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How to create a MySQL hierarchical recursive query
... (select @pv := '19') initialisation
where find_in_set(parent_id, @pv)
and length(@pv := concat(@pv, ',', id))
Here is a fiddle.
Here, the value specified in @pv := '19' should be set to the id of the parent you want to select all the descendants of.
This will work also if a parent has m...
Checking for a dirty index or untracked files with Git
...;/dev/null| grep "^M" | wc -l)
# Get number of files that are uncommitted and not added
expr $(git status --porcelain 2>/dev/null| grep "^ M" | wc -l)
# Get number of total uncommited files
expr $(git status --porcelain 2>/dev/null| egrep "^(M| M)" | wc -l)
Note: The 2>/dev/null filters...
Running multiple commands with xargs
In the example above, xargs takes echo % as the command argument. But in some cases, I need multiple commands to process the argument instead of one. For example:
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Function pointers, Closures, and Lambda
I am just now learning about function pointers and, as I was reading the K&R chapter on the subject, the first thing that hit me was, "Hey, this is kinda like a closure." I knew this assumption is fundamentally wrong somehow and after a search online I didn't find really any analysis of this compari...
How can I view array structure in JavaScript with alert()?
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EDIT: Firefox and Google Chrome now have a built-in JSON object, so you can just say alert(JSON.stringify(myArray)) without needing to use a jQuery plugin. This is not part of the Javascript language spec, so you shouldn't rely on the JSO...
Grouped LIMIT in PostgreSQL: show the first N rows for each group?
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For those who works with like millions rows and seeks for really performant way to do this - poshest's answer is the way to go. Just dont forget to spice ti up with proper indexing.
– Diligent Key Presser
Jun 20 '19 at 8:46
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Is it possible to use global variables in Rust?
...t spawn. The upside is that unlike truly global state, it is entirely safe and is not a pain to use - true global state is a massive pain in any language. Here's an example:
extern mod sqlite;
use std::cell::RefCell;
thread_local!(static ODB: RefCell<sqlite::database::Database> = RefCell::n...
Precise Financial Calculation in JavaScript. What Are the Gotchas?
...ication in JavaScript. The calculations required involve compound interest and relatively long decimal numbers. I'd like to know what mistakes to avoid when using JavaScript to do this type of math—if it is possible at all!
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How do I pass a unique_ptr argument to a constructor or a function?
I'm new to move semantics in C++11 and I don't know very well how to handle unique_ptr parameters in constructors or functions. Consider this class referencing itself:
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How to select multiple rows filled with constants?
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I used this with SQL Server and it worked, but I had to use AS to give aliases on the first SELECT
– Sled
May 18 '17 at 18:34
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