Sample Test #1 Questions

Transcription

1 Sample Test #1 Questions 1. Fibonacci numbers & Iteration Structures/using elsif a. Another program to generate Fibonacci numbers b. Makes use of the elsif selection structure c. It saves us of repeated use of end if d. It generates the sequence and accumulates it in a string (result) through concatenation e. The current program creates fib(20) f. result is the name of the string/varchar2(80) containing the sequence g. The repetition structure in this program is while loop end loop; h. put_line(result); displays the entire concatenated string once iterations are completed 1

2 2. in and out parameters (Sending & Receiving) a. in parameters makes debugging much easier b. The in parameter can be read but not updated c. The out parameter, on the other hand, is meant to be over-written d. If you try to update in parameter num in this program, it causes syntax error e. 999 is updated 55 and returned f. What happens to the 999 received by the procedure, before being updated to 55? g. Answer: It is an out parameter, it can only have return value (Declare num2 as in out number ) 2

3 3. Recursive Functions: Factorial Calaulation a. This procedure returns a number to the calling program b. This is a recursive procedure call (calling the procedure from within the procedure) c. So, it calls the procedure with 5, then 4, then 3, then 2, then 1, and finally 0 d. 0 corresponds to the base case which is evaluated as 1 e. Then 5*4*3*2*1*1 = 120 is returned as z in the calling procedure f. The results are then displayed outside the procedure g. Experimenting with factorial: 83! has 134 digits and 84! is beyond the limits of your computer 3

4 4. Another example of nested for loop end loop To count down from 10 to 1, for example: use for i in reverse loop 4

5 5. Arrays a. Array data type in PL/SQL is defined through: TYPE varray_type_name IS VARRAY(n) of <element_type> b. In the following program two arrays are declard: names of type namesarray and marks of type grade and then initialized c. The contents of these two arrays are the displayed on the screen d. Arrays in PL/SQL begin with index 1. 5

6 5. Cursors (write a cursor ) The cursor loads one tuple (row) into the context area, whereas the sql statement following PL/SQL program retrieves all tuples of the table. How would you retrieve all rows using the PL/SQL program? How about placing the fetch statement inside a loop, iterating till all tuples are counted for? Let s do it (see next page). 6

7 The following loop is much more efficient and does the same. 7

8 6. Implicit & Explicit Cursors: Additional Explicit Cursors Examples Using the employee table with 5 records, with empid, dept, salary, hiredate, supervisorid as attributes: a. Sample table employee before introducing the implicit cursors (sql%found and %notfound): b. The original table attributes (empid, dept, and salary) are renamed as e_id, e_dept, e_sal c. The cursor is declared as e_employee (still in DECLARE block) d. In the BEGIN block, the cursor is opened e. The rows are fetched one by one until the implicit cursor %notfound is true (no employees left) f. The loop ends after fetching 5 records and the cursor is closed g. Fetch goes forward, one row at a time, it cannot jump for row 1 to row 6, or go backward 8

9 7. ORDB Example: The mail-order database. 1. Step 1: create address_type object as follows: / 2. Step 2: create phones_varray_type as collection type, as follows: 3. Step 3: create person_type object as follows: 9

10 8. Declaring and Initializing Objects: Objects can be declared and used in PL/SQL based on object types defined in th edatabase. The structure of these objects can be traversed using the dot notation, objects can be modified and, if needed, the Database can be updated using the modified objects. In the following example, p is declared (and initialized) as a person_type object variable, which uses two already declared data types objects (address_type, and phones_varray_type). The following PL/SQL anonymous block creates a person_type object, initializes it, updates, updates its attributes, and calls a procedure to display the object. 10

11 9. Given the following table, write a trigger to show the old salary, new salary and the difference when the trigger is enabled in the database. 11

12 10. Test the trigger just defined in the previous question. Here are INSERT and UPDATE DML statements that fire the trigger. Make sure it is enabled. 12