What is SQL?

SQL (Structured Query Language) is a standard programming language designed for managing relational databases. It’s used for querying, inserting, updating, and deleting data from databases, as well as for defining database schemas, creating and modifying tables, and managing database users and permissions.

SQL is used to insert, search, update, and delete database records (and a fancy term used for such operation is known as CRUD).

Here are some key aspects of SQL:

1. Data Querying: SQL allows users to retrieve data from a database using queries. Queries are structured statements that specify the criteria for selecting data from one or more tables. The SELECT statement is the primary SQL command used for querying data.
2. Data Manipulation: SQL provides commands for manipulating data within a database. These commands include INSERT (for adding new rows of data), UPDATE (for modifying existing data), and DELETE (for removing data).
3. Data Definition: SQL includes commands for defining and modifying the structure of a database. These commands allow users to create and drop tables, define constraints (such as primary keys and foreign keys), create indexes for efficient data retrieval, and alter table structures.
4. Data Control: SQL provides commands for managing database users and their permissions. These commands allow administrators to grant or revoke access privileges to specific database objects (such as tables, views, and stored procedures) for different users or user groups.
5. Transaction Control: SQL supports transaction management, which ensures the integrity and consistency of database operations. Transactions are sequences of SQL commands that are executed as a single unit, either entirely or not at all. SQL provides commands like COMMIT (to save changes made by a transaction) and ROLLBACK (to discard changes and restore the database to its previous state).
6. Data Integrity: SQL supports various constraints and integrity rules to maintain data consistency and accuracy. These include primary key constraints (to ensure unique identification of rows), foreign key constraints (to enforce referential integrity between related tables), and check constraints (to enforce specific data validation rules).

SQL is a standardized language, but different database management systems (DBMS) may implement variations or extensions of the standard. Some popular relational database systems that use SQL include MySQL, PostgreSQL, Oracle Database, SQL Server, SQLite, and MariaDB. Despite some differences in syntax and features, the core SQL language remains consistent across these systems.

How to use SQL

The following SQL statement selects all the records in the “Employees” table:

• SELECT * FROM EMPLOYEES

SQL keywords are NOT case sensitive: select is the same as SELECT