reference for understanding Joins is:
Visual Representation of SQL Joins

ON is used to define how the tables will be joined together, WHERE to limit the results. In the case of an INNER JOIN they both limit results, with an OUTER JOIN the difference between them becomes appreciable.