What does projection mean in Oracle?

Answer 1

Projection in Oracle is simply the fields (or columns) you wish to use when building a SELECT query. It is a subset of columns in a table. A projection is nothing but a named list of columns, which you can make use of in your application. Projections have no impact on business rules, they are purely for the use of the user interface. For example: SELECT title, author FROM books; In this case, "title" and "author" would be your projection.

Projection means to get data of particular columns in output instead of a whole row or record.

In other words, instead of listing values of all the columns for the records if we list values of only particular columns (and not all the columns) then it is known as projection.

Foe example:

Table Student

Roll_No Name Stream Marks

1 ABC Science 590

2. XYZ Commerce 450

Here, query for projection will be:

Select Roll_No, Name from Student ;

and Output will be:

Roll_No Name

1 ABC

2 XYZ

or

Example:

select roll_no where marks>400;

-------------------------------------------------------------------------

whereas the selection will be:

Select * from Student

or

Select * from Student where marks > 400

here all the rows and columns of the table will get printed depending on the condition given.