Inner join vs Where

Question

Is there a difference in performance (in oracle) between

Select * from Table1 T1 
Inner Join Table2 T2 On T1.ID = T2.ID

And

Select * from Table1 T1, Table2 T2 
Where T1.ID = T2.ID

?

Answer 1

If the query optimizer is doing its job right, there should be no difference between those queries. They are just two ways to specify the same desired result.

Answer 2

In PostgreSQL, there's definitely no difference - they both equate to the same query plan. I'm 99% sure that's also the case for Oracle.

Answer 3

They should be exactly the same. However, as a coding practice, I would rather see the Join. It clearly articulates your intent,

Answer 4

They're both inner joins that do the same thing, one simply uses the newer ANSI syntax.

Answer 5

Functionally they are the same as has been said. I agree though that doing the join is better for describing exactly what you want to do. Plenty of times I've thought I knew how I wanted to query something until I started doing the joins and realized I wanted to do a different query than the original one in my head.

Answer 6

They're logically identical but in the earlier versions of Oracle that adopted ANSI syntax there were often bugs with it in more complex cases, so you'll sometimesencounter resistance to using it from Oracle people.

Answer 7

I don't know about Oracle but I know that the old syntax is being deprecated in SQL Server and will disappear eventually. Before I used that old syntax in a new query I would check what Oracle plans to do with it.

I prefer the newer syntax rather than the mixing of the join criteria with other needed where conditions. In the newer syntax it is much clearer what creates the join and what other conditions are being applied. Not really a big problem in a short query like this, but it gets much more confusing when you have a more complex query. Since people learn on the basic queries, I would tend to prefer people learn to use the join syntax before they need it in a complex query.

And again I don't know Oracle specifically, but I know the SQL Server version of the old style left join is flawed even in SQL Server 2000 and gives inconsistent results (sometimes a left join sometimes a cross join), so it should never be used. Hopefully Oracle doesn't suffer the same issue, but certainly left and right joins can be mcuh harder to properly express in the old syntax.

Plus it has been my experience (and of course this is strictly a personal opinion, you may have differnt experience) that developers who use the ANSII standard joins tend to have a better understanding of what a join is and what it means in terms of getting data out of the database. I belive that is becasue most of the people with good database understanding tend to write more complex queries and those seem to me to be far easier to maintain using the ANSII Standard than the old style.

Answer 8

Using JOIN makes the code easier to read, since it's self-explanatory.

In speed, there's no difference (I have just tested it), and the execution plan is the same....

Answer 9

It is true that, functionally, both queries should be processed the same way. However, experience has shown that if you are selecting from views that use the new join syntax, it is important to structure your queries using it as well. Oracle's optimizer can get confused if a view uses a "join" statement, but a query accessing the view uses the traditional method of joining in the "where" clause.

Answer 10

The performance should be identical, but I would suggest using the join-version due to improved clarity when it comes to outer joins.

Also unintentional cartesian products can be avoided using the join-version.

A third effect is an easier to read SQL with a simpler WHERE-condition.

Answer 11

No! The same execution plan, look at these two tables:

CREATE TABLE table1 (
  id INT,
  name VARCHAR(20)
);

CREATE TABLE table2 (
  id INT,
  name VARCHAR(20)
);

The execution plan for the query using the inner join:

-- with inner join

EXPLAIN PLAN FOR
SELECT * FROM table1 t1
INNER JOIN table2 t2 ON t1.id = t2.id;

SELECT *
FROM TABLE (DBMS_XPLAN.DISPLAY);

-- 0 select statement
-- 1 hash join (access("T1"."ID"="T2"."ID"))
-- 2 table access full table1
-- 3 table access full table2

And the execution plan for the query using a WHERE clause.

-- with where clause

EXPLAIN PLAN FOR
SELECT * FROM table1 t1, table2 t2
WHERE t1.id = t2.id;

SELECT *
FROM TABLE (DBMS_XPLAN.DISPLAY);

-- 0 select statement
-- 1 hash join (access("T1"."ID"="T2"."ID"))
-- 2 table access full table1
-- 3 table access full table2

Answer 12

[For a bonus point...]

Using the JOIN syntax allows you to more easily comment out the join as its all included on one line. This can be useful if you are debugging a complex query

As everyone else says, they are functionally the same, however the JOIN is more clear of a statement of intent. It therefore may help the query optimiser either in current oracle versions in certain cases (I have no idea if it does), it may help the query optimiser in future versions of Oracle (no-one has any idea), or it may help if you change database supplier.

Answer 13

Can any one Tell me How to see the Above Execute Query Plan, Do i Need to use any tool ? I am presently I am working on Mysql Database and using SQLYog