Tutorial by Examples: di

The AND keyword is used to add more conditions to the query. NameAgeGenderSam18MJohn21MBob22MMary23F SELECT name FROM persons WHERE gender = 'M' AND age > 20; This will return: NameJohnBob using OR keyword SELECT name FROM persons WHERE gender = 'M' OR age < 20; This will return: n...

When working with existing model that is quite big and is being regenerated quite often in cases where abstraction needed it might be costly to manually go around redecorating model with interfaces. In such cases one might want to add some dynamic behavior to model generation. Following example wil...

SELECT name, caption as title, year, pages FROM books UNION SELECT name, title, year, 0 as pages FROM movies When combining 2 record sets with different columns then emulate the missing ones with default values.

Use the yum command to manage packages in Enterprise Linux-based operating systems: yum install php This installs a minimal install of PHP including some common features. If you need additional modules, you will need to install them separately. Once again, you can use yum to search for these pac...

You can use the header() function to instruct the browser to redirect to a different URL: $url = 'https://example.org/foo/bar'; if (!headers_sent()) { // check headers - you can not send headers if they already sent header('Location: ' . $url); exit; // protects from code being executed afte...

To display "Some Text", use the command: echo Some Text This will output the string Some Text followed by a new line. To display the strings On and Off (case insensitive) or the empty string, use a ( instead of white-space: echo(ON echo( echo(off This will output: ON off ...

Sometimes you may need additional features from a directive. Instead of rewriting (copy) the directive, you can modify how the directive behaves. The decorator will be executed during $inject phase. To do so, provde a .config to your module. The directive is called myDirective, so you have to con...

Angular js directives can be nested or be made interoperable. In this example, directive Adir exposes to directive Bdir it's controller $scope, since Bdir requires Adir. angular.module('myApp',[]).directive('Adir', function () { return { restrict: 'AE', controlle...

We can read from a text file: dt <- fread("my_file.csv") Unlike read.csv, fread will read strings as strings, not as factors by default. See the [topic on fread][need_a_link] for more examples.

For efficiency, data.table offers a way of altering a data.frame or list to make a data.table in-place: # example data.frame DF = data.frame(x = letters[1:5], y = 1:5, z = (1:5) > 3) # modification setDT(DF) Note that we do not <- assign the result, since the object DF has been modifi...

# example data DT = data.table(Titanic) Suppose we want to see each class only if a majority survived: DT[, if (sum(N[Survived=="Yes"]) > sum(N[Survived=="No"]) ) .SD, by=Class] # Class Sex Age Survived N # 1: 1st Male Child No 0 # 2: 1st Fema...

The DISTINCT clause after SELECT eliminates duplicate rows from the result set. CREATE TABLE `car` ( `car_id` INT UNSIGNED NOT NULL PRIMARY KEY, `name` VARCHAR(20), `price` DECIMAL(8,2) ); INSERT INTO CAR (`car_id`, `name`, `price`) VALUES (1, 'Audi A1', '20000'); INSERT INTO CA...

Monotonic predicates can be debugged by applying declarative reasoning. In pure Prolog, a programming mistake can lead to one or all of the following phenomena: the predicate incorrectly succeeds in a case where it should fail the predicate incorrectly fails in a case where it should succeed t...

Examples of monotonic predicates are: unification with (=)/2 or unify_with_occurs_check/2 dif/2, expressing disequality of terms CLP(FD) constraints like (#=)/2 and (#>)/2, using a monotonic execution mode. Prolog predicates that only use monotonic goals are themselves monotonic. Monoton...

Here are examples of predicates that are not monotonic: meta-logical predicates like var/1, integer/1 etc. term comparison predicates like (@<)/2 and (@>=)/2 predicates that use !/0, (\+)/1 and other constructs that break monotonicity all-solutions predicates like findall/3 and setof/3. ...

Adding a footer is not natively possible. Luckily, we can make use of jQuery and CSS to add a footer to the slides of an ioslides presentation rendered with knitr. First of all we have to include the jQuery plugin. This is done by the line <script src="https://ajax.googleapis.com/ajax/libs...

Sometimes one has to work with pages that are not using jQuery while most developers are used to have jQuery handy. In such situations one can use Chrome Developer Tools console (F12) to manually add jQuery on a loaded page by running following: var j = document.createElement('script'); j.onload ...

Modifiers are a way to indicate how external objects can access an object's data. Public Means any object can access this without restriction Private Means only the declaring object can access and view this Protected Means only the declaring object and any object that inherits from...

Static method: Dim parseMethod = GetType(Integer).GetMethod("Parse",{GetType(String)}) Dim result = DirectCast(parseMethod.Invoke(Nothing,{"123"}), Integer) Instance method: Dim instance = "hello".ToUpper Dim method = Gettype(String).GetMethod("ToUpper&quo...

ArrayList is one of the inbuilt data structures in Java. It is a dynamic array (where the size of the data structure not needed to be declared first) for storing elements (Objects). It extends AbstractList class and implements List interface. An ArrayList can contain duplicate elements where it mai...