Last week one of my friend ask me,
"Why database return different result set when we upgrade from Oracle9i to Oracle 11g?"
He mean to say that, sql statement which return correct result in Oracle 9i, is not returning same result set in Oracle 11g.
I immediately told him to check data, May be data are not properly migrated. But I was wrong as he already validate that. Then I ask for table structure and sql statement. After analysis of sql statement I come to the conclusion that new Oracle 11g(and even 10g) optimizer may ignore left outer join and instead perform Inner join.
This is possible when you have not written sql join properly or sometime because of ANSI sql.
I will post detailed scenario and explanation later on this week.
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