Manipulating Data

Manipulating Data

A set of relational operators have been defined to manipulate relational databases. Basic data manipulation operators include select, project & join.

Select - eliminate rows according to certain criteria.

A select operation reduces the length of a table by filtering out unwanted rows. By specifying conditions in the where clause, the user can filter unwanted rows out of the result set, the select operation reduces the results vertically.

Project - eliminate columns in a table.

Just as the select operation reduces the number of rows, the project operation reduces the number of columns. The column names specified in the SQL select determine those columns that are displayed,  the project operation reduces the size of the result set horizontally.

Join - combine two or more tables.

A join operation such as used to relate two or more independent tables that share a common column. In a join, two or more independent tables are merged according to a common column value.

Data organize in tables can be easy to manipulate and one of the primary advantages of a relational database is that it allows tables to be linked using common data attributes, which help to produce useful information and reports and also allows users to relate data in new ways without having to redefine complex relationships.

Data Manipulation Language (DML) commands are used to manipulate the data in database. The DML, with the DBMS allows database users to access, modify and make queries about the data that contained in the database.

SQL (Structured Query Language) is the data manipulation language for relational databases. Once a database has been set up and loaded with data, it can produce desired reports, documents and other outputs. By the output control feature a database program allows to select the records and fields to appear in reports.