What is SQL? A Beginner's Definitive Guide

The internet has tons of data and information lying around. Every second, quintillion bytes of data are created. But where does this huge volume of information get stored? Well, the answer is databases. 

A database is a collection of data arranged in a systematic manner, stored and retrieved electronically from computer systems. It stores data in the form of tables with multiple rows and columns, each with several entries. 

Data professionals retrieve the data from these tables with the help of SQL or Structured Query Language. SQL is undoubtedly an essential language for handling databases. 

If you are new to this field, this article will familiarize you with SQL and its work. Let’s tread ahead and understand the topic in detail. This article will cover what SQL is, top SQL commands, the evolution of SQL, as well as the advantages and applications.

For a deep dive, consider the SQL from A to Z track. It contains seven interactive courses and boasts more than 40,000 previous and current students.

Ready for learn the basics right now? Let’s get started!

What is SQL?

SQL stands for Structured Query Language. It is a standardized programming language used to handle and perform several operations on relational databases. 

Back in 1986, the American National Standards Institute (ANSI) made SQL a standard language. Moreover, the International Organization for Standardization (ISO) has made SQL the database standard as well. 

SQL is a popular and extensively used language to extract data and organize it in relational databases. SQL queries are used to execute several tasks, such as retrieving, deleting, or updating data in databases. There are some traditional commands to accomplish these tasks, such as ‘Update,’ ‘Insert,’ ‘Delete,’ ‘Drop,’ ‘Create,’ and ‘Select.’

Furthermore, some of the most popular Relational Database Management Systems (RDBMS) that use SQL are:

• Microsoft SQL Server
• Oracle
• Access
• Sybase
• Ingres

Functions of SQL

There are various applications of SQL, including:

• Create, delete, update, or drop tables and databases
• Modify or access data in RDBMS
• Define data in databases.
• Use SQL modules and libraries with other languages

Now that you understand the basics of SQL, let’s move on to the different types of data used with SQL. 

SQL Data Types 

In SQL, you can use these data types:

• Numeric 
• Binary 
• Character String 
• Date and time 

Top SQL Commands

SQL has several statements or commands to make changes in the database. Here are the most frequently used SQL commands:

1. Create
2. Update
3. Alter
4. Explain
5. Truncate
6. Select
7. Drop
8. Grant
9. Like
10. Insert Into

Let’s dive into each command in detail, along with examples.

Create

The “Create” command is used to create a table, database, or view:

For Database

SQL uses the below statement to create a new database:

Syntax:

Create Database DatabaseName;

Example:

Create Database EmployeeDetail;

For Table

SQL uses the below statement to create a table.

Syntax:

CREATE TABLE TableName 
(
Column1 data type,
Column2 data type,
Column3 data type
);

Example:

CREATE TABLE Employee
(
CustomerID int,
CustomerName varchar(255),
PhoneNumber int,
Address varchar(255),
City varchar(255),
Country varchar(255)
);

The above lines of code create a table named ‘Employee’, with CustomerID, CustomerName, PhoneNumber, Address, City, and Country, as attributes or columns.

For View

To create a view, use the syntax below: 

Syntax:

CREATE VIEW OR REPLACE ViewName AS
SELECT Column1, Column2, ..., ColumnN
FROM TableName
WHERE Condition;

Example:

CREATE VIEW OR REPLACE DLIEmployees AS
SELECT CustomerName, PhoneNumber
FROM Customers
WHERE City = "DELHI";

This creates a view with two columns, CustomerName and PhoneNumber, of customers from the ‘Customers’ table, whose city is Delhi. 

Update

If you wish to make modifications to the already existing data in your table, use the Update statement. 

Syntax:

UPDATE TableName
SET Column1 = Value1, Column2 = Value2, ...
WHERE Condition;

Example:

UPDATE Employee
SET EmployeeName = 'Rachel', City= 'Los Angeles'
WHERE EmployeeID = 5;

This statement updates the details of the Employee, whose EmployeeID is 5. 

Alter

You can use the Alter statement to add, modify, or delete columns of a table. 

Syntax:

Add column:

ALTER TABLE TableName 

ADD ColumnName Data Type;

Drop Column:

ALTER TABLE TableName 

DROP COLUMN ColumnName;

Modify Column Name:

ALTER TABLE TableName 

ALTER COLUMN ColumnName Data Type;

Example:

ADD Column Address:​

ALTER TABLE Employee 

ADD Address varchar(255);

It adds a column named ‘Address’ to the ‘Employee’ table.  

DROP Column Address:

ALTER TABLE Employee 

DROP COLUMN Address ;

It drops a column named ‘Address’ from the ‘Employee’ table.  

Now, add a column JoiningDate to your table and set the data type as ‘year’, as shown below:

ALTER TABLE JoiningDate 

ADD JoiningDate date;​

ALTER TABLE JoiningDate 

ALTER JoiningDate year;

To fetch information from the table, we use the Explain statement. Explain

Syntax:

EXPLAIN ANALYZE
SELECT * FROM Table1 JOIN Table2 ON (Table1.Column1 = Table2.Column2);

Example:

EXPLAIN ANALYZE
SELECT * FROM Employee1 JOIN Orders ON (Customers.CustomerID = Orders.CustomerID);

The result contains tuples or rows from the tables ‘Employee1’ and ‘Orders,’ whose  CustomerID is the same. 

Truncate

To delete complete data from a table, use truncate.

Syntax:

TRUNCATE TABLE TableName;

Example:

TRUNCATE Table Customers;

This statement deletes all data stored in the ‘Customers’ table. 

Select

To retrieve a particular set of information from the table, use Select.

Syntax:

SELECT Column1, Column2, ...ColumN 

FROM TableName;

(*) - to select all the data from a particular table

SELECT * FROM table_name;

Example:

SELECT EmployeeID, EmployeeName 

FROM Customers;

It returns EmployeeID and EmployeeName columns from the ‘Customers’ table.   

(*) - to select all the data from a particular table

SELECT * FROM Employee;

This returns the entire data of the ‘Employee’ table. 

Drop

To completely delete the entire database at once, use the Drop statement.

Syntax:

DROP DATABASE DatabaseName;

Example:

DROP TABLE Employee;

This drops the ‘Employee’ table. 

Grant

The Grant statement is used to access the database to the users.

Syntax:

GRANT PName
ON Object1
TO [WITH GRANT OPTION];

Example:

GRANT SELECT ON Customers TO admin;

Like

The ‘Like’ operation is used with the ‘Where’ clause. If you wish to find a particular pattern in the table, use the ‘Where’ clause. 

Syntax:

SELECT ColumnName(s)
FROM TableName
WHERE ColumnName LIKE pattern;

Example:

SELECT * FROM Employee
WHERE EmployeeName LIKE 'A%';

Here, ‘%’ matches with 0 or more characters.

Insert Into

To insert new data into the table, use an Insert Into statement. 

Syntax:

INSERT INTO TableName (Column1, Column2, Column3, ...,Column100)
VALUES (value1, value2, value3, ...);

In this case, mentioning the column names is not required. You can match the order of values with the column data types, as shown below:

INSERT INTO TableName
VALUES (Value1, Value2, Value3, ...);

Example:

INSERT INTO Employee(EmployeeID, EmployeeName, PhoneNumber, Address, City)
VALUES ('15', 'Ana', '0000000000', 'House No 56, 5th Avenue', 'London');​

INSERT INTO Employee
VALUES ('10', 'Ross','1111111111', 'Carlton Inn, 45', 'New York');

The above statements insert the data of an employee into the ‘Employee’ table. 

SQL History

Raymond Boyce and Donald Chamberlin, IBM’s researchers first developed the Structured Query Language (SQL) in the 1970s. Earlier, SQL was known as SEQUEL, which was created in 1970 after the publication of Edgar Frank Todd's paper, "A Relational Model of Data for Large Shared Data Banks."

In this paper, Todd represented that all the data in a database can be represented in the form of relations. Author Malcolm Coxall in his book "Oracle Quick Guides “ has written that SQL was originally designed to manipulate data stored in IBM’s relational management system, called “System R”. 

Later in 1979, a company called Relational Software, now known as Oracle, released the commercial version of their own SQL language, called Oracle V2, and made it public. After that, American National Standards Institute (ANSI) and the International Standards Organization have considered SQL a standard language in relational database communication. 

Why SQL Was Born

Data storage has been a major challenge for professionals throughout history.

The major obstacles that hampered the previous form of data storage were:

• Security issues
• Dependency of data
• Redundant data
• Slow speed
• Scalability

Security Issues

When it comes to sharing data with a wide variety of users, security is always a threat. Basic data sharing sheets or documents do not provide high-tech security options. General security features such as password protection, locking specific parts of the documents, etc., are not enough to protect the data from external threats.

Dependency of Data

There are plenty of files and records in a file system that follow a particular format. If any modification is done to a single file or record, it is mandatory to update the rest of the records as well. After that, it is mandatory to make the changes to the entire system.

Hence, it’s clearly a time-consuming and meticulous task, creating a big drawback of the file system. 

Redundant Data

In a file system, there is no mechanism to track duplicate files. In a system, the same files can be stored at different locations, leading to redundancy. 

Data redundancy occupies unnecessary storage in your system and poses security threats as well. 

Slow Speed

A file system requires more programming and queries to fetch new reports or files, and it consumes plenty of time and becomes laborious to retrieve solutions quickly. This again forms a big impediment to the seamless management of data in the file system. 

Scalability

You need to opt for a solution that fulfills your current needs. But, the needs of businesses are subjected to change with time. To adapt to this change, you must keep a data storage system that provides scalability. 

The file system wasn’t scalable, so it lagged behind. 

Advantages of SQL

Here are some of the advantages of SQL:

• Easy to learn: SQL is a highly user-friendly language for beginners to learn.
• Easy syntax: Every SQL query is formulated in a structured way by the developers. To successfully execute these commands, you have to follow the standard ways to write each command/statement, which offers easy syntax.
• Interactive language: The primary objective of the SQL language is to retrieve results from a database. You can easily communicate with the help of this language with the tables to fetch the desired data.
• Portable: By maintaining the same environment setup of the system, you can execute the same queries on different systems. If the environment is different, then the execution won’t be possible.
• Create several views: View is a virtual table created with the help of SQL. It is used for temporary purposes to fulfill a requirement.

Related: 10 Best Online SQL Courses

Moving further, you may wonder about the real-time usage of SQL — which brings us to our next section.

Applications and Uses of SQL

In this data-driven world, SQL is being used widely, since managing massive databases has become the primary concern. It is a primary and standard language to query relational databases, like MySQL, Oracle, etc. 

The following are some applications and uses of SQL:

• We can use SQL as a Data Definition Language (DDL), meaning that we can create a database, characterize its structure, use it, and delete it afterwards. Also, we can call it a Data Control Language (DCL) which enables us to decide the grant and revoke permissions to our database. 
• SQL can also be used as a Data Manipulation Language (DML), meaning that we can manage existing databases and perform various operations on data stored in a database. 
• We can also use SQL as a client or server language to connect the front-end and back-end of applications. 

Industries That Use SQL

SQL is used in a plethora of industries across the globe, as it ensures efficient storage of data. 

Here are just a few examples of industries that employ SQL: 

Education

In various educational institutions, such as schools, colleges, or universities, there is a requirement to retrieve or save the staff data. SQL helps maintain a record of information like exam details, staff details, student details, courses, syllabus, attendance, fee details, etc. 

Finance

It’s challenging to manage assets, shares, and money. With SQL, the finance sector can easily handle and manage the vast data it produces.

Retail

There are large volumes of data in retail to be managed, and SQL not only manages this data, but also provides security. On a large scale, retail businesses are opting for SQL to handle their data as well as for real-time analysis.

Healthcare

The healthcare sector requires a reliable management system to maintain the data of their staff, patients, pharmacy, to name a few. SQL helps this industry to maintain all these records along with other vital benefits. The easy management of databases from SQL has helped the healthcare industry to work seamlessly. 

Conclusion

In a nutshell, SQL is a standardized language implemented to manage relational databases and handle several operations on them, such as adding, deleting, updating, inserting, and modifying data in the databases. It is a boon for organizations to help them handle large volumes of information with ease. 

SQL resolves the hurdles encountered in managing data such as redundancy, security, data dependency, and much more. Major industries are implementing SQL in their businesses. 

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