What Is SQL? (With Uses, Commands, Statements and FAQs)

By Indeed Editorial Team

Published 26 April 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Programming languages are languages that allow people to use special codes to tell a machine, such as a computer, to perform a certain task. One common example is SQL, which professionals in many industries use to store and retrieve data from computers. Learning about SQL can help you decide if you want a career that involves understanding and using this programming language in the workplace. In this article, we define SQL, explore important elements of the language and provide answers to frequently asked questions about SQL.

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What is SQL?

Structured Query Language (SQL) is a programming language that can communicate with and change databases. Pronounced as 'S-Q-L' or 'sequel,' SQL is a user-friendly domain-specific programming tool that is compatible with many platforms. This language can handle large amounts or small amounts of data, and many technology-focused fields often use it to extract and organise information in databases. Examples of professionals who may use SQL include:

  • software developer

  • programmer

  • data analyst

  • database administrator

  • web designer


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Uses for SQL

Data professionals use SQL to extract data and transpose it so that they can analyse the data. SQL is also useful for organising data. Most often, SQL is used to work with relational databases, which have a special structure to recognise relationships between data points when it stores information. Databases are collections of tables that store data in rows, called records or tuples, and columns, called attributes. Each column stores specific, structured data, such as names, numbers or dollar amounts.

SQL allows you to manipulate objects in the database, such as tables that store data according to its relation to other data. You can also use SQL to add or delete tables. To manage the stored data, you may edit tables and create permissions and procedures for those assessing the data. Additionally, SQL makes it possible to retrieve, edit and create records in the database. This is an important use for data analysts and data scientists who may collect data for marketing, product development, financial or business operations.

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SQL is a programming language used to operate relational databases within relational database management systems (RDBMS). An RDBMS is a programme that stores and maintains a database to ensure its security, accuracy and organisation. It can also help preserve the integrity of an organisation's data. SQL is primarily used in business applications to help companies store, retrieve and secure data.

NoSQL, which stands for 'not only SQL', is not a language but a type of database management system. NoSQL database management systems maintain databases that are non-relational, which means they do not store data in tables. Professionals in tech often use NoSQL databases for large, web-based applications with large amounts of data. NoSQL databases do not use SQL, but they're compatible with many other common programming languages.

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SQL commands

An SQL command is a word or phrase that tells a relational database what to do. For example, it might tell the database to create an element, such as a table. Professionals often combine SQL commands to perform specific SQL tasks and functions and create queries, which are requests for data. For example, they may combine CREATE, which creates a new database or table, with TABLE to specify which element they want to create. When they enter CREATE TABLE, the database adds a new table. Here are some other common SQL commands you can use to operate an RDBMS:

  • DROP: The DROP command deletes a table or database.

  • ALTER: The ALTER command changes the structure of a database or column.

  • TRUNCATE: The TRUNCATE command removes existing records from the table.

  • INSERT: The INSERT command adds rows of data into an existing table.

  • UPDATE: The UPDATE command updates a table with new data based on specific conditions.

  • DELETE: The DELETE command removes data from a table based on specific conditions.

  • GRANT: The GRANT command gives a user or users access to a database.

  • REVOKE: The REVOKE command revokes user database permissions.

  • COMMIT: The COMMIT command saves transactions to the database.

  • ROLLBACK: The ROLLBACK command reverses transactions the user has not saved to the database.

  • SAVEPOINT: The SAVEPOINT command takes the user back to a certain point without deleting the transaction.

  • SELECT: The SELECT command selects a certain attribute based on specific conditions.

  • DATABASE: DATABASE is a command a user adds to another command, such as DROP or CREATE, to add or change a database.

  • AVG(): The AVG() command returns the average of the values in a column.

  • SUM(): The SUM() command returns the sum of the values in a column.

  • ROUND(): The ROUND() command rounds the values in the column to a specific number of decimal places.

  • MAX(): The MAX() command returns the largest value in a column.

  • MIN(): The MIN() command returns the smallest value in a column.

  • COUNT(): The COUNT() command counts the number of rows where the column does not have a NULL value.

Types of statements

A statement is a combination of SQL commands you can use to perform tasks in an RDBMS. There are several types of statements you can use for different purposes. Here are some of the common type of SQL statements:

  • Data Definition Language (DDL) statement: A DDL statement is one that allows you to create or change database elements. DDL commands include CREATE, DROP, ALTER and TRUNCATE.

  • Data Manipulation Language (DML) statement: A DML statement is one that allows you to manipulate data in a database. DML commands include INSERT, UPDATE and DELETE.

  • Data Control Language (DCL) statement: A DCL statement is one that allows you to control access to the information a database stores. DCL commands include GRANT and REVOKE.

  • Transaction Control Language (TCL) statement: A TCL statement is one that allows you to manage transactions in a database. TCL commands include COMMIT, ROLLBACK and SAVEPOINT.

  • Data Query Language (DQL) statement: A DQL statement is one that retrieves data from a database. SELECT is the only DQL command.

SQL processing steps

SQL processing refers to the steps a database takes to process SQL statements. The specific process depends on the statement, but there's a standard procedure relational databases use for most statements. Here are the four general SQL processing steps:

  1. Parsing: During parsing, the database separates the pieces of the SQL statement to create a data structure it can process in the next steps.

  2. Optimisation: Next, the database selects an efficient method for evaluating the parsed data in a process called optimisation.

  3. Row source generation: After optimisation, a row source generation programme receives the plan and decides how to execute it so the database can use it.

  4. Execution: During the execution plans, the database uses the input data to make changes and return queries accordingly.

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FAQs about learning and using SQL

If you're considering a career that would involve using SQL, you may have questions. Here are some frequently asked questions and answers about learning and using SQL:

Is SQL easy for beginners to learn?

Any programming language can be challenging if you don't have experience using them, but some professionals who code recommend SQL as the first programming language to learn. This is because SQL commands are typically basic English words instead of complex code formats. It also relies on a logical process that users often find easy to understand once they learn its systematic nature.

What is the SQL order of execution?

The SQL order of execution is the way to format a query to ensure it returns the correct data. The order of execution starts with identifying a piece of data, then continues with commands that filter the data to meet specifications. After inputting the required command for each line, you can add other commands to make them more specific. Here is the order of execution for SQL queries:

  1. FROM defines where you want the database to find the data.

  2. WHERE allows you to add filters to specify the data.

  3. GROUP BY allows you to aggregate your data.

  4. HAVING allows you to filter the data you aggregated.

  5. SELECT displays the data.

  6. ORDER BY allows you to sort the data.

  7. LIMIT restricts the number of results you receive.

What are SQL standards?

SQL standards are the rules of the language that establish its correct usage. There are different versions of SQL, but they all use the major SQL commands, such as CREATE, INSERT, SELECT and UPDATE. This allows each SQL version to adhere to the standards the International Organization for Standardization (ISO) maintains for SQL languages.

How can I improve my SQL skills?

Learning a new programming language takes time, but there are ways you may improve your understanding of SQL faster. Here are some tips to help you master SQL:

  • Observe colleagues who use SQL at work.

  • Practise SQL by writing sample processes.

  • Take on SQL freelance work to get practical experience.

  • Start with the basics, and then focus on more complex processes.

  • Offer to help a friend learn SQL to refresh your memory and skills.

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