What is the difference between explicit and implicit cursors in Oracle?

Question

I am a bit rusty on my cursor lingo in PL/SQL. Anyone know this?

Answer 1

From a performance point of view, Implicit cursors are faster.

Let's compare the performance between an explicit and implicit cursor:

SQL> DECLARE
  2    l_loops  NUMBER := 100000;
  3    l_dummy  dual.dummy%TYPE;
  4    l_start  NUMBER;
  5    -- explicit cursor declaration
  6    CURSOR c_dual IS
  7      SELECT dummy
  8      FROM   dual;
  9  BEGIN
 10    l_start := DBMS_UTILITY.get_time;
 11    -- explicitly open, fetch and close the cursor
 12    FOR i IN 1 .. l_loops LOOP
 13      OPEN  c_dual;
 14      FETCH c_dual
 15      INTO  l_dummy;
 16      CLOSE c_dual;
 17    END LOOP;
 18
 19    DBMS_OUTPUT.put_line('Explicit: ' ||
 20                         (DBMS_UTILITY.get_time - l_start) || ' hsecs');
 21
 22    l_start := DBMS_UTILITY.get_time;
 23    -- implicit cursor for loop
 24    FOR i IN 1 .. l_loops LOOP
 25      SELECT dummy
 26      INTO   l_dummy
 27      FROM   dual;
 28    END LOOP;
 29
 30    DBMS_OUTPUT.put_line('Implicit: ' ||
 31                         (DBMS_UTILITY.get_time - l_start) || ' hsecs');
 32  END;
 33  /
Explicit: 332 hsecs
Implicit: 176 hsecs

PL/SQL procedure successfully completed.

So, a significant difference is clearly visible. Implicit cursor is much faster than an explicit cursor.

More examples here.