sel a.t1,b.t1 from emp a left outer join dept b ON
a.id=b.id where b.deptno=10;
sel a.t1,b.t1 from emp a left outer join dept b ON
a.id=b.id and b.deptno=10;
what is the difference on the above 2 queries?
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Answer Posted / tdguy
This is a good question. If we look at the explain plans,we
would be able to understand the difference.
1. In the first query, the condition given in where clause
is applied after the left outer join process on the tables.
This means that it is a plain left outer jon on id column
between the tables and the where condition is applied after
the join process. This can be seen in the explain plan as
"by way of a RowHash match scan with a condition".
2. In the second query, the condition given in and
statement clause is applied along with the left outer join
process on the tables. This means that it is a left outer
jon on id column between the tables with table b with only
one row. This can be seen in the explain plan as
"by way of a RowHash match scan with no residual conditions
".
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