What is the usage of the cursor in Oracle?

In Oracle databases, a cursor is a database object used for handling query result sets. Cursors allow developers to traverse and manipulate the query result sets.

The main purpose of a cursor in PL/SQL is to manage multiple rows in a query result set. By using a cursor, you can store the query result set in memory, locate specific rows using the cursor, and process the results line by line.

The usage of the cursor is as follows:

1. Declare cursor: Use the DECLARE statement to declare a cursor and specify the query statement. For example:

DECLARE
   cursor_name CURSOR FOR SELECT column1, column2 FROM table_name;

1. Open the cursor: Use the OPEN statement to open the cursor, enabling it to be used. For example:

OPEN cursor_name;

1. Retrieve cursor data: Use the FETCH statement to retrieve the current row data of the cursor. Different FETCH statements can be used to retrieve different rows or retrieve multiple rows at once. For example:

FETCH cursor_name INTO variable1, variable2;

1. Process cursor data: Perform appropriate operations on the retrieved data, such as outputting, calculating, etc.
2. Close the cursor: Use the CLOSE statement to close the cursor and release any related resources. For example:

CLOSE cursor_name;

1. Release cursor: Use the DEALLOCATE statement to free the memory occupied by the cursor. For example:

DEALLOCATE cursor_name;

Cursors can also be utilized for traversing result sets through related loop structures such as WHILE or FOR. By using cursors, it becomes efficient to handle and manipulate an abundance of query result data.