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What's the difference between an id and a class?
...fic element and class when you have a number of things that are all alike. For instance, common id elements are things like header, footer, sidebar. Common class elements are things like highlight or external-link.
It's a good idea to read up on the cascade and understand the precedence assigned to...
Efficiently convert rows to columns in sql server
I'm looking for an efficient way to convert rows to columns in SQL server, I heard that PIVOT is not very fast, and I need to deal with lot of records.
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In an array of objects, fastest way to find the index of an object whose attributes match a search
...lementPos = array.map(function(x) {return x.id; }).indexOf(idYourAreLookingFor);
var objectFound = array[elementPos];
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How to efficiently build a tree from a flat structure?
... property does not necessarily matches with an ID in the structure. Therefore their could be several trees emerging from these objects.
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Retrieving the last record in each group - MySQL
... FROM ranked_messages WHERE rn = 1;
Below is the original answer I wrote for this question in 2009:
I write the solution this way:
SELECT m1.*
FROM messages m1 LEFT JOIN messages m2
ON (m1.name = m2.name AND m1.id < m2.id)
WHERE m2.id IS NULL;
Regarding performance, one solution or the o...
What is the most efficient/elegant way to parse a flat table into a tree?
...t can be stored in the same table too. Read "Trees and Hierarchies in SQL for Smarties" by Joe Celko for a lot more information on these designs.
I usually prefer a design called Closure Table (aka "Adjacency Relation") for storing tree-structured data. It requires another table, but then queryin...
Build tree array from flat array in javascript
...n efficient solution if you use a map-lookup. If the parents always come before their children you can merge the two for-loops. It supports multiple roots. It gives an error on dangling branches, but can be modified to ignore them. It doesn't require a 3rd-party library. It's, as far as I can tell, ...
What is the difference between id and class in CSS, and when should I use them? [duplicate]
...ere I gave an id to the div element and it's applying the relevant CSS for it.
15 Answers
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How to get ID of the last updated row in MySQL?
...nt which will set the value returned by the next call to LAST_INSERT_ID(). For example: UPDATE table SET id=LAST_INSERT_ID(id), row='value' WHERE other_row='blah';. Now, SELECT LAST_INSERT_ID(); will return the updated id. See newtover's answer for more details.
– Joel
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Correct way to pass multiple values for same parameter name in GET request
I'm looking into what is the correct way to pass multiple values for the same parameter name in a GET request.
4 Answers
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