MYSQLI INTERVIEW QUESTIONS Updated

MySQL is an open source Database Management System which is built, supported and distributed by MySQL AB (now acquired by Oracle)

Data Definition Language deals with database schemas and descriptions of how the data should reside in the database, therefore language statements like CREATE TABLE or ALTER TABLE belong to DDL.
DML deals with data manipulation, and therefore includes most common SQL statements such SELECT, INSERT and Update etc.
Data Control Language includes commands such as GRANT, and mostly concerns with rights, permissions and other controls of the database system.

RDBMS (relational database management system) applications store data in a tabular form.
. DBMS store data as files .However there are is tables in DBMS also, but there is no relation between the tables as in RDBMS.
.In DBMS, data is generally stored in either a hierarchical form or a navigational form.
.In RDBMS tables have an identifier called primary key and Data values will be stored in the form of tables. The relationships  between these data  values will be stored in the form of a table as well.  Every value stored in the relational database is accessible.
.RDBMS solution is required by large sets of data whereas small sets of data can be managed by DBMS.

<?php
$con = mysqli_connect("localhost","my_user","my_password","my_db");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
?>

<?php
// DB credentials.
define('DB_HOST','localhost');
define('DB_USER','my_user');
define('DB_PASS','my_password');
define('DB_NAME','my_db');
// Establish database connection.
try
{
$dbh = new PDO("mysql:host=".DB_HOST.";dbname=".DB_NAME,DB_USER, DB_PASS,array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'"));
}
catch (PDOException $e)
{
exit("Error: " . $e->getMessage());
}
?>

Join  are used to fetch data from one or more tables based on relation between column .
Eg-

SELECT tablename1.columnname, tablename1.columnname, tablename2.columnname
FROM tablename2
JOIN tablename1 ON tablename1.columnname=tablename2.columnname;

ORDER BY  used to sort the result in ascending or descending order. By default records are sort in ascending
Eg- SELECT column1, column2, …FROM tablename ORDER BY column1… ASC|DESC;
GROUP BY used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns.
Eg- SELECT columnname FROM tablename WHERE condition GROUP BY columnname