Basics of Tables

Concepts in 18 C:

Let see about tables.

In a relational database tables play a vital part to organize data and regularize it as per size and requirement.

Let’s see about permanent tables, temporary tables, external tables, heap organized tables, index-organized tables.

You can define table into two categories: Relational and object tables:

Relational tables are simple and common tables. For example, recording list of students, employees etc. No need to look for dependencies while creating.

Object type tables are table with reference to the application it is related to. The table will be designed for a purpose and also validating or summarizing the dependence’s.

Relational Tables:

S.no	Emp Name	Emp ID	Dept ID
1	a	12	0001
2	b	23	0002

Object Type:

Test	Maths	Science	English	Total
1	100	100	100	300
2	100	100	100	300

create type stud as object (
          maths number(3),
          phy   number(3),
          chem  number(3),
          member function tot return number);

functions can be called inside the object type column.

Ok, Let’s see about table structures:

 heap-organized table :Stores data where ever the storage is available. As normal as our own table at office. Place the things as we go.

index-organized table: Stores data with its primary key as key reference for sequential ordering of storing of data. Or by using pseudocolumn to be referenced to sequence data. Index is not a separate column which points to the data. Instead works as organized data which is sequential and easy to identify in the order we arrange it.

Temporary table:  for a particular session and only be accessed by its owner. While the session gets completed the data will be erased.

 External table: is a read-only table whose metadata is stored in the database but whose data is stored outside the database. For example, the text file needs to be loaded in ETL from a other database and which creates a virtual column in our database while loading.