Cost Based Optimizer

12c SQL Plan Directive: state has changed between 12.1.0.1 and 12.1.0.2

By Franck Pachot . SQL plan Directives have been introduced in 12c. If you have scripts that check their states (and I have that as I prefer to monitor closely the features that are new) you probably have seen(…)

Oracle 12.1.0.2.1 Set to Join Conversion

By Franck Pachot . Recently, I described the Partial Join Evaluation transformation that appeared last year in Oracle 12c. I did it as an introduction for another transformation that appeared long time ago in 10.1.0.3 but was not(…)

Partial Join Evaluation in Oracle 12c

By Franck Pachot . Do you think that it’s better to write semi-join SQL statements with IN(), EXISTS(), or to do a JOIN? Usually, the optimizer will evaluate the cost and do the transformation for you. And in this(…)

ROWNUM vs ROW_NUMBER() and 12c fetch first

By Franck Pachot . Prior to Oracle 12c, there were two ways to do ‘top-n’ queries: use rownum after sorting rows with “order by” use row_number() over (order by) Top-n queries are usually required for result pagination. The application(…)