CODEWITHSUNDEEP
mysqlsqldatabase
ayushgp
ayushgp

Reputation: 5091

What is the difference between these 2 JOINs?

I have the following 2 SQL SELECT statements and am not able to wrap my head around how they're different: 

SELECT DISTINCT product.maker 
FROM product, pc 
WHERE pc.model = product.model AND 
product.maker NOT IN 
(SELECT DISTINCT product.maker 
   FROM product, laptop 
   WHERE product.model = laptop.model)

and 

SELECT DISTINCT p.maker 
FROM Product p INNER JOIN 
 PC ON p.model = PC.model
WHERE p.maker NOT IN (SELECT ip.maker 
 FROM Laptop il INNER JOIN 
 Product ip ON il.model = ip.model
 );

EDIT: The database schema is here - http://www.sql-ex.ru/help/select13.php#db_1

Upvotes: 0

Views: 55

Answers (1)

Satish Prakash Garg
Satish Prakash Garg

Reputation: 2233

So first obvious difference is absence of DISTINCT in second query's subquery.

The other difference that the second one uses the keyword inner join.

Now, the first way of writing the query is the classical way when join keyword was non-existent.

Using join keyword helps when you have multiple types of join to do such as left join, etc.

Usually the query processor will generate the same database operations, so the performance would be same.

Upvotes: 1

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