#Distributed database management system pdf how to#
But the present problem is many of the software developers, specialists, programmers, and researchers are not aware of how to represent queries exactly in that syntax. After understanding the basics of all SQL joins, then it is necessary to represent the same queries in relational algebraic notations, because, those are the standard and uniform syntaxes which will be applicable in any of the database software. The number of records used in these tables is very minimum and are meaningful records. To avoid all these uncertainties, confusion, ambiguities, in this paper, it has been used with only three simple tables which are given from Oracle Corporation in user schema scott/tiger. Since the present tables are dealing with millions of records, if we take these tables as example tables, then it is very difficult to give the exact demonstration regarding the number of records to be accessed, because, many joining concepts dealing with exact number of records which are working based on Cartesian Product.
This is due to lack of knowledge of the programmers on evaluation criteria of the joined queries. Even if we use some conventional operators, the performance of the query may results in delayed accessing time in retrieving the data from N number of tables. Sometimes it is vey difficult for the teacher or trainer to convince the trainees, students, research scholars in giving right practical examples while we teach SQL joins to them. The problem presently we are facing is many of them are not knowing exactly all types of joins, their proper syntaxes and their proper usage. For this purpose, generally we are using relational operators along with logical operators. In join processes, the accessing of the data depends on the joining conditions with different operators. It all depends on the format in which we need to display the data in the user environment. Sometimes join is required even if there is a single table. Whenever we need the data which is not available from a single table, then it needs to necessitate using join operation.
Join is an operation in accessing the data from table if number of tables exceeds one.