WHERE vs JOIN which is the best

Question

dear all
I learned to make join between emp table and dept table using the where clause.
Example :
select e.ename,d.dname
from emp e, dept d
where e.deptno = d.deptno;
One of my friends told me that join using where clause is not good in performance, instead one has to use join clause
example
select e.ename,d,dname
from emp e join dept d on (e.deptno = d.deptno);
I just want to know which one is best in performance ?
Please I need your advice

Answer 1

If you want to find a difference, using WHERE is the traditional, classical Oracle syntax. Uning JOIN is ANSI SQL99 syntax, introduced in Oracle RDBMS 9iRel1.
Now let's play MythBusters. The optimizer will interpret both syntaxes (Traditional, and ANSI SQL99) exactly the same. If you use the classical AUTOTRACE you will realize both syntaxes produce the same execution plan and both of them will use the same amount of resources, as shown below.
SQL> set autotrace traceonly
SQL> select e.ename,d.dname
2 from emp e, dept d
3 where e.deptno = d.deptno;
14 rows selected.
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 MERGE JOIN
2 1 SORT (JOIN)
3 2 TABLE ACCESS (FULL) OF 'DEPT'
4 1 SORT (JOIN)
5 4 TABLE ACCESS (FULL) OF 'EMP'
Statistics
0 recursive calls
0 db block gets
36 consistent gets
0 physical reads
0 redo size
655 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
14 rows processed
SQL> select e.ename,d.dname
2 from emp e join dept d on (e.deptno = d.deptno);
14 rows selected.
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 MERGE JOIN
2 1 SORT (JOIN)
3 2 TABLE ACCESS (FULL) OF 'DEPT'
4 1 SORT (JOIN)
5 4 TABLE ACCESS (FULL) OF 'EMP'
Statistics
0 recursive calls
0 db block gets
36 consistent gets
0 physical reads
0 redo size
655 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
14 rows processed
Conclusion, if you want to improve performance consider using indexes, generate statistics on your segments, use an analytical approach. There are so many other ways to improve performance.