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Using group by on multiple columns
I understand the point of GROUP BY x .
2 Answers
2
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Are arrays passed by value or passed by reference in Java? [duplicate]
...itive type in Java, but they are not objects either , so are they passed by value or by reference? Does it depend on what the array contains, for example references or a primitive type?
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How to sort an array in descending order in Ruby
... on the various suggested answers. Here's what I found out:
#!/usr/bin/ruby
require 'benchmark'
ary = []
1000.times {
ary << {:bar => rand(1000)}
}
n = 500
Benchmark.bm(20) do |x|
x.report("sort") { n.times { ary.sort{ |a,b| b[:bar] <=> a[:bar] } } }
x.repor...
MySQL “Group By” and “Order By”
...o be able to select a bunch of rows from a table of e-mails and group them by the from sender. My query looks like this:
6...
What's faster, SELECT DISTINCT or GROUP BY in MySQL?
...e the same, a query optimizer would have to catch the fact that your GROUP BY is not taking advantage of any group members, just their keys. DISTINCT makes this explicit, so you can get away with a slightly dumber optimizer.
When in doubt, test!
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Call by name vs call by value in Scala, clarification needed
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The example you have given only uses call-by-value, so I will give a new, simpler, example that shows the difference.
First, let's assume we have a function with a side-effect. This function prints something out and then returns an Int.
def something() = {
print...
PostgreSQL DISTINCT ON with different ORDER BY
... [...] Note that the "first row" of each set is unpredictable unless ORDER BY is used to ensure that the desired row appears first. [...] The DISTINCT ON expression(s) must match the leftmost ORDER BY expression(s).
Official documentation
So you'll have to add the address_id to the order by.
Alt...
MySQL order by before group by
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Using an ORDER BY in a subquery is not the best solution to this problem.
The best solution to get the max(post_date) by author is to use a subquery to return the max date and then join that to your table on both the post_author and the ...
SQLAlchemy ORDER BY DESCENDING?
How can I use ORDER BY descending in a SQLAlchemy query like the following?
6 Answers
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Is JavaScript a pass-by-reference or pass-by-value language?
The primitive types (number, string, etc.) are passed by value, but objects are unknown, because they can be both passed-by-value (in case we consider that a variable holding an object is in fact a reference to the object) and passed-by-reference (when we consider that the variable to the object hol...