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postgresql COUNT(DISTINCT …) very slow
I have a very simple SQL query:
4 Answers
4
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Prefer composition over inheritance?
...ng it to a relational database. It's really hard to map inheritance to the SQL model (you end up with all sorts of hacky workarounds, like creating columns that aren't always used, using views, etc). Some ORMLs try to deal with this, but it always gets complicated quickly. Composition can be easily ...
Creating temporary files in bash
...he file with their own version of the code (like replacing the commands or SQL queries depending on what is being stored).
You could use the following approach to create the temporary directory:
TMPDIR=".${0##*/}-$$" && mkdir -v "$TMPDIR"
or temporary file:
TMPFILE=".${0##*/}-$$" &...
How to do SELECT COUNT(*) GROUP BY and ORDER BY in Django?
...ango 2.1.4). In the example, total is the name given and the count used in sql is COUNT('actor') which in this case doesn't matter, but if e.g. values('x', 'y').annotate(count=Count('x')), you'll get COUNT(x), not COUNT(*) or COUNT(x, y), just tried it in ./manage.py shell
– ti...
MySQL: Transactions vs Locking Tables
...rg/wiki/ACID, en.wikipedia.org/wiki/Isolation_(database_systems) and dev.mysql.com/doc/refman/5.1/en/…
– Nikola Svitlica
Sep 6 '15 at 21:52
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Remove duplicate rows in MySQL
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This is no longer support in 5.7.4, dev.mysql.com/doc/refman/5.7/en/alter-table.html
– Ray Baxter
Nov 25 '15 at 20:59
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Does Redis persist data?
... power outage..). Redis trades data safety versus performance, like most NoSQL-DBs do.
Most NoSQL-databases follow a concept of replication among multiple nodes to minimize this risk. Redis is considered more a speedy cache instead of a database that guarantees data consistency. Therefore its use c...
switch / pattern matching idea
...s or other involved (often heavily generic) code blocks. Extending LINQ-to-SQL fits in here too.
Tuples, to some extent.
** But do note: The lack of automatic generalization and type inference really hinder the use of even these features. **
All this said, as someone else mentioned, on a small t...
Difference between attr_accessor and attr_accessible
... "users" that contains three columns "firstname", "lastname" and "role" :
SQL instructions :
CREATE TABLE users (
firstname string,
lastname string
role string
);
I assumed that you set the option config.active_record.whitelist_attributes = true in your config/environment/production.rb to ...
windows service vs scheduled task
...ication. OR .. they are continuously-running heavyweight applications like SQL Server, BizTalk, RPC Connections, IIS (even though IIS technically offloads work to other processes).
Personally, I favour scheduled tasks over Window Services for repititive maintenance tasks and applications such as fi...