Tutorial by Examples: b

Let's say we have a table team_person as below: +======+===========+ | team | person | +======+===========+ | A | John | +------+-----------+ | B | Smith | +------+-----------+ | A | Walter | +------+-----------+ | A | Louis | +------+-----------+ | C | ...

RENAME TABLE t TO t_old, t_copy TO t; No other sessions can access the tables involved while RENAME TABLE executes, so the rename operation is not subject to concurrency problems. Atomic Rename is especially for completely reloading a table without waiting for DELETE and load to finish: CREATE ...

A VIEW acts very much like a table. Although you can UPDATE a table, you may or may not be able to update a view into that table. In general, if the SELECT in the view is complex enough to require a temp table, then UPDATE is not allowed. Things like GROUP BY, UNION, HAVING, DISTINCT, and some su...

PHP 5.4+ comes with a built-in development server. It can be used to run applications without having to install a production HTTP server such as nginx or Apache. The built-in server is only designed to be used for development and testing purposes. It can be started by using the -S flag: php -S &lt...

The ROLLUP operator is useful in generating reports that contain subtotals and totals. CUBE generates a result set that shows aggregates for all combinations of values in the selected columns. ROLLUP generates a result set that shows aggregates for a hierarchy of values in the selected col...

R contains a Date class, which is created with as.Date(), which takes a string or vector of strings, and if the date is not in ISO 8601 date format YYYY-MM-DD, a formatting string of strptime-style tokens. as.Date('2016-08-01') # in ISO format, so does not require formatting string ## [1] &quot...

Subqueries come in several flavors, and they have different optimization potential. First, note that subqueries can be either "correlated" or "uncorrelated". Correlated means that they depend on some value from outside the subquery. This generally implies that the subquery mus...

A common problem that leads to an inefficient query goes something like this: SELECT ... FROM a JOIN b ON ... WHERE ... GROUP BY a.id First, the JOIN expands the number of rows; then the GROUP BY whittles it back down the the number of rows in a. There may not be any good c...

// app.module.ts import { NgModule } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { HttpModule } from '@angular/http'; import { MyRootComponent } from './app.component'; @NgModule({ declarations: [MyRootComponent], imports: [BrowserModule, Ht...

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { MyModule } from './app.module'; platformBrowserDynamic().bootstrapModule( MyModule ); In this example, MyModule is the module containing your root component. By bootstrapping MyModule your Angul...

Sometimes we need to perform basic operations like hide/show view based on single value, for that single variable we cannot create model or it is not good practice to create model for that. DataBinding supports basic datatypes to perform those oprations. <layout xmlns:android="http://schema...

First Initialize FirebaseDatabase: FirebaseDatabase database = FirebaseDatabase.getInstance(); Write to your database: // Write a message to the database FirebaseDatabase database = FirebaseDatabase.getInstance(); DatabaseReference myRef = database.getReference("message"); myRef....

NSLog is good, but you can also log by appending to a file instead, using code like: NSFileHandle* fh = [NSFileHandle fileHandleForWritingAtPath:path]; if ( !fh ) { [[NSFileManager defaultManager] createFileAtPath:path contents:nil attributes:nil]; fh = [NSFileHandle fileHandleForWriting...

$ gzip extremelylargefile.txt & $ bg $ disown %1 This allows a long running process to continue once your shell (terminal, ssh, etc) is closed.

The PATH environment variable is generally defined in ~/.bashrc or ~/.bash_profile or /etc/profile or ~/.profile or /etc/bash.bashrc (distro specific Bash configuration file) $ echo $PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/usr/lib/jv...

There are frequent behavior patterns that can result in a lot of boilerplate code. By declaring a method that takes a Closure as a parameter, you can simplify your program. As an example, it is a common pattern to retrieve a database connection, start a transaction, do work, and then either commit ...

To remove a PATH from a PATH environment variable, you need to edit ~/.bashrc or ~/.bash_profile or /etc/profile or ~/.profile or /etc/bash.bashrc (distro specific) file and remove the assignment for that particular path. Instead of finding the exact assignment, you could just do a replacement in t...

<button class="btn btn-default" type="button">Default</button> <button class="btn btn-primary" type="button">Primary</button> <button class="btn btn-success" type="button">Success</button> <button c...

app.ts import {Component} from '@angular/core'; import {Platform, ionicBootstrap} from 'ionic-angular'; import {StatusBar} from 'ionic-native'; import {LoginPage} from './pages/login/login'; import {FIREBASE_PROVIDERS, defaultFirebase, AuthMethods, AuthProviders, firebaseAuthConfig} from 'angul...

Information about a path can be get using the methods of a Path object: toString() returns the string representation of the path Path p1 = Paths.get("/var/www"); // p1.toString() returns "/var/www" getFileName() returns the file name (or, more specifically, the last ...