SQL Introduction

SQL (Structured Query Language) is a programming language used for managing and manipulating relational databases. It can be used to insert, update, and retrieve data from a database, as well as to create and modify the structure of a database. SQL Introduction

Some of the common operations that can be performed using SQL include selecting data from tables, inserting new data into tables, updating existing data, and deleting data. It is a standard language for Relational Database Management Systems (RDBMS) such as MySQL, PostgreSQL, Microsoft SQL Server, Oracle, and many others.

History of SQL

SQL (Structured Query Language) was first developed by IBM in the 1970s. The first version, SEQUEL (Structured English Query Language), was used by IBM to manage data in its System R relational database management system. The name was later changed to SQL, and the language was standardized by the American National Standards Institute (ANSI) in 1986, and by the International Organization for Standardization (ISO) in 1987.

Since then, several versions of SQL have been released, including:

  • SQL-86 (ANSI standard)
  • SQL-89 (ANSI and ISO standard)
  • SQL-92 (ANSI and ISO standard)
  • SQL:1999
  • SQL:2003
  • SQL:2006
  • SQL:2008
  • SQL:2011
  • SQL:2016
  • SQL:2019

Each version of SQL has added new features and capabilities to the language, such as support for nested queries, data types, and transactional control. The latest version is SQL:2019 which was released in 2019.

The purpose of SQL (Structured Query Language) is to manage and manipulate data in relational databases. SQL is used to insert, update, and retrieve data from a database, as well as to create and modify the structure of a database. Some of the main features and capabilities of SQL include:

  1. Data Definition Language (DDL): SQL includes commands for creating and modifying the structure of a database, such as creating tables, adding columns, and setting primary keys.
  2. Data Manipulation Language (DML): SQL includes commands for inserting, updating, and deleting data in a database, such as SELECT, INSERT, UPDATE, and DELETE.
  3. Data Control Language (DCL): SQL includes commands for controlling access to the data in a database, such as GRANT and REVOKE.
  4. Data Query Language (DQL): SQL includes commands for retrieving data from a database, such as SELECT, which is used to retrieve specific data from one or more tables.
  5. Data Aggregation: SQL includes commands for computing the aggregate values of data in a database, such as COUNT, SUM, AVG, MIN, and MAX.
  6. Data Joining: SQL includes commands for joining data from multiple tables together, such as JOIN, which is used to retrieve data from multiple tables in a single query.
  7. Data Constraints: SQL includes commands for setting constraints on the data in a database, such as NOT NULL and UNIQUE, which are used to ensure data integrity and consistency.
  8. Data Transactions: SQL includes commands for handling transactions, such as COMMIT and ROLLBACK, which are used to make sure data is consistent across multiple statements.
  9. Data indexing: SQL includes commands for indexing data, which is used to improve the performance of the queries.

SQL is a standard language and it’s widely used in most of the RDBMS(Relational Database Management Systems) like MySQL, Oracle, MS SQL Server, PostgreSQL and many more.

Here is a list of some common SQL commands and a brief description of their uses:

Data Definition Language (DDL) Commands:

  • CREATE: Used to create a new table, index, or database.
  • ALTER: Used to modify the structure of an existing table, index, or database.
  • DROP: Used to delete an existing table, index, or database.
  • TRUNCATE: Used to remove all data from a table, but not the table structure.

Data Manipulation Language (DML) Commands:

  • SELECT: Used to retrieve data from one or more tables.
  • INSERT: Used to insert data into a table.
  • UPDATE: Used to modify data in a table.
  • DELETE: Used to delete data from a table.

Data Control Language (DCL) Commands:

  • GRANT: Used to give users access to specific database objects.
  • REVOKE: Used to remove access to specific database objects.

Transaction Control Commands:

  • COMMIT: Used to save changes made to the database.
  • ROLLBACK: Used to undo changes made to the database.
  • SAVEPOINT: Used to set a point in a transaction to which you can later roll back.

Some additional commands are also available to manage indexes, views and many more, however, the above mentioned commands are the most commonly used in SQL. It’s also important to note that different DBMS (like MySQL, PostgreSQL, SQL Server, Oracle) may have different variations of the commands and their usage.