SQL queries 101

Learning SQL queries

SQL queries are instructions that you send to a database management system (DBMS), such as Microsoft SQL Server, Oracle, or MySQL, to retrieve, manipulate, or modify data stored in the database.

SQL stands for Structured Query Language, and the queries written in SQL are used to perform operations such as:

• SELECT: Retrieve data from the database tables.
• INSERT: Add new data to the database tables.
• UPDATE: Modify existing data in the database tables.
• DELETE: Remove data from the database tables.

A query consists of several elements, including keywords, clauses, and conditions, which are combined to form a complete instruction.

For example, the following is a simple SELECT query:

SELECT first_name, last_name, email 
FROM customers
This query retrieves the first_name, last_name, and email columns from the customers table in the database. The keywords used in the query are SELECT and FROM, and the clauses used are first_name, last_name, email and customers.
In simple terms, a SQL query is a request you make to a database to retrieve or manipulate data stored in it.