Does the placement of a condition matter?
I'm not able to quite understand why, but the 2 following queries are giving me different results

    SELECT A.source_code, B.quantity
    FROM Table_A A
    LEFT JOIN Table_B B ON B.merchant_id = A.merchant_id AND B.agent_id = A.agent_id AND B.default IS NULL
    WHERE A.month='2011-10-01' AND B.type='600'

And 

    SELECT A.source_code, B.quantity
    FROM Table_A A
    LEFT JOIN Table_B B ON B.merchant_id = A.merchant_id AND B.agent_id = A.agent_id
    WHERE A.month='2011-10-01' AND B.type='600' AND B.default IS NULL


I had assumed that the condition does the same operation on both queries, only at different times. Am I missing something? Thanks!
Does the placement of a condition matter?
===

I'm not able to quite understand why, but the 2 following queries are giving me different results

    SELECT A.source_code, B.quantity
    FROM Table_A A
    LEFT JOIN Table_B B ON B.merchant_id = A.merchant_id AND B.agent_id = A.agent_id AND B.default IS NULL
    WHERE A.month='2011-10-01' AND B.type='600'

And 

    SELECT A.source_code, B.quantity
    FROM Table_A A
    LEFT JOIN Table_B B ON B.merchant_id = A.merchant_id AND B.agent_id = A.agent_id
    WHERE A.month='2011-10-01' AND B.type='600' AND B.default IS NULL


I had assumed that the condition does the same operation on both queries, only at different times. Am I missing something? Thanks!