queries & SQL

queries & SQL

1. DATA BASES

   • data bases can be queried through a variety of different ways
     • query language
       • Query language is a written language used only to write specific queries. This is a powerful tool as the user can define precisely what is required in a database.
     • query by example
       • QBE allows the user to create queries based on a template, usually a set of filters presented in a graphical form.

2. Boolean operators

   • In a database we often need to filter the data to group certain results. Boolean operators are used to filter databases using AND, OR or NOT.
     • AND
       • AND is used to search records that contain one piece of information AND another.
     • OR
       • OR is used to search for records that contain EITHER one piece of information OR another.
     • NOT
       • NOT is used to exclude results.E.g. The query shoes NOT brown will return results that contain the word shoes but NOT the word brown.

3. Arithmetic operators

   • A query can also be performed using arithmetic operators. These help to make specific searches related to numerical data.