Create Structured Nested XML from Flat Data

Imagine you’ve been given the task to create an XML document which is structured according to nested level of detail, but the data source is unstructured flat data, it’s not normalised, not extracted to the relevant third normal form. It might be coming from a view, query, an external table, a spreadsheet, some legacy table etc. Anyway, you get the idea.

In other words, convert this…


        ID FIRST_NAME           LAST_NAME                   AGE CITY                 REGION                    COUNTRY
---------- -------------------- -------------------- ---------- -------------------- ------------------------- --------------------
         1 Zsazsa               Piniur                       46 Hamburg              Hamburg                   Germany
         2 Chane                Frise                        41 Düsseldorf           Nordrhein-Westfalen       Germany
         3 Brandon              Fishbourn                    41 Manchester           England                   United Kingdom
         4 Hulda                Sepey                        31 Dortmund  

-- SNIP....

Into this….

<COUNTRIES>
  <COUNTRY NAME="....">
    <REGIONS>
      <REGION NAME="....">
        <CITIES>
          <CITY NAME="....">
            <RESIDENTS>
              <RESIDENT>....

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Nvl versus Coalesce, and the winner is…

Most Oracle developers I know use NVL, rather than COALESCE for returning the first not null value of two arguments.  Most will cite it’s for habitual, historic reasons (COALESCE was introduced later in Oracle’s history) or because it’s shorter to type.

Well NVL and COALESCE do the same thing anyway, so why would I change?

Well, there’s one very good reason why you should the SQL standards function COALESCE over Oracle’s proprietary NVL….
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Recursive Subquery Factoring Date Bug in 11gR2

Since Oracle 11gR2, Oracle has supported Recursive Subquery Factoring – this is a more flexible way of doing recursive queries than Oracle’s Connect By. Although 11g is quite old now, it’s still being used in earnest.  Whilst writing some code recently, I noticed there appears to be a problem with them regarding dates. I found this in version 11.2.0.2.0. Let’s take a look at what I found…

with t1(a_date) as (
  select date '2018-12-26'
  from   dual
  union all
  select a_date + 1 -- Problem here
  from   t1
  where a_date + 1 < date '2018-12-30'
)
select * from t1

Error at line 5
ORA-01790: expression must have same datatype as corresponding expression

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Faster Decimal to Binary Function

There was recently a post on the Oracle forums by a person who needed to convert decimal values to a binary string. They had found the standard library PL/SQL function that you often see on Oracle sites, but its slow performance was giving him headaches. It was an interesting thread as many people offered solutions, and it showed the ingenuity of people, in coming up with alternatives. In this article I’ll show some of my efforts, and my final function which, to my pleasure, was the fastest in the thread.
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Inheriting Values in SQL

Imagine a situation where you have hierarchical data with various values and you wanted to inherit values from ancestors if a given level in the hierarchy had null values. So if a level had a null value, it could inherit that missing value from the parent and if the parent didn’t have a value, the grandparent etc. etc. updwards until we reach the root. How would you do it?  Well in this article I’ll explore a few approaches.
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