Cursors (Cont.)

Below are explanations for the previous program (cont.):
Lines 013.- 18:
They are a PL/SQL loop. Notice that such a loop is bracketed by LOOP and END LOOP. Within the loop we find:

Line 013. LOOP
Start the loop.

Line 11: FETCH T1Cursor INTO a, b;
A fetch through the cursor into the local variables. In general, the FETCH statement must provide variables for each component of the tuple retrieved.

Line 13: EXIT WHEN T1Cursor%NOTFOUND;
A test for the loop-breaking condition. Its meaning should be clear: %NOTFOUND after the name of a cursor is true exactly when a fetch through that cursor has failed to find any more tuples.

Line 15: DELETE FROM T1 WHERE CURRENT OF T1Cursor;
An SQL DELETE statement that deletes the current tuple using the special WHERE condition CURRENT OF T1Cursor.

Line 17: INSERT INTO T1 VALUES( b, a );
An SQL INSERT statement that inserts the reverse tuple into T1.

Line 18: END LOOP;
End the loop.

Line 20: CLOSE T1Cursor;
Close the cursor.

Line 21: END;
End the PL/SQL program. 
DECLARE
  /* Output variables to hold the result of the query: */
  a  T1.e%type;
  b  T1.f%type;
  /* Cursor declaration: */
  CURSOR  T1Cursor  IS SELECT  e, f  FROM  T1  WHERE  e < f  FOR UPDATE;
BEGIN
  OPEN  T1Cursor;
  LOOP
    /* Retrieve each row of the result of the above query into PL/SQL variables: */
    FETCH  T1Cursor  INTO  a, b;
    /* If there are no more rows to fetch, exit the loop: */
    EXIT WHEN  T1Cursor%NOTFOUND;
    /* Delete the current tuple: */
    DELETE FROM  T1  WHERE CURRENT OF  T1Cursor;
    /* Insert the reverse tuple: */
    INSERT INTO  T1  VALUES( b, a );
  END LOOP;
  /* Free cursor used by the query. */
  CLOSE  T1Cursor;
END;




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