GCD provides mechanism for performing a loop, whereby the loops happen concurrently with respect to each other. This is very useful when performing a series of computationally expensive calculations.
Consider this loop:
for index in 0 ..< iterations {
// Do something computationally expens...
A powerful alternative to virtualenv is Anaconda - a cross-platform, pip-like package manager bundled with features for quickly making and removing virtual environments. After installing Anaconda, here are some commands to get started:
Create an environment
conda create --name <envname> pyth...
Applying a function to a collection/stream and creating a new collection/stream is called a projection.
/// Projection
var newReleases = [
[
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images...
Create a stream by selecting the elements from a stream that pass a certain condition is called filtering
var newReleases = [
[
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.j...
Query syntax and method syntax are semantically identical, but many people find query syntax simpler and easier to read. Let’s say we need to retrieve all even items ordered in ascending order from a collection of numbers.
C#:
int[] numbers = { 0, 1, 2, 3, 4, 5, 6 };
// Query syntax:
IEnumerab...
A HAVING clause filters the results of a GROUP BY expression. Note: The following examples are using the Library example database.
Examples:
Return all authors that wrote more than one book (live example).
SELECT
a.Id,
a.Name,
COUNT(*) BooksWritten
FROM BooksAuthors ba
INNER JOIN Aut...
We can use 1,2,3.. to determine the type of order:
SELECT * FROM DEPT
ORDER BY
CASE DEPARTMENT
WHEN 'MARKETING' THEN 1
WHEN 'SALES' THEN 2
WHEN 'RESEARCH' THEN 3
WHEN 'INNOVATION' THEN 4
ELSE 5
END,
CITY
IDREGIONCITYDEPARTMENTEMPLOYEES_N...
PostgreSQL and SQLite
To create a temporary table local to the session:
CREATE TEMP TABLE MyTable(...);
SQL Server
To create a temporary table local to the session:
CREATE TABLE #TempPhysical(...);
To create a temporary table visible to everyone:
CREATE TABLE ##TempPhysicalVisibleToEveryo...
When results need to have some logic applied 'on the fly' one can use CASE statement to implement it.
SELECT CASE WHEN Col1 < 50 THEN 'under' ELSE 'over' END threshold
FROM TableName
also can be chained
SELECT
CASE WHEN Col1 < 50 THEN 'under'
WHEN Col1 > 50 AND Col1 ...
Sometimes when tables are used mostly (or only) for reads, indexing does not help anymore and every little bit counts, one might use selects without LOCK to improve performance.
SQL Server
SELECT * FROM TableName WITH (nolock)
MySQL
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;...
Sometimes one wants to capture the records that have just been updated.
CREATE TABLE #TempUpdated(ID INT)
Update TableName SET Col1 = 42
OUTPUT inserted.ID INTO #TempUpdated
WHERE Id > 50
WITH cte AS (
SELECT ProjectID,
ROW_NUMBER() OVER (PARTITION BY ProjectID ORDER BY InsertDate DESC) AS rn
FROM ProjectNotes
)
DELETE FROM cte WHERE rn > 1;
The Kernel#require method will load files only once (several calls to require will result in the code in that file being evaluated only once). It will search your ruby $LOAD_PATH to find the required file if the parameter is not an absolute path. Extensions like .rb, .so, .o or .dll are optional. Re...
The method Kernel#autoload registers filename to be loaded (using Kernel::require) the first time that module (which may be a String or a symbol) is accessed.
autoload :MyModule, '/usr/local/lib/modules/my_module.rb'
The method Kernel#autoload? returns filename to be loaded if name is registere...
When files are not available, the require family will throw a LoadError. This is an example which illustrates loading optional modules only if they exist.
module TidBits
@@unavailableModules = []
[
{ name: 'CoreExtend', file: 'core_extend/lib/core_extend' } \
, { name: 'Fs' ...
The Kernel#load method will evaluate the code in the given file. The search path will be constructed as with require. It will re-evaluate that code on every subsequent call unlike require. There is no load_relative.
load `somefile`
You can use any ruby technique to dynamically create a list of files to load. Illustration of globbing for files starting with test, loaded in alphabetical order.
Dir[ "#{ __dir__ }**/test*.rb" ) ].sort.each do |source|
require_relative source
end
To get records having any of the given ids
select *
from products
where id in (1,8,3)
The query above is equal to
select *
from products
where id = 1
or id = 8
or id = 3
