Structured
Query Language (SQL) is a specialized programming language for
managing relational database data. It allows users to store, manipulate, and
retrieve data efficiently in databases like MySQL, SQL
Server, Oracle, and more.
In this
article, we will learn about what is SQL? and check its characteristics, rules,
uses, commands, etc.
What is
SQL?
SQL stands
for Structured Query Language. SQL is a computer language used to interact with
relational database systems. SQL is a tool for organizing, managing, and
retrieving archived data from a computer database.
When data
needs to be retrieved from a database, SQL is used to make the request. The
DBMS processes the SQL query retrieves the requested data and returns it to us.
Rather, SQL statements describe how a collection of data should be organized or
what data should be extracted or added to the database.
In common
usage, SQL encompasses DDL and DML commands
for CREATE, UPDATE, MODIFY, or other
operations on database structure.
SQL
History
- SQL was invented in 1970s and
was first commercially distributed by Oracle.
- The original name was given by
IBM as Structured English Query Language, abbreviated by the acronym
SEQUEL.
Components
of a SQL System
Some of the
Key components of a SQL System are:
Databases
Databases are structured collections of data
organized into tables, rows, and columns. They serve as repositories for
storing information efficiently and provide a way to manage and access data.
Tables
Tables are the fundamental building blocks
of a database, consisting of rows (records) and columns (attributes or fields).
They ensure data integrity and consistency by defining the structure and
relationships of the stored information.
Queries
Queries are
SQL commands used to interact with databases. They enable users to retrieve,
update, insert, or delete data from tables, allowing for efficient data
manipulation and retrieval.
Constraints
Constraints are rules applied to tables to
maintain data integrity. They define conditions that data must meet to be
stored in the database, ensuring accuracy and consistency.
Stored
Procedures
Stored
Procedures are
pre-compiled SQL statements stored in the database. They can accept parameters,
execute complex operations, and return results, enhancing efficiency,
reusability, and security in database management.
Transactions
Transactions are groups of SQL statements that are
executed as a single unit of work. They ensure data consistency and integrity
by allowing for the rollback of changes if any part of the transaction fails.
Some other
important components include:
- Data Types
- Indexes
- Views
- Security and Permissions
- Joins
What are
the characteristics of SQL?
- SQL may be utilized by quite a
number of users, which include people with very little programming
experience.
- SQL is a non-procedural
language.
- We can without difficulty create
and replace databases in SQL. It isn’t a time-consuming process.
- SQL is primarily based totally
on ANSI standards.
- SQL does now no longer have a
continuation individual.
- SQL is entered into the SQL
buffer on one or more lines.
- SQL makes use of a termination
individual to execute instructions immediately. It makes use of features
to carry out a few formatting.
- It uses functions to perform
some formatting.
How SQL
Works?
A server
machine is used in the implementation of the structured query language (SQL),
processing database queries and returning results. The following are some of
the software elements that the SQL process goes through.
Parser
The parser
begins by replacing some of the words in the SQL statement with unique symbols,
a process known as tokenization. The statement is then examined for the
following:
Correctness
The parser
checks to see if the SQL statement complies with the rules, or SQL semantics,
that guarantee the query statement’s accuracy. The parser, for instance, looks
to see if the SQL command ends with a semicolon. The parser returns an error if
the semi-colon is absent.
Authorization
The parser
additionally confirms that the user executing the query has the required
permissions to alter the relevant data.
Relational
Engine
The
relational engine, also known as the query processor, develops a strategy for
efficiently retrieving, writing, or updating relevant data. For instance, it
looks for queries that are similar to others, uses earlier data manipulation
techniques, or develops a new one. Byte code, an intermediate-level
representation of the SQL statement, is used to write the plan. To efficiently
perform database searches and modifications, relational databases use byte
code.
Storage
Engine
The software
element that interprets the byte code and executes the intended SQL statement
is known as the storage engine, also known as the database engine. The data in
the database files on the physical disc storage is read and stored. The storage
engine delivers the outcome to the requesting application after completion.
SQL Rules
The rules
for writing SQL queries are given below:
- A ‘;’ is used to end SQL
statements.
- Statements may be split across
lines, but keywords may not.
- Identifiers, operator names, and
literals are separated by one or more spaces or other delimiters.
- A comma (,) separates parameters
without a clause.
- A space separates a clause.
- Reserved words cannot be used as
identifiers unless enclosed with double quotes.
- Identifiers can contain up to 30
characters.
- Identifiers must start with an
alphabetic character.
- Characters and date literals
must be enclosed within single quotes.
- Numeric literals can be
represented by simple values.
- Comments may be enclosed between
/* and */ symbols and maybe multi-line.
What are
SQL commands?
Developers
use structured query language (SQL) commands, which are specific keywords or
SQL statements, to work with data stored in relational databases. The following
are categories for SQL commands.
1. Data
Definition Language
SQL commands
used to create the database structure are known as data definition language
(DDL). Based on the needs of the business, database engineers create and modify
database objects using DDL. The CREATE command, for instance, is used by the
database engineer to create database objects like tables, views, and indexes.
Command |
Description |
CREATE |
Creates a new table, a view of a table, or other
object in the database. |
ALTER |
Modifies an existing database object, such as a
table |
DROP |
Deletes an entire table, a view of a table, or
other objects in the database |
2. Data
Manipulation Language
A relational
database can be updated with new data using data manipulation language (DML)
statements. The INSERT command, for instance, is used by an application to add
a new record to the database.
Command |
Description |
SELECT |
Retrieves certain records from one or more tables. |
INSERT |
Creates a record. |
UPDATE |
Modifies records. |
DELETE |
Deletes records. |
3. Data
Query Language
Data
retrieval instructions are written in the data query language (DQL), which is
used to access relational databases. The SELECT command is used by software
programs to filter and return particular results from a SQL table.
4. Data
Control language
Data control
language (DCL) is a programming language used by database administrators to
control or grant other users access to databases. For instance, they can allow
specific applications to manipulate one or more tables by using the GRANT
command.
Command |
Description |
GRANT |
Gives a privilege to the user. |
REVOKE |
Takes back privileges granted by the user. |
5.
Transaction Control Language
To
automatically update databases, the relational engine uses transaction control
language (TCL). For instance, the database can reverse a mistaken transaction
using the ROLLBACK command.
Uses of
SQL
SQL is used
for interacting with databases. These interactions include:
- Data definition: It is used to define the
structure and organization of the stored data and the relationships
among the stored data items.
- Data retrieval: SQL can also be used for
data retrieval.
- Data manipulation: If the user wants to add new
data, remove data, or modifying in existing data then SQL provides this
facility also.
- Access control: SQL can be used to
restrict a user’s ability to retrieve, add, and modify data, protecting
stored data against unauthorized access.
- Data sharing: SQL is used to coordinate data
sharing by concurrent users, ensuring that changes made by one user do not
inadvertently wipe out changes made at nearly the same time by another
user.
SQL also
differs from other computer languages because it describes what the
user wants the computer to do rather than how the computer should do
it. (In more technical terms, SQL is a declarative or descriptive language
rather than a procedural one.)
SQL contains
no IF statement for testing conditions, and no GOTO, DO, or
FOR statements for program flow control. Rather, SQL statements describe
how a collection of data is to be organized, or what data is to be retrieved or
added to the database. The sequence of steps to do those tasks is left for the
DBMS to determine.
Why SQL?
- SQL is an interactive question
language. Users type SQL instructions into an interactive SQL
software to retrieve facts and show them on the screen, presenting a
convenient, easy-to-use device for ad hoc database queries.
- SQL is a database programming
language. Programmers embed SQL instructions into their utility
packages to access the facts in a database. Both user-written packages and
database software packages (consisting of document writers and facts
access tools) use this approach for database access.
- SQL is a client/server
language. Personal computer programs use SQL to communicate over a
network with database servers that save shared facts. This client/server
architecture is utilized by many famous enterprise-class applications.
- SQL is Internet facts
access language. Internet net servers that interact with company
facts and Internet utility servers all use SQL as a widespread language
for getting access to company databases, frequently through embedding SQL
databases get entry to inside famous scripting languages like PHP or Perl.
- SQL is a distributed
database language. Distributed database control structures use SQL to
assist distribute facts throughout many linked pc structures. The DBMS
software program on every gadget makes use of SQL to speak with the
opposite structures, sending requests for facts to get entry to.
- SQL is a database gateway
language. In a pc community with a mixture of various DBMS products,
SQL is frequently utilized in a gateway that lets one logo of DBMS
speak with every other logo. SQL has for this reason emerged as a useful,
effective device for linking people, pc packages, and pc structures to the
facts saved in a relational database.
SQL
Injection
A
cyberattack known as SQL injection involves tricking the database with SQL
queries. To retrieve, alter, or corrupt data in a SQL database, hackers use SQL
injection. To execute a SQL injection attack, for instance, they might enter a
SQL query in place of a person’s name in a submission form.
What is
SQL Server?
Microsoft’s
relational database management system, which uses SQL to manipulate data, is
formally known as SQL Server. There are various editions of the MS SQL Server,
and each is tailored for particular workloads and requirements.
Finally, SQL
is not a particularly structured language, especially when compared with highly
structured languages such as C, Pascal, or Java. Instead, SQL statements
resemble English sentences, complete with “noise words” that don’t add to the
meaning of the statement but make it read more naturally. SQL has quite a few
inconsistencies and also some special rules to prevent you from constructing
SQL statements that look perfectly legal but that don’t make sense.
Despite the
inaccuracy of its name, SQL has emerged as the standard language for using
relational databases. SQL is
both a powerful language and one that is relatively easy to learn. So, SQL is a
database management language. The database administrator is answerable for
handling a minicomputer or mainframe database and makes use of SQL to outline
the database shape and manipulate get entry to the saved data.
Conclusion
SQL(Structured
Query Language) is a programming language designed for managing and
manipulating data stored in relational databases. It is used for interacting
with DBMS like MySQL, SQL Server, Oracle, and PostgreSQL.
In this
article we have covered about SQL and understood it’s characteristics, rules to
write SQL queries, commands, uses and many important concepts. We also covered
the SQL injection and how it can be harmful for database security. After
completing this guide, you will be equipped with all necessary information
about SQL.
What is
SQL – Frequently Asked Questions
What is
SQL and why is it used?
SQL
(Structured Query Language) is a specialized programming language designed for
managing and interacting with relational databases. It is widely used across
industries for efficient data storage, fast query processing, and robust
security features.
What is
an SQL example?
An
example of a simple SQL query:
SELECT * FROM customers WHERE customer_name LIKE ‘J%’ ORDER
BY customer_id DESC LIMIT 10;
This
query retrieves the top 10 customers whose names start with ‘J’, ordered in
descending order by their customer ID
Is SQL
used in Excel?
No, SQL
is not directly used in Microsoft Excel. SQL is a specialized language for
managing and interacting with relational databases, while Excel is a
spreadsheet application with its own set of functions and formulas for data
manipulation.
Is SQL a
coding language?
Yes, SQL
(Structured Query Language) is considered a coding language designed for
managing and interacting with relational databases.
Where can
I use SQL?
You can
use SQL in various industries and applications, including finance, healthcare,
data science, marketing, web development, and cybersecurity, to manage,
analyze, and manipulate data efficiently.
Is SQL
for free?
Yes, you
can learn and use SQL for free through various online resources and platforms.
Some free SQL software are, MySQL, PostgreSQL, Microsoft SQL, SQL Server, etc.
Let's
Deep dive under some of the SQL Database servers :
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