snippets

Presenting “Analytic Functions in Practice” at the DOAG-Regio Hamburg/Nord Dec 4 2018


Save the date to see my presentation about “Oracle Analytic Functions in Practice Applications” along the regular meetup of the DOAG/Oracle-community in Hamburg on Dec 4 2018. Although analytic functions is nothing really new in the Oracle world, I’m again attempting to propagate the thrilling productivity of this SQL-toolset, since practice applications are still not as dispersed as expected. To this extent, I want to stress windowing and aggregation over analytics and statistics in real world scenarios and examples. The presentation will be held in German, I suppose. Event details go here and there:

A Confluence dashboard-like page layout using section-, column- and panel-macros

Every wiki landing page usually features a kind of overview layout to provide links to the most interesting topics or articles. This might constitute a classic table of contents, quite lengthy at times, a tag cloud of the hottest keywords (and relations, maybe), for iterative exploration, or, if you like, a dashboard of context grouped / block visualized widgets of important articles. Whatever you prefer, me, I almost always take on the dashboard approach, because it provides a great productivity in information to space ratio. Furthermore, dashboards also greatly serve the figurative memory in that one can plainly remember some article link resides in a widget up in the upper right corner of the page or yet within another widget with an outstanding background color.

However, I’m not planning to advertise dashboard / widget user interfaces here. What is to follow comprises an implementation pattern and example of setting up a simple dashboard layout in recent Confluence environments. All you need is to employ section-, column- and panel-macros in that order and hierarchy, respectively. For reference see the latest Confluence docs concerning:

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Flashback version query and the proper use of timestamp and scn clauses

Flashback version query essentially enables you to lookup the incarnations of a row (defined by primary key) in the past, in a consecutive manner. Version information is depicted by a couple of pseudo-columns, namely versions_xid, versions_startscn, versions_endscn, versions_starttime, versions_endtime and versions_operation. See Using Oracle Flashback Version Query in the docs for explanations.

In combination with flashback query or flashback transaction query, one may restore a row incarnation from the past into a new table or even rollback to a past row incarnation within the same table.

This article will discuss flashback version query together with flashback query to restore one to many rows, just shown for a row of a unique key here for brevity, detailing when and when not to use timestamp and scn select where clauses to prevent pitfalls. An example table / dataset will be given, representing a real world scenario where some past data needs to be identified first and is then to be made available again.

Flashback version query uses the following pattern, including the pseudo-columns introduced above, on an actual application-, but not a system-table (alike flashback transaction query). A timestamp– or scn-range must be supplied to define the lookup window (defined by the stock of the available undo-data, remember) and to actually populate the pseudo-columns, respectively:

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Getting a raw constant number of rows from oracle’s table sample function

You may of course know these two famous posts called To sample or not to sample… (part-2) about data sampling by Mark Hornick. Although very limited in scope, the two posts (imho) very well sketch why we may employ data sampling and how we may lift off table sampling in oracle.
In general, sampling is used to make a representative statement about a collection of data while only regarding a limited random selection, the sample. As long as you are ok to analyze just a sufficient subset of your 1o million rows table for an analysis, you will save your environment a lot of resources and time. On some other scenario, a limited random data selection may also serve verification or testing purposes where, however, not the representativeness but the randomness at a more or less constant sample size, determines the quality of the sample output. Again, as long as you are ok to not exceed this 15 minutes time window overnight, you will be allowed to run that live unit test on any table in question, on 1, 10 or 100 million rows.
In sql, selecting in regard to gain a representative statement will feed the sample function with a requested percentage of rows to sample from. This is what the oracle sample function already offers. Yet another sql to accept a requested actual number of rows to return, independent of the table size, is not available so far (although most people do expect exactly this behaviour when they spot the sql sample function for the first time, weird). The following text will outline a snippet of pl/sql to provide for a sample function to accept the expected number of rows as a parameter.

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