What is Structured Query Language (SQL)? #
Structured Query Language (SQL) is a programming language specifically designed for managing and manipulating relational databases. SQL provides a standardised way to interact with databases, allowing users to create, modify, and query data stored in a structured format.
SQL is used by various database management systems (DBMS), such as Microsoft SQL Server, MySQL, PostgreSQL, Oracle Database, and SQLite. It is widely used in software development, data analysis, and database administration for tasks like managing data, generating reports, and extracting insights from large datasets.
What is SQL used for? #
Relational databases consist of tables that store data organised into rows and columns. SQL enables users to perform various operations on this data. The database management system (DBMS) interprets the SQL statements and determines the most efficient way to execute them. This can include:
- Creating and modifying database schemas: SQL allows users to define the structure of a database by creating tables, specifying columns, data types, and relationships between tables.
- Inserting, updating, and deleting data: SQL provides commands for adding, modifying, and removing data within a database. Users can insert new records into tables, update existing records, or delete records that are no longer needed.
- Querying and retrieving data: SQL enables users to retrieve specific data from one or more tables using SELECT statements. It allows for filtering, sorting, grouping, and aggregating data based on various criteria.
- Managing database access and security: SQL provides mechanisms to control user access to databases, granting or revoking permissions to perform specific actions. It allows administrators to define user roles, set privileges, and ensure data security.
- Creating views, indexes, and stored procedures: SQL supports the creation of views, which are virtual tables derived from one or more tables. It also allows the creation of indexes to optimise data retrieval and stored procedures to encapsulate frequently used operations.
What are SQL commands? #
SQL commands are used to carry out the various operations listed above. A SQL command refers to a statement or instruction written in the SQL programming language.
SQL commands are executed against a database management system (DBMS) that understands and interprets the SQL language.
Each command has a specific syntax and purpose, and understanding SQL commands is crucial for working with databases efficiently.
Some common SQL commands include:
- SELECT: Retrieves data from one or more tables in the database.
- INSERT: Adds new rows of data into a table.
- UPDATE: Modifies existing data in a table.
- DELETE: Removes rows from a table.
- CREATE: Creates database objects, such as tables, views, indexes, or stored procedures.
- ALTER: Modifies the structure of an existing database object.
- DROP: Deletes a database object.
- JOIN: Combines rows from two or more tables based on related columns.
- WHERE: Filters data in a query based on specified conditions.
- GROUP BY: Groups rows based on specified columns.
- ORDER BY: Sorts the result set based on one or more columns.
- HAVING: Filters grouped data in a query based on specified conditions.
What are the benefits of SQL? #
SQL’s benefits include its ease of use, standardisation, powerful data manipulation capabilities, scalability, data integrity, security features, integration with other programming languages, and support for complex operations. These advantages have made SQL a dominant language for managing relational databases and a valuable skill for data professionals and developers.
SQL is an industry-standard language for interacting with relational databases and is supported by most major database management systems, ensuring portability and compatibility across different platforms.
SQL’s straightforward language is relatively easy to learn and understand, and allows users to express what they want to retrieve or modify from a database without specifying how to do it. This simplicity makes SQL accessible to both experienced programmers and beginners, and can be applied to various database systems.
SQL can be seamlessly integrated with other programming languages, allowing developers to incorporate database operations into their applications. This integration enables the development of data-driven applications and simplifies the retrieval and storage of data.
SQL databases are designed to handle large volumes of data and support concurrent access from multiple users. It provides a rich set of commands for querying, filtering, sorting, and aggregating data, enabling users to perform complex operations on these large datasets efficiently. It also allows for indexing, which enhances data retrieval speed, and provides mechanisms for optimising query performance.
SQL includes mechanisms to enforce data integrity rules, such as constraints and referential integrity. These features help maintain data accuracy and consistency. It also provides security features for controlling access to databases, protecting sensitive data, and managing user privileges.