ANSI flashback
I am seeing “traditional” Oracle SQL syntax being replaced by “ANSI”-style far more frequently than I used to – so I thought I’d just flag up another reminder that you shouldn’t be too surprised if you...
View ArticleChar problems
The semantics of comparing character columns of different types can lead to some confusion, so before I get into the main body of this note here’s a little test based on a table with one row: create...
View ArticleJoin Elimination bug
It is possible to take subquery factoring (common table expressions / CTEs) too far. The most important purpose of factoring is to make a complex query easier to understand – especially if you can...
View Articlemaxquerylen
The view v$undostat is a view holding summary information about undo activity that can be used by the automatic undo mechanism to deal with optimising the undo retention time (hence undo space...
View ArticleFake Baselines – 2
Many years ago (2011) I wrote a note describing how you could attach the Outline Information from one query to the SQL_ID of another query using the official Oracle mechanism of calling...
View ArticleSequence Costs
You’re probably aware of the “identity” construct that appeared in 12.1 and uses Oracle’s sequence mechanism to model the Autonumber or Identity columns that other databases have. A posting from Clay...
View ArticleUSING bug
The Oracle Developer Community forum often sees SQL that is hard to read – sometimes because it’s a brutal tangle of subqueries, sometimes because the format it bad, sometimes because the use of table...
View ArticleOrder By
This is a brief note with an odd history – and the history is more significant than the note.While searching my library for an example of an odd costing effect for the “order by” clause I discovered a...
View ArticleCase and Aggregate bug
The following description of a bug appeared on the Oracle Developer Community forum a little while ago – on an upgrade from 12c to 19c a query starting producing the wrong results on a simple call to...
View ArticleFlashback Bug
Here’s a problem with the “flashback versions” technology that showed up at the end of last week. There’s a thread about it on the Oracle Developer community forum, and a chain of tweets that was my...
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