Statements and Queries in SQL

1. Introduction

Structured Query Language (SQL) is a standard programming language widely used for managing and manipulating relational databases. It includes various elements, such as queries, statements, clauses, expressions, and predicates, each serving a specific function in database management.

In this tutorial, we’ll start by introducing all the elements in SQL. Then, we’ll concentrate on two of these elements: SQL queries and statements. Lastly, we’ll explore their distinctions and give useful examples for each.

2. SQL Syntax and Language Elements

SQL is a declarative language, meaning we tell it what we want, and it figures out how to do it. It includes a variety of elements to construct commands. There are seven key elements in SQL:

• Keywords are reserved words that have a special interpretation in SQL. Common examples include SELECT, INSERT, UPDATE, DELETE, WHERE, and FROM.
• Identifiers refer to the names of database objects, such as tables and columns.
• Expressions are combinations of one or more values, operators, and SQL functions that evaluate to a single value.
• Queries use certain criteria to retrieve data, which is a crucial component of SQL.
• A statement is any command or instruction given to a relational database management system using SQL. This command can serve a variety of purposes, such as retrieving data, updating data, or modifying the database structure.
• Clauses are a component of SQL queries and statements. For instance, WHERE, ORDER BY, and GROUP BY are some of the popular clauses used in SQL.
• Predicates define the conditions that SQL evaluates as true, false, or unknown. These conditions can affect the outcome of SQL statements and queries or change the way programmers write and run the code.

The figure below illustrates the key elements of SQL:

3. Difference Between Query and Statement

The terms SQL statement and SQL query are sometimes used interchangeably, but there are key differences between them. Let’s explore what they are.

3.1. SQL Statements

An SQL statement is a command issued to the database for performing various tasks such as retrieving data, updating records, or manipulating the database structure.

SQL statements include queries (commands for retrieving data) and encompass a wider set of operations, such as:

• INSERT: Adds new data (rows) to a table
• UPDATE: Modifies existing data within a table
• DELETE: Removes data from a table
• CREATE: Creates a new database object, such as a table or view
• ALTER: Modifies an existing database object
• DROP: Deletes a database object

Each of these statements helps users interact and manipulate the data and the structure of the database in different ways, making SQL a flexible and powerful language for managing relational databases.

Let’s look at an example INSERT statement:

INSERT INTO Customers (CustomerName, ContactName, Country)
VALUES ('Cardinal', 'Tom B. Erichsen', 'Norway');

In this example, the INSERT statement adds a new row of data to the Customers table.

3.2. SQL Queries

SQL queries are a subset of SQL statements that return data based on specific criteria. They’re used specifically to retrieve data from the database, and they do this using the SELECT statement. Let’s see a simple SQL query using the SELECT statement:

SELECT CustomerName, Country 
FROM Customers 
WHERE Country='USA';

This query returns the names and countries of all customers from the Customers table located in the USA.

In essence, all queries are statements, but not all statements are queries. A query is a statement that retrieves data, while statements can do this and much more, including modifying data and altering the database structure.

4. Conclusion

In this article, we talked about the elements of SQL, including keywords, identifiers, expressions, queries, statements, clauses, and predicates. It’s common to use the terms statements and queries interchangeably. However, they do have distinct meanings and serve different purposes. Understanding the distinction between SQL statements and queries is essential for anyone working with SQL.

A query is a statement that specifically retrieves data and helps clarify their unique roles within the SQL language using the SELECT operation. On the other hand, statements include a broader set of operations, such as INSERT, UPDATE, DELETE, CREATE, ALTER, and DROP.