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Order a MySQL table by two columns
How do I sort a MySQL table by two columns?
5 Answers
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How to sum a variable by group
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Using aggregate:
aggregate(x$Frequency, by=list(Category=x$Category), FUN=sum)
Category x
1 First 30
2 Second 5
3 Third 34
In the example above, multiple dimensions can be specified in the list. Multiple aggregated metrics of the same data type can ...
Passing a String by Reference in Java?
... @Boris Pavlovic - yes, but unless the same StringBuilder is used by different threads, which IMO is unlikely in any given scenario, it should not be a problem. It doesn't matter if the method is called by different threads, receiving different StringBuilder.
– Ravi Wa...
How do I pass a unique_ptr argument to a constructor or a function?
...a unique pointer as an argument, as well as their associated meaning.
(A) By Value
Base(std::unique_ptr<Base> n)
: next(std::move(n)) {}
In order for the user to call this, they must do one of the following:
Base newBase(std::move(nextBase));
Base fromTemp(std::unique_ptr<Base>(ne...
How can I multiply and divide using only bit shifting and adding?
...y in terms of adding and shifting you want to decompose one of the numbers by powers of two, like so:
21 * 5 = 10101_2 * 101_2 (Initial step)
= 10101_2 * (1 * 2^2 + 0 * 2^1 + 1 * 2^0)
= 10101_2 * 2^2 + 10101_2 * 2^0
= 10101_2 << 2 + 10101_2 << 0 (De...
Swift how to sort array of custom objects by property value
...t 2
images.sorted({ $0.fileID > $1.fileID })
Swift 3+
images.sorted(by: { $0.fileID > $1.fileID })
The example above gives desc sort order
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PostgreSQL - fetch the row which has the Max value for a column
...uted between 0 and 10k, trans_id uniformly distributed between 0 and 30),
By query cost, below, I am referring to Postgres' cost based optimizer's cost estimate (with Postgres' default xxx_cost values), which is a weighed function estimate of required I/O and CPU resources; you can obtain this by f...
MySQL Query GROUP BY day / month / year
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GROUP BY YEAR(record_date), MONTH(record_date)
Check out the date and time functions in MySQL.
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Windows git “warning: LF will be replaced by CRLF”, is that warning tail backward?
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warning: LF will be replaced by CRLF.
Depending on the editor you are using, a text file with LF wouldn't necessary be saved with CRLF: recent editors can preserve eol style. But that git config setting insists on changing those...
Simply make sure t...
Should I pass a shared_ptr by reference? [duplicate]
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In controlled circumstances you can pass the shared pointer by constant reference. Be sure that nobody is concurrently deleting the object, though this shouldn't be too hard if you're careful about to whom you give references.
In general, you should pass the shared pointer as a strai...