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I am no SQL expert, but I always found it a bit weird that selecting the relationships is a relatively hard thing to do for a relational database. What I mean
by duiker101 6y ago
I am no SQL expert, but I always found it a bit weird that selecting the relationships is a relatively hard thing to do for a relational database.
What I mean is that relationships are at the core of the database, so they should--IMHO--be easy. Instead, JOINS feel like some advanced feature that I always see novices struggle with.
- leetrout 6y agoIf not advanced certainly rote and tedious.
- doublesCs 6y agoI don't understand this comment. x JOIN y ON x.id=y.id How is this advanced? The fact that there's an endless number of pitfalls[1] is a characteristic of the operation you're trying to achieve, not a deficiency of SQL. In fact if anything I would say that SQL does a great joke at letting you tweak how you want all those edge cases to be handled. [1] E.g. What happens if some records are missing on one or the other sides of the join? What happens if ids are not unique?
- goto11 6y agoI would be convenient if you could say "x INCLUDE y" or something like that and the engine would figure out the join by foreign/primary keys. Might seem like a small improvement, but if you write lots of queries it would be a significant time saver.
- doublesCs 6y agoIf you do x JOIN y Postgres automatically uses same-name columns for the join. So in the example I gave you, actually "ON x.id=y.id" is redundant. I just added it because if I hadn't someone else would've replied "oh but that only works if you name the columns the same name" Also, in any less than trivial scenario you will have to think how to handle the edge cases. But again, that's a property of the operation, not of the language.
- goto11 6y agoOh yeah, that is a "natural join". Problematic since it depends on the names of the columns. I can see how it is convenient though. I would like something like this, just based on declared foreign key relationships rather than column names.
- doublesCs 6y agoI could say the same thing about your suggestion: Problematic since it depends on what you set as primary/foreign key. I can see how it is convenient though.
- nsonha 6y agoForeign key is a formal semantic while same column name is just a convention
- goto11 6y agoWhat is problematic about that? Column names are just names, there is no guarantee that value in one table corresponds to a value in another table just because the columns have same name. Private/foreign key declarations enforces consistency so it is not possible to have an orphan foreign key.
- rspeele 6y agoAgreed, not just a time-saver but a self-documenting/maintaining advantage. In concept you could change the underlying keys that relate a Foo to a Bar, and still have your queries work. And prevents dumb typos/brainfarts like "join... on Foo.Id = Bar.Id" mistakenly written instead of "on Foo.Id = Bar.FooId".
- 38911BBF 6y agoIMHO lots of teachers have an absolute horrible understanding of relational databases and SQL. Myself included, until I started working at large financial institutions and read every book by Joe Celko I could lay my hands on. E.g. using NATURAL JOINs covers about 1/3 of the use cases where students or apprentices are usually fiddling with INNER JOINs or joining relations using WHERE TableA.ID = TableB.ID, and it's syntax is much simpler. With a well thought out schema, I personally find that NATURAL JOINs covers about 80% of my needs in that respect, and being unable to NATURAL JOIN tables is beginning to indicate well, not a "code smell" but what I would call a "schema smell". I fully agree. Joining relations in a relational databases should absolutely be simple - and it absolutely can be: SELECT col_x, col_y FROM TableA NATURAL JOIN TableB
- duiker101 6y agoThanks for your comment, I actually never heard of NATURAL JOIN, I will have to play with it but it seems very interesting!