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When should I use a composite index?
...To create a friends' tables (i.e. for a social network) we need 2 columns: user_id, friend_id.
Table Strcture
user_id (medium_int)
friend_id (medium_int)
Primary Key -> (user_id, friend_id)
By virtue, a Primary Key (PK) is unique and by creating a composite PK, Innodb will automatically chec...
Setting Environment Variables for Node to retrieve
...les (in this case) are being used to pass credentials to your application. USER_ID and USER_KEY can both be accessed from process.env.USER_ID and process.env.USER_KEY respectively. You don't need to edit them, just access their contents.
It looks like they are simply giving you the choice between l...
MySQL Insert into multiple tables? (Database normalization?)
...00.com');
full script:
drop table if exists users;
create table users
(
user_id int unsigned not null auto_increment primary key,
username varchar(32) unique not null
)
engine=innodb;
drop table if exists user_profile;
create table user_profile
(
profile_id int unsigned not null auto_increment p...
Increment value in mysql update query
...l_query("
UPDATE member_profile
SET points = points + 1
WHERE user_id = '".$userid."'
");
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Rest with Express.js nested router
...(function(req, res) {})
.post(function(req, res) {})
userRouter.route('/:user_id')
.get(function() {})
itemRouter.route('/')
.get(function(req, res) {})
.post(function(req, res) {})
itemRouter.route('/:item_id')
.get(function(req, res) {
return res.send(req.params);
});
app.use('/u...
MySQL join with where clause
...s.category_id = categories.category_id
and user_category_subscriptions.user_id =1
See, with an inner join, putting a clause in the join or the where is equivalent. However, with an outer join, they are vastly different.
As a join condition, you specify the rowset that you will be joining to t...
Add a reference column migration in Rails 4
...ake db:migrate.
This migration will take care of adding a new column named user_id to uploads table (referencing id column in users table), PLUS it will also add an index on the new column.
UPDATE [For Rails 4.2]
Rails can’t be trusted to maintain referential integrity; relational databases come...
Pandas aggregate count distinct
...
How about either of:
>>> df
date duration user_id
0 2013-04-01 30 0001
1 2013-04-01 15 0001
2 2013-04-01 20 0002
3 2013-04-02 15 0002
4 2013-04-02 30 0002
>>> df.groupby("date").agg({"duration": np.sum, ...
Facebook database design?
... Schema:
CREATE TABLE IF NOT EXISTS `friends` (
`id` int(11) NOT NULL,
`user_id` int(11) NOT NULL,
`friend_id` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
Friends of Friends Query:
(
select friend_id
from friends
where user_id = 1
) uni...
Sanitizing strings to make them URL and filename safe?
...e server or client. From the PHP docs:
A "word" character is any letter or digit or the underscore character, that is, any character which can be part of a Perl "word". The definition of letters and digits is controlled by PCRE's character tables, and may vary if locale-specific matching i...