These examples reminded me one more issue: change in column selection, might change number of rows,
which means column addition/removal is so much riskier afair.
> Not if distinct is the default.
If that works for you, great, but let’s agree to disagree here.
Performance implication exist, but it is secondary.
Primary reason:
distinct on every select shows either lack of knowledge of schema, in particular which columns make rows unique, or unfortunate schema design.
(Apart from niche cases, schema should be somewhat normal. I.e. column parent_name belongs in the table parent, not in the table student)
Select a from x where myuniquekey=1; —- guaranted to return 1 or zero rows, if myuiniquekey is actually unique.
Select a from x join y on x.parent_id = y.y_id —- guaranteed to return same amount of rows as exist in y, never more, never duplicates y rows. (N-to-1 relation)
If distinct is used in any of above, then question “why?” naturally arises.
In more severe case, leads to bugs:
Select distinct student.student_name, parent.parent_name from student join parent on student.parent_id = parent.parent_id —- silently discards rows, where by accident student/parent name combo matches several times.
Technically sql allows comparing unrelated columns (colour=last_name), but for vast majority of cases, when joining, one of the side should be joined using it’s unique key, and other side should be using it’s foreign key, which ensures that duplicates don’t appear randomly, and thus distinct is not needed.
Problem is that despots want power, whatever system you have you will get despots wanting to be at the top, and doing what is necessary to get there. Democracy at least moves them around a bit.
I’ve read something like: there are bunch of observations of extremely dense masses in various suroundings. Talented people can find explanations other than black holes in each case.
But that feels adhoc, and black hole fits quite nicely for whole class of observations. Current consensus is that b holes exist.
On its own, seeing ‘SQLException‘ in method signature, does not provide you with information: “this is part of bigger transaction, and you have ability and responsibility to retry or rollback”.
That will be part of lib documentation, which should be read & understood regardless of existence of checked exception.
Yes, grep and nuclear reactor controller, and your gui grep are applications.
They all use library for file reading.
As author of file reading library you don’t know how critical is the failure to open a file or how it should be handled. My point was that You know those things only at application level.
So it feels a bit misguided to decide at library level which failures are important. (I.e. which are checked vs which are unchecked)
> But as API authors how can we make sure
First thought: documentation. (which is required for both, checked and unchecked exceptions).
But overall, it’s not library author’s responsibility or ability to “ensure”. You can’t force correct handling of exception. At best one can make it a bit more annoying to ignore, and convenient to do the right thing.
My view:
- all exceptions should be unchecked
- assume all code throws
- if “log and exit/continue” is not enough and you need to know exact exception types, dig into the docs.
Possibly there should be emergency scenarios considered. Where government turns off video things (youtube and netflix) in case of major network degradation.
> Not if distinct is the default.
If that works for you, great, but let’s agree to disagree here.