SQL: What Is It and How Does It Work?

SQL is a standard language for accessing and manipulating data stored in relational databases. SQL stands for Structured Query Language, and it is widely used by data analysts, data scientists, web developers, and other professionals who work with data. In this article, we will explain what SQL is, how it works, and what it can do.

What is SQL?

SQL is a domain-specific language that allows users to communicate with databases using queries. A query is a statement that specifies what data you want to retrieve, insert, update, delete, or manipulate from a database. SQL queries are composed of keywords, clauses, expressions, operators, and functions that follow a specific syntax.

SQL was developed in the 1970s by IBM researchers as a way to interact with relational database management systems (RDBMS). A RDBMS is a software that organizes data into tables, which consist of rows and columns. Each row represents a record, and each column represents a field or an attribute of the record. For example, a table of customers may have columns such as CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country.

SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987¹. However, there are different versions and dialects of SQL that are used by different RDBMS vendors, such as MySQL, Oracle, SQL Server, PostgreSQL, SQLite, etc. These versions may have their own extensions and features that are not part of the standard SQL. However, they all support at least the major commands and syntaxes of the standard SQL.

How Does SQL Work?

To use SQL, you need to have access to a RDBMS that stores the data you want to work with. You also need to have a tool or an application that allows you to write and execute SQL queries. This can be a graphical user interface (GUI) tool, such as MySQL Workbench or Microsoft SQL Server Management Studio; or a command-line interface (CLI) tool, such as mysql or sqlcmd. Alternatively, you can use a programming language, such as Python or PHP, to connect to a database and run SQL queries from your code.

When you write and run an SQL query, it is processed by the RDBMS in several steps:

• Parsing: The RDBMS checks the syntax and semantics of the query to make sure it is valid and meaningful.
• Binding: The RDBMS checks the permissions and access rights of the user who runs the query to make sure they are authorized to access the data.
• Optimization: The RDBMS generates an execution plan for the query, which is the most efficient way to retrieve or manipulate the data.
• Execution: The RDBMS executes the query according to the execution plan and returns the result set or an error message.

What Can SQL Do?

SQL can perform various operations on data stored in relational databases. Some of the most common operations are:

• Retrieving data: You can use the SELECT statement to query data from one or more tables based on certain criteria. You can also use clauses such as WHERE, GROUP BY, HAVING, ORDER BY, and LIMIT to filter, aggregate, sort, and limit the result set. You can also use functions such as COUNT, SUM, AVG, MIN, MAX, etc. to perform calculations on the data. You can also use JOINs to combine data from multiple tables based on common fields.
• Inserting data: You can use the INSERT statement to add new records to a table. You can specify the values for each column or use a subquery to insert data from another table.
• Updating data: You can use the UPDATE statement to modify existing records in a table. You can use the SET clause to specify the new values for each column and use the WHERE clause to specify which records to update.
• Deleting data: You can use the DELETE statement to remove existing records from a table. You can use the WHERE clause to specify which records to delete.
• Creating data: You can use the CREATE statement to create new databases, tables, views, indexes, triggers, stored procedures, functions, etc. You can specify the name, structure, constraints, and options for each object.
• Altering data: You can use the ALTER statement to modify existing databases,