Need help to compare pricing using SQL queries
Disclaimer, everything is nullable in your tables so IS NULL predicates may give false positives.

Your query comes a long way, all you need is to add certain predicates:

1 and 2.

SELECT Table1.Brand ,
       Table1.Origin,  
       Table1.Destination,  
       Table1.Price,  
       Table2.Price,
       Table1.Price - Table2.Price as diff 
FROM Table1  
  LEFT JOIN Table2  
         ON Table1.Brand = Table2.Brand  
        AND Table1.Origin = Table2.Origin  
        AND Table1.Destination = Table2.Destination
WHERE Table1.Price - Table2.Price &lt;&gt; 0;   


3 . 

SELECT Table1.Brand ,
       Table1.Origin,  
       Table1.Destination,  
       Table1.Price,  
       Table2.Price,
       Table1.Price - Table2.Price as diff 
FROM Table1  
  LEFT JOIN Table2  
         ON Table1.Brand = Table2.Brand  
        AND Table1.Origin = Table2.Origin  
        AND Table1.Destination = Table2.Destination
WHERE Table2.Price IS NULL;