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Articles on Trending Technologies
Technical articles with clear explanations and examples
Increment column value 'ADD' with MySQL SET clause
Since the column value ‘ADD’ is already a reserved word, therefore you need to use backticks around the word ADD like `ADD`.Let us see an example and create a table −mysql> create table DemoTable779 ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, `ADD` int ); Query OK, 0 rows affected (0.47 sec)Insert some records in the table using insert command −mysql> insert into DemoTable779(`ADD`) values(54); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable779(`ADD`) values(89); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable779(`ADD`) values(66); Query OK, 1 row affected ...
Read MoreSelect rows from a MySQL table and display using IN()
Let us first create a table −mysql> create table DemoTable778 ( ClientId varchar(100), ClientName varchar(100) ); Query OK, 0 rows affected (1.05 sec)Insert some records in the table using insert command −mysql> insert into DemoTable778 values('J-101', 'John'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable778 values('A-102', 'Adam'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable778 values('C-103', 'Chris'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable778 values('D-104', 'David'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable778 values('R-105', 'Robert'); Query OK, 1 row affected ...
Read MoreMySQL query to display the column and its values using OR in WHERE statement
Let us first create a table −mysql> create table DemoTable777 ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentName varchar(100), StudentAge int ); Query OK, 0 rows affected (1.34 sec)Insert some records in the table using insert command −mysql> insert into DemoTable777(StudentName, StudentAge) values('Chris', 23); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable777(StudentName, StudentAge) values('Robert', 21); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable777(StudentName, StudentAge) values('Mike', 19); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable777(StudentName, StudentAge) values('Bob', 22); Query OK, 1 row ...
Read MoreWhy does the following error occur in MySQL: ERROR 1062 (23000): Duplicate entry?
Let’s say you have set column values as unique key and try to insert duplicate values in the table. This will lead to ERROR 1062 (23000): Duplicate entry.Let us first create a table -mysql> create table DemoTable776 ( FirstValue int, SecondValue int, unique key(FirstValue, SecondValue) ); Query OK, 0 rows affected (0.74 sec)Insert some records in the table using insert command. While inserting duplicate value, the same error arises as shown below -mysql> insert into DemoTable776 values(10, 20); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable776 values(10, 40); Query OK, 1 row affected (0.15 ...
Read MoreHow to check if an URL is valid or not using Java?
The URL class of the java.net package represents a Uniform Resource Locator which is used to point a resource(file or, directory or a reference) in the worldwide web.This class provides various constructors one of them accepts a String parameter and constructs an object of the URL class. While passing URL to this method if you used an unknown protocol or haven’t specified any protocol this method throws a MalformedURLException.Similarly, the toURI() method of this class returns an URI object of the current URL. If the current URL is not properly formatted or, syntactically incorrect according to RFC 2396 this method throws ...
Read MoreRestrictions while declaring a generic (type) in Java
Generics is a concept in Java where you can enable a class, interface and, method, accept all (reference) types as parameters. In other words it is the concept which enables the users to choose the reference type that a method, constructor of a class accepts, dynamically. By defining a class as generic you are making it type-safe i.e. it can act up on any datatype.Restrictions on genericsYou cannot use generics in certain ways and in certain scenarios as listed below −You cannot use primitive datatypes with generics.class Student{ T age; Student(T age){ this.age = age; ...
Read MoreFragment in React.js
Most of the times we need to return multiple elements from a component. React Fragment helps in returning multiple elements. The other alternative is to use a html element like div to wrap them. But using extra html node can cause some semantic issues.Example of React.Fragmentrender() { return ( ); } The short syntax is : render() { return ( ...
Read MoreReact.js stateless vs stateful
Understand the difference in stateless and stateful react componentsIn state management post, we learned how we can handle state in react if something is changed.Stateless components are simple functional component without having a local state but remember there is a hook in react to add state behavior in functional component as well.Stateful component can contains the state object and event handling function, user actions as well.Stateless component are pure in nature which does a very specific task.import React from 'react'; const player = (props) => { return ( I'm a Player: ...
Read MoreContext api in React.js
The React context api is safe to use in production with the version 16.3 or latest. The reason for adding context api is to avoid the passing of props if there is a chain of children components.Without the use of context api, we have to pass the props through all the intermediate components. The other alternative solution is to use third party library such as Redux for maintaining a central store.Understanding the passing of props problemApp.js → props for books → BookList.js → passing the books as props again → Book.jsWith the increase in number of children components, the chain ...
Read MoreWhy need build workflow in React.js
BUILDING A WORK-FLOW HELPS IN DOING BELOW THINGSIt optimizes codeUsing next-gen JavaScript (ES6)Its a standard way for single/multiple page appsProductive approachEasy integration of dependencies with NPM or YarnUse of bundler like web-pack for easier modular code and shipping codePre compiler like BabelWe can use a local development server to test appBuilding workflow looks complex but React community has made it simple for us with a single commandcreate-react-app.To use create-react-app, we will need to have node js install on our machine.You can check if node is installed using below command on terminal −node –versionIf not installed already, please install the latest ...
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