Oracle Certification - SQL Fundamentals I - Releational Theory

Introduction
Projection
Selection
Joining
Conclusion

Relational Theory

Relational Theory is branch of mathematics on which relational databases are based, and SQL is an interpretation of relational algebra. There are three sections to a SQL statement which concepts from this theory define, and which are always referred to in the OCP exams.

This is restricting the columns that are returned by the SELECT statement. The restriction of the returned columns is called projection. For example:

Note: Projection only means restricting the columns that are selected. For example using DISTINCT would not constitute projection.

Selection is the process of restricting the rows that are returned by a SELECT statement, i.e. the WHERE clause:

Joining relates tables to each other within a query, again in the WHERE clause:

Whilst these concepts don't exactly add much to my knowledge or Oracle and databases, they are part of the Oracle exam, and so they need committing to memory.

The next topic is going to be the venerable DESCRIBE command.

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