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SQL - Structured Query Language

An English-like programming language, which is used for communicating with relational database management systems (RDBMS).

SQL is used in most common databases, including:

  • Microsoft SQL Server and Access
  • MySQL
  • PostGreSQL
  • Oracle
  • FireBird (InterBase)
  • IBM DB2
  • SAP DB

Example SQL query - get the ID, name and price, of all products under $50:

select product_id, product_name, product_price
from products
where product_price < 50

Example SQL query results:

product_id product_name         product_price
---------------------------------------------------
7          small widget                 84.95
12         large widget                112.95
19         ultra-compact widget        899.95

The most basic SQL commands are:

  • SELECT - for selecting data
  • INSERT - for inserting data
  • DELETE - for deleting data
  • UPDATE - for updating data

There are also commands for creating and manipulating database tables. While there are standards for the SQL language, each database has it's own specific extensions or dialect for performing more complicated tasks.

Almost all current programming languages can communicate with databases using SQL, as long as a driver or connector is available, to bridge the gap between the language and the physical database.

In Java, the JDBC technology is used to execute SQL statements. The query results are returned in objects which can be iterated through to process or display the data.

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