If you’re working with collections you sometimes need to know if some value is a member of it. Fortunately, Oracle provided the very useful member of function, it’s highly optimised and will out-perform other methods Continue reading
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….
Adding string data to a CLOB in Oracle can be a tad slow, when compared to other string concatenation situations. I first became aware of this concatenation performance issue from my own coding experience, but also from threads on Oracle Technical Network and a blog post by Jonathan Lewis.
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 184.108.40.206.0. 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
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.
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.
Occasionally I see posts on Oracle sites from users asking how to create a view based on parameter(s). Now, many would ask why would you’d need this, especially when you can simply select from the view and apply a where clause? Well, there are a few situations which fall outside of that approach, the commonest it probably that the view contains a function that needs parameters or the view requires some “state” in its operation (state means there is memory of the past). Anyway, assuming you have such a need let’s look at some of the approaches at our disposal.