A few weeks ago Jonathan Lewis has published a note about Tom Kyte’s print_table – a small PL/SQL procedure to output each row in a table as a list of (column_name , value). And since this note has gained some comments with other implementations, here is my contribution. Guess how? Of course with a SQL macro.
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In the last post about SQL macros in 19c I tried to use a subquery as an input for the function. And when I had some DATE calculations in a query, I got ORA-62558: Unsupported data types (DATE) The result looked somewhat confusing at first, but if you think about it, it is logical and maybe not a bug at all. You should just be very explicit while using subqueries and views(!) in this scenario. And because this behavior is not documented, it is worth sharing, I think.
Now that I have created a patched Oracle database docker image with Release Update 19.8 (19.8.0.0.DBRU:200714) to play with, I can finally start testing the backport of SQL macros! (UPDATE: As of now you can play with SQL macros on Autonomous Databases in Oracle Cloud (also free tier!) and on livesql.oracle.com)
SQL Macros have been introduced in Oracle 20c. As of now, Oracle 20c is only available as preview version in Oracle Cloud. That’s why I was quite excited when Connor McDonald pointed out on Twitter that they were backported to 19c. Let’s see if it works, and how.
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More than a year ago I blogged about my view on using Polymorphic Table Function (PTF) for dynamic pivot in Oracle 18c. Actually I was not as optimistic. The solution had at least two significant problems:
With Oracle 20c we now have SQL macros and I was curious, whether they can help here.
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In a previous post on SQL macros in Oracle Database 20c we saw how SQL macros can be used to create a kind of “parameterized” views to establish a simplified access tier to temporal data. In this post I’d like to explore more possibilities to hide the complexity of SQL statements behind a functional syntax provided by using SQL macros. As an example we’ll stay with a temporal data introduced in the previous post and explore how we can do a temporal join of this versioned data.
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Views have always been an efficient tool for encapsulating complex logic, creating defined access structures and so on. But there is one thing views cannot do: accept parameters. And this is unfortunately a big disadvantage in terms of flexibility. As a result, there are a number of workarounds, none of them without their drawbacks.
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In the next post about SQL macros in Oracle 20c we look at how they could be useful for building hash keys. If you are familiar with Data Warehousing and Data Vault modelling approach, you will probably know why it can be a good idea to build hash keys or hash diffs. Anyway, we will not discuss whether or not you should use them, but rather how you can do this in Oracle in a consistent and performant way.
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In this part we will keep focus on scalar macros going into more detail and look at parameter passing and parsing.
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The preview version of Oracle 20c is now available in the cloud and I got the chance to test some new features there. I start with SQL macros, a feature that I think could well become a kind of game changer: let’s just look at the long-awaited parameterized views.
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