Structured Query Language (SQL) is a language to query relational databases.
You can read this post that is an introduction to relational databases.
SQL Variants
There are variants to SQL. For example, PL/SQL (Procedural Language for SQL) is an extension developed by Oracle.
Common SQL Commands
Common SQL commands:
- Data Definition Language (DDL)
- CREATE
- ALTER
- DROP
- TRUNCATE
- Data Manipulation Language (DML)
- INSERT
- DELETE
- UPDATE
- Data Query Language (DQL)
- SELECT
- Data Control Language (DCL)
- GRANT
- REVOKE
- Transaction Control Language (TCL)
- COMMIT
- ROLLBACK
- SAVEPOINT
DROP deletes the table structure with its content.
TRUNCATE deletes only the content of a table, leaving the structure.
DELETE deletes some rows under certain conditions.
WITH allows you to define Common Table Expressions (CTEs), which are temporary subqueries that can be referenced within the main query.
SQL Security
SQL injection is one of the most recurring issues in websites.
SQL injection queries examples
Tools to detect SQL injection vulnerabilities