What is SQL ? Full Form is Structured Query Language

Introduction to SQL

The term Structured Query Language usually goes by the abbreviation SQL. This potent tool controls and works with relational databases. SQL is so entrenched as the low-level language of database management that most users are blissfully unaware of its presence. You fire up Access or FileMaker, and they do it for you using a kind of magic. The same—except in more pronounced fashion—applies to web databases. When you work with a database on the internet, even an encrypted one running on a low-end server, the odds are that SQL is the management language doing the dirty work. In fact, a web database using anything other than SQL as its low-level management language would be like a society of people who, instead of using English, communicated in something like Toki Pona.

History and Evolution of SQL

Early Developments

The programming language known as the Standard Query Language (SQL) serves a singular, well-defined purpose: It manages and modifies the content of relational databases. You can use many different programming languages to interact with a database, but SQL is especially designed and suited for working with databases based on the relational model. Thus, SQL became the dominant language for database manipulation.

IBM's Contribution

Invented in the early 1970s by IBM (and then called SEQUEL), it was first described in a research paper in 1974. Then, in 1979, an SQL-based database called SQL/DS was introduced for use with IBM mainframe computers.

The Role of SQL in Modern Data Management

Simplicity and Efficiency

In the contemporary era, characterized by an abundance of data, SQL is a prominent figure in the realms of data administration and analytics. There are several bases on which to relevantly endorse SQL. To begin with, SQL is an exceedingly simple language for data manipulation. To insert, update, or delete records is an easy task with this language. Its syntax seems to even verge on the intuitive.

Data Retrieval

When we move on to the matter of data retrieval, SQL presents us with a formidable option—one that seems to be hard to better. If you give it a large quantity of data and ask it to find a specific piece of information, SQL will go right ahead and find it for you with good speed and even better accuracy. And you won't find a dataset that SQL can't handle.

Basic SQL Commands

SELECT Statement

Understanding the SQL syntax is essential for writing effective queries. SQL comprises several basic elements, and among them, the SELECT statement is the most crucial and most frequently used. You can use the SELECT statement to pull out one value or many values. 

The basic form of the SELECT statement is "SELECT column1, column2 FROM table_name WHERE condition."

INSERT Statement

After the SELECT statement comes the INSERT statement, which you use when you want to add new data to your tables. 

 basic form of the INSERT statement is "INSERT INTO table_name (column1, column2) VALUES (value1, value2)."

UPDATE Statement

If you want to replace existing data with new data, you use the UPDATE statement.

 The basic form of the UPDATE statement is "UPDATE table_name SET column1 = value1 WHERE condition."

DELETE Statement

If you want to get rid of unwanted data, you use the DELETE statement.

The basic form of the DELETE statement is "DELETE FROM table_name WHERE condition."

Advanced SQL Concepts

Joins

As your SQL skills increase, you will start to learn advanced concepts that can greatly enhance the power of your data manipulations. The first of these concepts is the join, which is the combining of rows from two or more tables based on a related column. The types of joins we will cover are:

- INNER JOIN: Returns records that have matching values in both tables.

- LEFT JOIN: Returns all records from the left table and the matched records from the right table.

- RIGHT JOIN: Returns all records from the right table and the matched records from the left table.

- FULL JOIN: Returns all records when there is a match in either table.

 Although the syntax for SQL joins can be a little more complex than for the commands we have covered so far, it is still pretty straightforward and not something to be unduly intimidated by.

 

Subqueries

 A SQL subquery is a nested query; that is, it is a query that is nested within another query. You can use subqueries with the same clauses that you can use them in. So far, in this chapter, we have focused on only one way of retrieving data, which is the SELECT statement. Next, we look at how to retrieve data from a relational database using a subquery within a SELECT statement and also how to perform INSERT, UPDATE, and DELETE commands using subqueries. Here is a subquery example: 

 

```sql

SELECT first_name, last_name 

FROM employees 

WHERE department_id IN (SELECT id FROM departments WHERE department_name = 'Sales');

```

 

Performance Tuning in SQL

The Importance of Indexes

 For optimal efficiency, a database must rely on properly written, performance-tuned SQL. What does "tuned" mean in this context? Mostly, it means getting the most out of your indexes. In SQL, an index is a database object that serves as a reference point. If you use SQL to issue a database command.

 

Conclusion

SQL is a crucial tool for people working with data. Its ability to control and direct large quantities of data makes it fundamental to all sorts of large-scale data operations, such as the ones that go on in contemporary internet businesses. Even a nascent data scientist with big dreams must grapple with SQL if she hopes to work with datasets as large as those of her forebears. This language isn't quite as accessible as some others, but there are plenty of resources that can help you learn it. I've rounded up a few of the best and most accessible. They will help you not just to get the hang of the basic commands you need to write and run but also to understand some important underlying principles for why things work as they do.