Relational Algebra Essay

633 Words2 Pages

2.2.1 RELATIONAL ALGEBRA

Relational algebra is a set of operators used to perform operations on tables. Operators in Relational Algebra takes one or more tables as parameters and produce one table as the result (Sharma, R. 2013).

The following are operators in “Relational Algebra”:
• Union - takes two tables, and returns all rows that are belonging to: both tables or, either first table or either second table.
• Intersect - takes two tables, and returns all rows that are belonging only to the first table and to the second table.
• Difference/Minus - takes two tables, and returns all rows that exist only in the first table, not in the second one.
• Project - takes a single table, and returns the “vertical subset” of the table.
• Select …show more content…

So, rows of two table are combined, based on given column values (Sharma, R. 2013).

2.2.2 STRUCTURED QUERY LANGUAGE (SQL)

SQL stands for Structured Query Language, is the standard language used in all relational database management systems for data manipulation and retrieval (Tomar, N. 2013). Structured Query Language is a “non-procedural language”, where you need to concentrate on: “What you want” not on “How you get it”, in other words you do not need to be concerned with procedural details.

Depending upon what they do, SQL Commands are divided into four categories:
DDL (Data Definition Language), commands such as CREATE is used to define the data.
DML (Data Manipulation Language), commands such are INSERT and DELETE are used to manipulate data.
DCL (Data Control Language), commands such is GRANT is used to control access to data.
Query (Retrieving data), is used to retrieve data using SELECT command.

2.2.3 PROCESSING …show more content…

For example: two departments contain their own system for their own data processing needs, where each of them stores data and runs all programs related to them. The biggest problem of decentralized data processing method is that: “data is to be duplicated”. Since common data is to be stored in each machine (redundancy), will cause data inconsistency. This means that data stored by two departments will not agree with each other (data will be duplicated), because there is no means to store common data in one place and access from all machines (Sharma, R.

Open Document