I feel very comfortable with Imperative programming. I never have trouble expressing algorithmically what I want the computer to do once I figured out what is it that I want it to do. But when it comes to languages like SQL or I often get stuck because my head is too used to Imperative programming.
For example, suppose you have the relations band(bandName, bandCountry), venue(venueName, venueCountry), plays(bandName, venueName), and I want to write a query that says: all venueNames such that for every bandCountry there's a band from that country that plays in venue of that name.
Example: I want all the venueNames in which bands from all countries (bandCountry) played. Also, by "relation" I mean an SQL table.
In my mind I immediately go "for each venueName iterate over all the bandCountries and for each bandCountry get the list of bands that come from it. If none of them play in venueName, go to next venueName. Else, at the end of the bandCountries iteration add venueName to the set of good venueNames".
…but you can't talk like that in SQL and I actually need to think about how to formulate this, with the intuitive Imperative solution constantly nagging in the back of my head. Did anybody else had this problem? How did you overcome this? Did you figured out a paradigm shift? Made a map from Imperative concepts to SQL concepts to translate Imperative solutions into Declarative ones? Read a good book?
PS I'm not looking for a solution to the above query, I did solve it.
Best Answer
The idea behind doing things declaratively is that you are supposed to specify what, not how.
To me, it sounds like you're on the right track. The problem isn't that you are thinking about things the wrong way. It's that you're going too far. Let's look at what you're trying to do:
So far, this is great. But then you do this:
In essence, you're doing unnecessary work. You know what you want, which is all you really need. But then you go on and try to figure out how to get it.
If I were you, I'd try to get in the following habit:
It might take some time and effort on your part, but once you really grok declarative programming, it becomes very useful. In fact, you might find yourself using declarative programming in the rest of your code.
If you're looking for a book, I'd recommend SQL and Relational Theory. It really helps you understand the theory behind SQL databases. Just remember to take Date's recommendations with a grain of salt. He gives very good information, but he can be a bit opinionated at times.