I was wondering performance wise what would be faster a join or a from and where query. I am trying merge and update query but performance is terrible?
If you are asking whether it is more efficient to use SQL 92 join syntax
SELECT empno, ename, dname FROM emp JOIN dept USING (deptno)
or to use the older join syntax
SELECT empno, ename, dname FROM emp e, dept d WHERE e.deptno = d.deptno
the answer is that it doesn't matter. The optimizer is automatically going to do an internal transformation from the SQL 92 syntax to the older syntax anyway.
If you have performance problems, it is highly unlikely that they are related to your choice of join syntax (though when Oracle first added support for SQL 92 join syntax, there were bugs relating to its ability to transform the SQL into the older style).