Joins in SQL

SQL is a well-known database computer language that is beneficial in retrieving and managing the data in a relational database management system. Most of you may have heard of Structured Query Language, now popularly known as SQL. To understand Joins in SQL, you must first understand what SQL is. There are billions of data produced every hour across the country, and to manage these data, you must have appropriate tools and techniques. SQL is known as a Structured Query Language that helps you out with all the database queries. Many companies use SQL to handle their databases, and Programmers find it easy to learn and operate. SQL allows you to store, manipulate, and retrieve the data stored in the relational database.

It is known that the Relational Database System is the one most used, and to manage these relational database systems, many have claimed that SQL is the standard language. You may have come across many RDBMS like Oracle, MySQL, and more. But must know the fact that all these RDBMS makes use of SQL as their standard database language. Also, they are making use of various dialects like Oracle uses PL/SQL, MS SQL Server uses T-SQL, etc. When you execute an SQL command for any RDBMS, the system tries to figure out the best way to process your request, and the SQL engine finds the best way possible to interpret the task. This process involves multiple components like Query Dispatcher, Optimization Engines, Classic Query Engine, SQL Query Engine, etc. 

You have to know the standard commands in SQL used for interaction with relational databases: CREATE, SELECT, INSERT, UPDATE, DELETE, and DROP. These commands can be further classified into several groups based on their nature.

DDL (Data Definition Language)

1) CREATE : This command allows you to create a new table, a view of the table, and other objects in the database.

2) ALTER : This command is utilized for modifying an existing database object like a table.

3) DROP : This command is for deleting a complete table, a view of a table, or other objects in the database.

DML (Data Manipulation Language)

1) SELECT : This command allows you to retrieve specific records from one or multiple tables.

2) INSERT : This command helps you in creating a record and inserting values in it.

3) DELETE : This command allows you to delete the records specified.

DCL (Data Control Language)

1) GRANT : Grant command provides certain privileges to users.

2) REVOKE : Revoke command is used for taking back the privileges granted to the user.

You may face various situations where you need the combined details from the multiple tables in the database. To get solutions for the above scenarios, you must first understand the Joins in SQL concept. The SQL Joins clause allows you to combine data from multiple tables present in the database. The Join operation in SQL is a means through which you can combine fields from multiple tables by using multiple common values present. Joins in SQL are usually performed in the WHERE clause. You can also utilize several operators to join tables like =, <, >, <>, <=, > =, !=, LIKE, BETWEEN, and NOT. The most commonly utilized operator here is equal to symbol. There are various types of Joins in SQL that help you achieve your goal of combining the data in the tables.

The different types of Joins in SQL are:

• INNER JOIN : Inner Join returns the rows whose matches are found in both tables.

• LEFT JOIN : Left Join returns entire rows present in the left table and returns only matched rows from the right table. Even if no matched rows are found in the right table, this Join returns all the left table rows.

• RIGHT JOIN : Right Join returns entire rows present in the right table and returns only the matched rows of the left table. Even if no matched rows are found in the left table, this Join returns all the right table rows.

• FULL JOIN : Full JoinJoin returns the rows when a matched row is found in one of the tables.

• SELF JOIN : Self Join allows you to create a join with that specific table itself. It assumes the targeted table as two and temporarily renames at least one of the tables in the SQL statement.

• CARTESIAN JOIN : In this JoinJoin, you can have multiple joined tables, and this JoinJoin gives you the cartesian product of the sets of values from the joined tables.

These Joins in SQL are very helpful when you manage vast databases where you have to face scenarios in which you have to find the common values. These Joins in SQL come in handy while solving such problems. Joins in SQL is a must-learn concept as many queries are related to joins, and many results are attained through these Joins in SQL. Many concepts and queries in SQL are all related to Joins. Joins have made it easier for many to retrieve common values from various tables in the database, without which it would be challenging to retrieve common rows from a bundle of tables. Hence, learning Joins in SQL is very essential.

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