How do you enable error reporting in PHP?

 PHP allows us to choose whether or not to display errors to users. There are three ways to enable or disable error reporting in PHP:

Method 1: You can turn the display error parameter in the php.ini file on or off. When it’s on, errors are shown; when it’s off, there are no errors shown or reported. To do this, locate the display error parameter in the php.ini file, then set its value to “on.” Restart the web server's various services. The PHP script's errors will now be visible to end users. Set the display error parameter to “off” to stop reporting errors. The off argument indicates that users won't see any errors.

Method 2: Using the mini set() function is the second way to enable or stop error reporting. The ability to modify the configuration options in the php.ini file is a built-in feature of the PHP programming language. It requires two inputs: the name of the setting you want to change and the value you want to assign.

Method 3: You can also utilize the error reporting() function, a native PHP function, to enable error reporting. This function controls which PHP faults are reported and sets the error reporting directive during runtime. Given that PHP has multiple error levels, this method also aids in setting the various levels for the runtime (duration) of your script. This function accepts parameters for error names like E ERROR, E WARNING, E PARSE, etc., allowing these errors to be reported.

What is the difference between MySQL, MySQLi and PDO?

To understand the difference between MySQL, MySQLi, and PDO, we must know about each one of them individually.

These are nothing but the APIs of PHP that is used to access the MySQL databases and tables. The developers can choose either one of them for their project, however, it must be known that MySQLi cannot be used with PHP 7 and its newer versions. However, developers can use MySQLi with PHP 5, which is now deprecated.

Let’s have some more information about each of them:

• MySQL: This was the main extension that was designed to help PHP applications send and receive data from MySQL database. However, use of MySQL has been deprecated and removed as of PHP 7 and its newer versions. This is why it is not recommended for new projects, and that’s the reason why MySQLi and PDO extensions are used more nowadays.
• MySQLi: The ‘i’ in MySQLi stands for Improved. Therefore, this is also known as the improved version of MySQL. It has many new features that will be covered later in the article.
• PDO – PHP Data Objects: The main advantage of using PDO is that it supports, and provides a uniform method of access to 11 different databases.
  

What is a foreign key? Write a query to implement the same in MySQL.

 A foreign key is used to connect two tables. A FOREIGN KEY is a field (or assortment of it) in one table that alludes to the PRIMARY KEY in another table. The FOREIGN KEY requirement is utilised to forestall activities that would crush joins between tables.

To assign a foreign key, it is important to mention it while creating the table. It can be assigned by invoking the FOREIGN KEY query. Something like this:

FOREIGN KEY (Any_ID) REFERENCES Table_to_reference(Any_ID)

Write a query for a column addition in MySQL

 For this, an ALTER TABLE query is required. Once invoked, simply mention the column and its definition. Something like this:

ALTER TABLE cars

ADD COLUMN engine VARCHAR(80) AFTER colour;

What are the tables in MySQL? Explain the types.

 This is a must-know MySQL interview question. Let’s see the answer-

MySQL stores everything in logical tables. Tables can be thought of as the core storage structure of MySQL. And hence tables are also known as storage engines. Here are the storage engines provided by MySQL:

· MyISAM – MyISAM is the default storage engine for MySQL. It extends the former ISAM storage engine. MyISAM offers big storage, up to 256TB! The tables can also be compressed to get extra storage. MyISAM tables are not transaction-safe. 

· MERGE – A MERGE table is a virtual table that consolidates different MyISAM tables that have a comparable structure to one table. MERGE tables use the indexes of the base tables, as they do not have indexes of their own.

How To Delete Duplicate Rows in MySQL

 Summary: in this tutorial, you will learn various ways to delete duplicate rows in MySQL.

In the previous tutorial, we have shown you how to find duplicate values in a table. Once the duplicates rows are identified, you may want to delete them to clean up your data.

Prepare sample data

The following script creates table contacts and inserts sample data into the contacts table for the demonstration.

DROP TABLE IF EXISTS contacts;

CREATE TABLE contacts (
    id INT PRIMARY KEY AUTO_INCREMENT,
    first_name VARCHAR(50) NOT NULL,
    last_name VARCHAR(50) NOT NULL, 
    email VARCHAR(255) NOT NULL
);

INSERT INTO contacts (first_name,last_name,email) 
VALUES ('Carine ','Schmitt','carine.schmitt@verizon.net'),
       ('Jean','King','jean.king@me.com'),
       ('Peter','Ferguson','peter.ferguson@google.com'),
       ('Janine ','Labrune','janine.labrune@aol.com'),
       ('Jonas ','Bergulfsen','jonas.bergulfsen@mac.com'),
       ('Janine ','Labrune','janine.labrune@aol.com'),
       ('Susan','Nelson','susan.nelson@comcast.net'),
       ('Zbyszek ','Piestrzeniewicz','zbyszek.piestrzeniewicz@att.net'),
       ('Roland','Keitel','roland.keitel@yahoo.com'),
       ('Julie','Murphy','julie.murphy@yahoo.com'),
       ('Kwai','Lee','kwai.lee@google.com'),
       ('Jean','King','jean.king@me.com'),
       ('Susan','Nelson','susan.nelson@comcast.net'),
       ('Roland','Keitel','roland.keitel@yahoo.com');
Code language: SQL (Structured Query Language) (sql)

Note that you can execute this script to recreate test data after you execute a DELETE statement.

How To Find Duplicate Values in MySQL

 Summary: in this tutorial, you will learn how to find duplicate values of one or more columns in MySQL.

Data duplication happens because of many reasons. Finding duplicate values is one of the important tasks that you must deal with when working with the databases.

Setting up a sample table

First, create a table named contacts with four columns: id, first_name, last_name, and email.

CREATE TABLE contacts (
    id INT PRIMARY KEY AUTO_INCREMENT,
    first_name VARCHAR(50) NOT NULL,
    last_name VARCHAR(50) NOT NULL,
    email VARCHAR(255) NOT NULL
);
Code language: SQL (Structured Query Language) (sql)

Second, inserts rows into the contacts table:

INSERT INTO contacts (first_name,last_name,email) 
VALUES ('Carine ','Schmitt','carine.schmitt@verizon.net'),
       ('Jean','King','jean.king@me.com'),
       ('Peter','Ferguson','peter.ferguson@google.com'),
       ('Janine ','Labrune','janine.labrune@aol.com'),
       ('Jonas ','Bergulfsen','jonas.bergulfsen@mac.com'),
       ('Janine ','Labrune','janine.labrune@aol.com'),
       ('Susan','Nelson','susan.nelson@comcast.net'),
       ('Zbyszek ','Piestrzeniewicz','zbyszek.piestrzeniewicz@att.net'),
       ('Roland','Keitel','roland.keitel@yahoo.com'),
       ('Julie','Murphy','julie.murphy@yahoo.com'),
       ('Kwai','Lee','kwai.lee@google.com'),
       ('Jean','King','jean.king@me.com'),
       ('Susan','Nelson','susan.nelson@comcast.net'),
       ('Roland','Keitel','roland.keitel@yahoo.com');
Code language: SQL (Structured Query Language) (sql)

What does a MySQL database contain?

 A MySQL database contains one or more tables, each of which contains records or rows. Within these rows are various columns or fields that contain the data itself.

What does SQL in MySQL stand for?

 The SQL in MySQL stands for Structured Query Language. This language is also used in other databases such as Oracle and Microsoft SQL Server.  One can use commands such as the following to send requests from a database:

SELECT title FROM publications WHERE author = ' J. K. Rowling’;

Note that SQL is not case sensitive. However, it is a good practice to write

the SQL keywords in CAPS and other names and variables in a small case.

What do you mean by ‘databases’?

 A database is a structured collection of data stored in a computer system and organized in a way to be quickly searched. With databases, information can be rapidly retrieved.

What are some of the advantages of using MySQL?

 

• Flexibility: MySQL runs on all operating systems
• Power: MySQL focuses on performance
• Enterprise-Level SQL Features: MySQL had for some time been lacking in advanced features such as subqueries, views, and stored procedures.
• Full-Text Indexing and Searching
• Query Caching: This helps enhance the speed of MySQL greatly
• Replication: One MySQL server can be duplicated on another, providing numerous advantages
• Configuration and Security

What is MySQL?

 MySQL is a database management system for web servers. It can grow with the website as it is highly scalable. Most of the websites today are powered by MySQL.

The System Tablespace

 The system tablespace is the storage area for the InnoDB data dictionary, the doublewrite buffer, the change buffer, and undo logs. It may also contain table and index data if tables are created in the system tablespace rather than file-per-table or general tablespaces.

The system tablespace can have one or more data files. By default, a single system tablespace data file, named ibdata1, is created in the data directory. The size and number of system tablespace data files is defined by the innodb_data_file_path startup option. For configuration information, see System Tablespace Data File Configuration.

Additional information about the system tablespace is provided under the following topics in the section:

• Resizing the System Tablespace

• Using Raw Disk Partitions for the System Tablespace

Resizing the System Tablespace

This section describes how to increase or decrease the size of the system tablespace.

Increasing the Size of the System Tablespace

The easiest way to increase the size of the system tablespace is to configure it to be auto-extending. To do so, specify the autoextend attribute for the last data file in the innodb_data_file_path setting, and restart the server. For example:

SOLID Principles in PHP

This post is to provide an easy to understand idea about the implementation of one of the most “talked about” principles of Object Oriented Programming - SOLID principles. As a programmer, there might come a time when we are so consumed in finishing the task at hand that we forget the world around us. And in the very same world, somewhere lost are the programming principles that we read about and planned to use next time. So let’s try to look at the SOLID principles in one of the simplest way possible so that we can practice them while coding.

So let’s dig in to the SOLID principles at a glance.

1. Single Responsibility: A Class should be responsible for a single task.
2. Open-Close Principle: A Class should be open to extension and close to modification.
3. Liskov Substitution: A derived Class can be substituted at places where base Class is used.
4. Interface Segregation: Don’t make FAT Interfaces. i.e. Classes don’t have to override extra agreements that are not needed for that Class simply because it is there in interface.
5. Dependency Inversion: Depend on abstractions, not on concretions. Not only high level Classes but low level Classes also depend on the abstractions in order to decouple the code.

ENUM and SET Constraints

 ENUM and SET columns provide an efficient way to define columns that can contain only a given set of values. See Section 11.3.5, “The ENUM Type”, and Section 11.3.6, “The SET Type”.

Unless strict mode is disabled (not recommended, but see Section 5.1.11, “Server SQL Modes”), the definition of a ENUM or SET column acts as a constraint on values entered into the column. An error occurs for values that do not satisfy these conditions:

• An ENUM value must be one of those listed in the column definition, or the internal numeric equivalent thereof. The value cannot be the error value (that is, 0 or the empty string). For a column defined as ENUM('a','b','c'), values such as '', 'd', or 'ax' are invalid and are rejected.

• A SET value must be the empty string or a value consisting only of the values listed in the column definition separated by commas. For a column defined as SET('a','b','c'), values such as 'd' or 'a,b,c,d' are invalid and are rejected.

Errors for invalid values can be suppressed in strict mode if you use INSERT IGNORE or UPDATE IGNORE. In this case, a warning is generated rather than an error. For ENUM, the value is inserted as the error member (0). For SET, the value is inserted as given except that any invalid substrings are deleted. For example, 'a,x,b,y' results in a value of 'a,b'.

The ENUM Type

 An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation time.

See Section 11.3.1, “String Data Type Syntax” for ENUM type syntax and length limits.

The ENUM type has these advantages:

• Compact data storage in situations where a column has a limited set of possible values. The strings you specify as input values are automatically encoded as numbers. See Section 11.7, “Data Type Storage Requirements” for storage requirements for the ENUM type.

• Readable queries and output. The numbers are translated back to the corresponding strings in query results.

and these potential issues to consider:

• If you make enumeration values that look like numbers, it is easy to mix up the literal values with their internal index numbers, as explained in Enumeration Limitations.

• Using ENUM columns in ORDER BY clauses requires extra care, as explained in Enumeration Sorting.

• Creating and Using ENUM Columns

• Index Values for Enumeration Literals

• Handling of Enumeration Literals

• Empty or NULL Enumeration Values

• Enumeration Sorting

• Enumeration Limitations
  
  

Comparison of B-Tree and Hash Indexes

 Understanding the B-tree and hash data structures can help predict how different queries perform on different storage engines that use these data structures in their indexes, particularly for the MEMORY storage engine that lets you choose B-tree or hash indexes.

• B-Tree Index Characteristics

• Hash Index Characteristics

B-Tree Index Characteristics

A B-tree index can be used for column comparisons in expressions that use the =, >, >=, <, <=, or BETWEEN operators. The index also can be used for LIKE comparisons if the argument to LIKE is a constant string that does not start with a wildcard character. For example, the following SELECT statements use indexes:

SELECT * FROM tbl_name WHERE key_col LIKE 'Patrick%';
SELECT * FROM tbl_name WHERE key_col LIKE 'Pat%_ck%';

In the first statement, only rows with 'Patrick' <= key_col < 'Patricl' are considered. In the second statement, only rows with 'Pat' <= key_col < 'Pau' are considered.

The following SELECT statements do not use indexes:

SELECT * FROM tbl_name WHERE key_col LIKE '%Patrick%';
SELECT * FROM tbl_name WHERE key_col LIKE other_col;

In the first statement, the LIKE value begins with a wildcard character. In the second statement, the LIKE value is not a constant.

If you use ... LIKE '%string%' and string is longer than three characters, MySQL uses the Turbo Boyer-Moore algorithm to initialize the pattern for the string and then uses this pattern to perform the search more quickly.