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CONNECT BY oddity
This week I’ve seen an issue with a CONNECT BY query: for some reason Oracle 10.2.0.4 decided to build a weird plan (the query is weird too, but that’s not my point here ). An explanation of why that...
View ArticleTest Data
The UKOUG conference is over for another year – but it has left me with plenty to do and lots of things to investigate. Here’s just one little point that I picked up during one of the 10 minute “Oak...
View ArticleSubquery Factoring
It’s always worth browsing through the list of Oracle’s bug fixes each time a new release or patch comes out because it can give you clues about where to look for problems in your production release –...
View ArticleSubquery Factoring
Here’s an interesting little conundrum about subquery factoring that hasn’t changed in the recent (11.2.0.3) patch for subquery factoring. It came to me from Jared Still (a fellow member of Oak Table...
View ArticleSubquery Factoring
I have a small collection of postings where I’ve described anomalies or limitations in subquery factoring (the “with subquery”, or Common Table Expression (CTE) to give it the official ANSI name)....
View ArticleReport Generators And Query Transformations
Usually the Cost-Based Optimizer arrives at a reasonable execution plan if it gets the estimates regarding cardinality and data scattering / clustering right (if you want to learn more about that why...
View Article12c subquery factoring
I’ve written a few notes about anomalies in subquery factoring (with subquery) in the past, principally making a fuss about the fact that moving an inline view into a “with subquery” can cause a plan...
View Article12c Subquery Factoring
From time to time I’ve posted a reminder that subquery factoring (“with subquery”) can give you changes in execution plans even if the subquery that you’ve taken out of line is written back inline by...
View ArticleRecursive subquery factoring
This is possibly my longest title to date – I try to keep them short enough to fit the right hand column of the blog without wrapping – but I couldn’t think of a good way to shorten it (Personally I...
View ArticleFunctions & Subqueries
I think the “mini-series” is a really nice blogging concept – it can pull together a number of short articles to offer a much better learning experience for the reader than they could get from the...
View ArticleSubquery Factoring (9)
Several years go (eight to be precise) I wrote a note suggesting that Oracle will not materialize a factored subquery unless it is used at least twice in the main query. I based this conclusion on a...
View ArticleSubquery Factoring (10)
What prompted me to write my previous note about subquerying was an upgrade to 12c, and a check that a few critical queries would not do something nasty on the upgrade. As ever it’s always interesting...
View ArticleExistence
A recent question on the OTN Database Forum asked:I need to check if at least one record present in table before processing rest of the statements in my PL/SQL procedure. Is there an efficient way to...
View ArticleCTEs and Updates
An important target of trouble-shooting, particularly when addressing performance problems, is to minimise the time and effort you have to spend to get a “good enough” result. A recent question on the...
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