SQL Glossary: Your Ultimate Guide to SQL Terms

SQL (Structured Query Language) is a specialized programming language designed for managing and manipulating relational databases. It is the standard language for relational database management systems and is used for tasks such as querying data, updating databases, and managing database structures. SQL plays a critical role in data analysis, web development, and beyond, as it allows users to retrieve and organize data efficiently from large databases.

You can use the terms in this SQL glossary to familiarize yourself with essential terminology. Whether you’re preparing for a certification in database management, gearing up to interview for a data-intensive role, or simply aiming to enhance your programming skills, studying these SQL terms will empower you to navigate databases more effectively and confidently.

SQL terms

You’ll find common SQL  terms in the glossary below.

Aggregate Functions

Aggregate functions calculate a set of values and return a single value. Common examples include SUM(), AVG(), MIN(), MAX(), and COUNT().

Alias

An alias is a temporary name assigned to a table or column within an SQL query. Aliases help simplify complex queries and improve readability.

Backup and Recovery

These terms refer to the strategies and processes involved in protecting your database against data loss and reconstructing the data should a loss occur. Understanding different backup strategies and how to recover from various types of failures is crucial.

Constraints

Constraints are rules enforced on data columns on a table. They are used to prevent invalid data from being entered into the database. This ensures the accuracy and reliability of the data. Typical constraints include PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, and CHECK.

Data Manipulation Language (DML)

DML refers to the subset of SQL used to add, update, and delete data within a database. Common DML commands include INSERT, UPDATE, and DELETE.

Data Definition Language (DDL)

DDL comprises SQL commands used to define or modify database structures. Typical DDL statements include CREATE, ALTER, and DROP.

Data Governance

This is the overall management of the availability, usability, integrity, and security of the data employed in an enterprise. A good governance plan ensures that data is consistent and trustworthy and doesn't get misused.

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Data Warehousing

A data warehouse is a system used for reporting and data analysis. It is a central repository of integrated data from one or more disparate sources, used for query and analysis rather than transaction processing.

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Foreign Key

A foreign key is a field (or collection of fields) in one table that refers to the primary key in another table. It establishes and enforces a relationship between the two tables, helping maintain referential integrity.

Index

An index in SQL speeds up data retrieval by creating a pointer to data in those columns. Indexes can be created on one or more columns of a database table.

Join

A join is an SQL operation that combines rows from two or more tables based on a related column between them. Several types of joins exist, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN.

Normalization

Normalization is organizing data in a database to reduce redundancy and improve data integrity. It involves dividing large tables into smaller, interrelated tables and defining relationships.

Performance Tuning

Performance tuning involves optimizing database performance through various means, such as indexing, query optimization, and system hardware upgrades.

Primary Key

The schema is a container of objects belonging to a database user. It can limit or contain the data that the user can access and is often used as a security measure.

Query

A query requests data or information from a database table or combination of tables. This SQL command retrieves data that meets the criteria you specify.

Schema

A schema is the organization or layout of a database that defines the tables, fields, relationships, views, indexes, and other elements.

SQL Injection

This term describes a type of security vulnerability in which an attacker can execute malicious SQL statements that control a web application's database server. Understanding SQL injection is crucial for developing secure SQL applications.

Stored Procedure

A stored procedure is a prepared SQL code that you can save so the code can be reused repeatedly. Stored procedures can be invoked explicitly by the user.

Subquery

A subquery is a query nested inside another query. It's used to perform operations that require multiple steps in SQL, such as when the output of one query serves as the input of another.

Transaction (Transact-SQL)

A transaction in SQL is a single unit of work completed in its entirety or not at all. Critical properties of transactions include Atomicity, Consistency, Isolation, and Durability (ACID).

Trigger

A trigger is an SQL procedure that initiates an action in response to an event (such as INSERT, UPDATE, or DELETE) occurring in a database. It's used to maintain the integrity of the data across several tables.

View

A view is a virtual table based on the result set of an SQL statement. It contains rows and columns, just like a real table. The fields in a view are from one or more real tables in the database.

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