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multiprocessing.Pool: When to use apply, apply_async or map?
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Here is an overview in a table format in order to show the differences between Pool.apply, Pool.apply_async, Pool.map and Pool.map_async. When choosing one, you have to take multi-args, concurrency, blocking, and ordering into account:
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Order a MySQL table by two columns
How do I sort a MySQL table by two columns?
5 Answers
5
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Easiest way to rename a model using Django/South?
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To answer your first question, the simple model/table rename is pretty straightforward. Run the command:
./manage.py schemamigration yourapp rename_foo_to_bar --empty
(Update 2: try --auto instead of --empty to avoid the warning below. Thanks to @KFB for the tip.)
If ...
Can I protect against SQL injection by escaping single-quote and surrounding user input with single-
...rmissions in the database to executing the needed SPs only, and not access tables directly.
you can also easily verify that the entire codebase only accesses the DB through SPs...
share
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improve ...
What's the Hi/Lo algorithm?
...re out the next identifier value knowing we use hilo in this particular DB table?
– Vlad Mihalcea
Feb 7 '17 at 1:46
My...
How to trim a string in SQL Server before 2017?
...ou add database constraints to prevent bad data in the future e.g.
ALTER TABLE Customer ADD
CONSTRAINT customer_names__whitespace
CHECK (
Names NOT LIKE ' %'
AND Names NOT LIKE '% '
AND Names NOT LIKE '% %'
);
Also consider disallowing...
'Incomplete final line' warning when trying to read a .csv file into R
...here's no way that in your case the warning was thrown by the function readTableHeader, because that one doesn't read the final line. Hence your problem is not the same as that of the OP.
– Joris Meys
May 1 at 11:31
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Rails: Using greater than/less than with a where statement
...non discrete values or columns where you can't use the + 1 strategy.
Arel table
If you want to get fancy you can make use of the Arel::Table.
User.where(User.arel_table[:id].gt(200))
will generate the SQL
"SELECT `users`.* FROM `users` WHERE (`users`.`id` > 200)"
The specifics are as foll...
What are the use cases for selecting CHAR over VARCHAR in SQL?
... Another reason is page splits and fragmentation. I had a table with an IDEN PK that got 99% fragmented because of page splits on varchar columns. A very active table and by nature of the application a new row empty row would get created and then populated. Char fixed the fragme...
PostgreSQL LIKE query performance variations
...large variation in response times regarding LIKE queries to a particular table in my database. Sometimes I will get results within 200-400 ms (very acceptable) but other times it might take as much as 30 seconds to return results.
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