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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:
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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...
Using union and order by clause in mysql
I want to use order by with union in mysql query.
I am fetching different types of record based on different criteria from a table based on distance for a search on my site.
The first select query returns data related to the exact place search .
The 2nd select query returns data related to distance ...
find vs find_by vs where
... suits your needs best.
The find method is usually used to retrieve a row by ID:
Model.find(1)
It's worth noting that find will throw an exception if the item is not found by the attribute that you supply. Use where (as described below, which will return an empty array if the attribute is not f...
Are PHP Variables passed by value or by reference?
Are PHP variables passed by value or by reference?
14 Answers
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