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Applying a function to every row of a table using dplyr?
...o create an appropriately vectorised function.
R provide pmax which is suitable here, however it also provides Vectorize as a wrapper for mapply to allow you to create a vectorised arbitrary version of an arbitrary function.
library(dplyr)
# use base R pmax (vectorized in C)
iris %>% mutate(max...
Rake just one migration
...
To expand on what Ryan says, if the table has been dropped from the database outside of Rails, rake db:migrate:up VERSION=my_version may do nothing, because the schema_migrations table still says it is has been run. In the same situation rake db:migrate:redo VE...
postgresql - sql - count of `true` values
In the above table, if I do :
10 Answers
10
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What should every developer know about databases? [closed]
...r a nontrivial requirement is not a trivial task. You can't build good SQL tables if you misunderstand the relational model.
Physical data modeling is generally DBMS specific, and doesn't need to be learned in much detail, unless the developer is also the database builder or the DBA. What develope...
Finding the id of a parent div using Jquery
...
This can be easily done by doing:
$(this).closest('table').attr('id');
You attach this to any object inside a table and it will return you the id of that table.
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Difference between JOIN and INNER JOIN
...specify CROSS JOIN.
OR
For an inner join, the syntax is:
SELECT ...
FROM TableA
[INNER] JOIN TableB
(in other words, the "INNER" keyword is optional - results are the same
with or without it)
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Why unsigned integer is not available in PostgreSQL?
...ter solution would be Postgres adding unsigned as a first class type. In a table with 20 million records, with and indexed field like this, you are wasting 40MB of space on unused bits. If you are abusing that across another 20 tables, you're now wasting 800MB of space.
– tpart...
Ruby on Rails: how do I sort with two columns using ActiveRecord?
...s, you should use the following more robust version: :order => ["DATE(#{table_name}.updated_at)", :price] (Note that :price is a symbol.)
– Jo Liss
Jul 31 '12 at 17:32
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What data type to use for hashed password field and what length?
...cker gains access to your database, they'd have to construct their rainbow table based on that salt. And that's just as much work as simply guessing the password.
– Bill Karwin
Sep 16 '10 at 7:14
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is of a type that is invalid for use as a key column in an index
...bytes even then so the safest maximum size for your keys would be:
create table [misc_info]
(
[id] INTEGER PRIMARY KEY IDENTITY NOT NULL,
[key] nvarchar(450) UNIQUE NOT NULL,
[value] nvarchar(max) NOT NULL
)
i.e. the key can't be over 450 characters. If you can switch to varchar i...