2 types of cursors .

•   Implicit Cursor.
•   Explicit Cursor.

Implicit cursor: Oracle will implicitly creates an area for the DML operations.

Explicit cursors :are created by the programmer.

Restrictions on Cursor Variables

• cannot assign NULL
• cursor's values cannot be stored in table columns
• cannot be used with associative array, nested tables and varray
• cannot be use one where the other is expected
• cannot reference a cursor variable in cursor FOR LOOP
• cannot direclty goto any columns
•  u cannot declare cursor in package specification
• not allowed when using db links

ref cursor

Its a run time query binding with the cursor variable.
Ref cursors are 2 types
 

• 1. weak Ref cursor
• 2. Strong Ref cursor