SQL

Retrieving your data.

Your best database is of little use if you can’t access and manipulate the data.That’s where SQL comes in, giving your valuable data an actual usable value.

SQL found its inception at IBM in the 1970’s. It was originally called SEQUEL, which stands for “Structured English Query Language”, but due to trademarking issues, the name was shortened to SQL. SQL is a language that is designed to manipulate and retrieve data, and is most often used for queries which are used to retrieve data from a database.

How SQL Works

SQL preforms database queries through a clause including a:

  • From Clause
  • Where Clause
  • Group by Clause
  • Having Clause
  • Order by Clause

Subqueries allow one query to automatically generate or affect a subsequent query. A subquery can use values from an outer query, which is also referred to as a correlated subquery.

Language Elements

  • Clauses
  • Expressions
  • Predicates
  • Queries
  • Statements

DML: Database Manipulation Language

A Data Manipulation Language (DML) is generally a subset of SQL that allows a developer to add, update and delete data. Therefore, the DML is often used as a tool by developers to keep databases in sync with entries that are inputted into an application by an external application user.

adamSQL