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Articles on Trending Technologies
Technical articles with clear explanations and examples
React.js memo function in functional component
We have shouldComponentUpdate in class based component as lifecycle method. This method can be used to achieve the performance optimization by comparing props (previous and next) and executing render conditionally .We have React.PureComponent as well which can do shallow comparison of state and props. But in functional component we don’t have such methods.Now, React has provided a memo method which will do the same functionality for the functional components.const functionalComponent = React.memo(function functionalComponent(props) { /* render using props */ });We have wrapped the component inside the memo method. Memo method will memorize the result till the props are same. ...
Read MoreAdding bootstrap to React.js project
There are multiple ways to add bootstrap in react project.Using bootstrap CDNInstalling bootstrap dependencyUsing react bootstrap packagesUsing bootstrap CDNThis is the simplest way to add bootstrap. Like other CDN, we can add bootstrap CDN in index.html of the react project.Below is one of the react CDN urlIf we need the JavaScript components of bootstrap then we should add the jquery, popper.js in the index.htmlWith this the complete index.html will look like − React App hello Adding bootstrap dependencynpm install bootstrap ...
Read MoreSelecting rows that are older than current date in MySQL?
Let’s say the current date is 2019-08-03. Now, we will see an example and create a table −mysql> create table DemoTable840(DueDate datetime); Query OK, 0 rows affected (0.66 sec)Insert some records in the table using insert command −mysql> insert into DemoTable840 values('2019-08-9'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable840 values('2019-07-5'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable840 values('2019-08-10'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable840 values('2019-07-13'); Query OK, 1 row affected (0.10 sec)Display all records from the table using select statement −mysql> select *from DemoTable840;This will produce the ...
Read MoreMySQL query to sum rows having repeated corresponding Id
To sum, you can use aggregate function SUM(). Let us first create a table −mysql> create table DemoTable850( Id int, Price int ); Query OK, 0 rows affected (0.54 sec)Insert some records in the table using insert command −mysql> insert into DemoTable850 values(1, 90); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable850 values(2, 100); Query OK, 1 row affected (0.55 sec) mysql> insert into DemoTable850 values(2, 50); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable850 values(1, 80); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable850 values(1, 60); Query OK, ...
Read MoreChange the curdate() (current date) format in MySQL
The current date format is ‘YYYY-mm-dd’. To change current date format, you can use date_format().Let us first display the current date −mysql> select curdate();This will produce the following output −+------------+ | curdate() | +------------+ | 2019-08-08 | +------------+ 1 row in set (0.00 sec)Following is the query to change curdate() (current date) format −mysql> select date_format(curdate(), '%m/%d/%Y');This will produce the following output −+------------------------------------+ | date_format(curdate(), '%m/%d/%Y') | +------------------------------------+ | 08/08/2019 | +------------------------------------+ 1 row in set (0.00 sec)Let us first create a table −mysql> create table DemoTable ...
Read MoreGet the sum of columns for duplicate records in MySQL
For this, use GROUP BY clause along with aggregate function SUM(). Let us first create a table −mysql> create table DemoTable( Name varchar(100), Score int ); Query OK, 0 rows affected (0.70 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('Adam', 50); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('Bob', 80); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('Adam', 70); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('Adam', 10); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('Carol', ...
Read MoreDisplay the sum of positive and negative values from a column in separate columns with MySQL
For this, you can use CASE statement. Let us first create a table −mysql> create table DemoTable( Id int, Value int ); Query OK, 0 rows affected (0.51 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(10, 100); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(10, -110); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(10, 200); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(10, -678); Query OK, 1 row affected (0.17 sec)Display all records from the table using select statement −mysql> ...
Read MoreMySQL query to insert row with date?
Let us first create a table −mysql> create table DemoTable( EmployeeId int NOT NULL AUTO_INCREMENT PRIMARY KEY, EmployeeName varchar(100), JoiningDate date ); Query OK, 0 rows affected (0.48 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(EmployeeName, JoiningDate) values('Chris', '2019-01-21'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable(EmployeeName, JoiningDate) values('Robert', '2016-12-01'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(EmployeeName, JoiningDate) values('Mike', '2015-03-12'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select *from DemoTable;This will produce the following output −+------------+--------------+-------------+ ...
Read MoreInserting data into a new column of an already existing table in MySQL?
Let us first create a table −mysql> create table DemoTable( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Name varchar(100) ); Query OK, 0 rows affected (0.47 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(Name) values('John'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable(Name) values('Bob'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable(Name) values('Adam'); Query OK, 1 row affected (0.28 sec)Display all records from the table using select statement −mysql> select *from DemoTable;This will produce the following output −+----+------+ | Id | Name | +----+------+ | 1 | ...
Read MoreWhat is "SELECT TRUE" in MySQL?
The statement SELECT TRUE returns 1 if a row match. Let us first create a table −mysql> create table DemoTable(Name varchar(100)); Query OK, 0 rows affected (0.54 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('Chris'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values('Robert'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values('David'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select *from DemoTable;This will produce the following output −+--------+ | Name | +--------+ | Chris | | Robert ...
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