Things I wished more developers knew about databases

Re:Things I wished more developers knew about databases by sk5t on Wednesday April 22, 2020 @11:26AM (#22946553)

A more functional mindset can definitely help here. Think of your "sales per day" model in terms of starting with a sequence of days--startingDay up to startingDay + n--as the input to a function that maps to an aggregate of that day's activity.

Aggregate functions in SQL are IMHO quite awesome once you develop a comfort level to stop worrying about them per se. I wouldn't like to try to get Excel to tell me--or write the code to do manually--something like "show me the standard deviation in units sold by day of week over the last ten summers."

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Re:Things I wished more developers knew about databases by pbowyer on Wednesday April 22, 2020 @11:46AM (#22946799)

I find thinking about analytic queries like these as map/filter/reduce easier than thinking in terms of the SQL!

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Re:Things I wished more developers knew about databases by taffer on Wednesday April 22, 2020 @12:31PM (#22947358)

SQL and functional programming constructs are actually quite similar:

SELECT -> map

FROM -> stream

JOIN -> flatMap

WHERE -> filter

GROUP BY -> collect

ORDER BY -> sorted

https://blog.jooq.org/2015/08/13/common-sql-clauses-and-thei...

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Re:Things I wished more developers knew about databases by karmakaze on Wednesday April 22, 2020 @09:21PM (#22951905)

I don't see how JOIN is like flatMap. It's a subset of a cross-product. It's more like do-notation:

  x <- ..
  y <- ..
  return (x, y)

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Re:Things I wished more developers knew about databases by taffer on Thursday April 23, 2020 @04:15AM (#22953825)

> I don't see how JOIN is like flatMap

This is explained in the blog post I linked, including an example.

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Re:Things I wished more developers knew about databases by karmakaze on Thursday April 23, 2020 @03:38PM (#22960229)

It's really flatMap/map from the link:

  List<Integer> s1 = Stream.of(1, 2);
  Supplier<Stream<String>> s2 = ()->Stream.of("A", "B");

  s1.flatMap(v1 -> s2.get()
                   .map(v2 -> tuple(v1, v2)))
    .forEach(System.out::println);

That's just a nested loop.

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