Single AND condition gives the same output as WHERE condition

Question

I tried to compose a query on data.stackexchange.com which would give me the answer to the question what the percentage of users who have written posts which were viewed over 1000 times and who possess badges of a certain class.

Problem: if I write AND ViewCount > 1000 I get the same result as WHERE ViewCount > 1000 I don't understand why it happens

The query with WHERE:

SELECT 
TOP 1000 
Class, (Count(Badges.UserId)* 100 / (SELECT COUNT(*) From Badges)) AS Percentage 
FROM Badges 
WHERE Badges.UserId IN (SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN 
Badges ON Posts.OwnerUserId = Badges.UserId 
WHERE ViewCount > 1000) 
GROUP BY Class 
ORDER BY Class

The query with AND:

SELECT 
TOP 1000 
Class, (Count(Badges.UserId)* 100 / (SELECT COUNT(*) From Badges)) AS Percentage 
FROM Badges 
WHERE Badges.UserId IN (SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN 
Badges ON Posts.OwnerUserId = Badges.UserId 
AND ViewCount > 1000) 
GROUP BY Class 
ORDER BY Class

Output (for some reason it is the same in both cases):

1 class - 2 percent

2 class - 15 percent

3 class - 45 percent

Answer 1

You are using the AND to connect the two expressions in the ON condition of the JOIN. Focus on the inner query:

SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN Badges ON Posts.OwnerUserId = Badges.UserId 
WHERE ViewCount > 1000

Versus:

SELECT Posts.OwnerUserId FROM Posts 
INNER JOIN Badges
ON (
    Posts.OwnerUserId = Badges.UserId 
    AND ViewCount > 1000
)

These two queries are logically equivalent.