1. Chapter Eighteen Cursors
Chapter 18: Cursors
Chapter Eighteen Cursors
Objective:
Introduction to cursors
Use of cursors in a record variable
Implicit & explicit cursors
Cursors & loops
Cursors with parameters
COSC 641

2. Cursors DEF: A cursor is a pointer to the context area.
Context area: Memory location containing info needed to complete the PL/SQL processing
Chapter 18: Cursors

3. Cursors (Example) DECLARE V_ID Student.id%TYPE;
V_Name Student.name%TYPE;
V_Major Student.major%TYPE=‘COSC’;
CURSOR C_Student IS
SELECT id, name
FROM Student
WHERE major=V_Major;
BEGIN
OPEN C_Student;
LOOP FETCH C_Student INTO V_ID, V_Name;
EXIT WHEN C_Student%NOTFOUND;
END LOOP;
CLOSE C_Student;
END;
Chapter 18: Cursors

4. Cursors (Example 2) CURSOR My_cursor IS SELECT a.Name, b.Name, c.Name
FROM faculty a, student b, staff c
WHERE a.ID = b.ID AND
b.ID = c.ID;
Chapter 18: Cursors

5. Cursors
Every SQL statement is executed by the Oracle Server has a cursor associated with it.
Explicit cursors
Implicit cursors
Chapter 18: Cursors

6. Explicit Cursors Keep track of the current row that is processing
Active Set
1111
Mark
Cursor 
1231
Cathy
Current row
1421
Jack
1789
Sandy
Keep track of the current row that is processing
Process row by row
Programmer can manually control the cursor
All in an active set
Chapter 18: Cursors

7. Controlling Explicit Cursors:
Create a named SQL area; Declare the cursor
Identify the active set
Load the current row into variables
Test for existing rows
If found goto step 3
If not found goto step 5
Release the active set
Chapter 18: Cursors

8. Explicit Cursor Control retrieval of information: OPEN FETCH
How Many Rows
Close
Chapter 18: Cursors

9. Cursors (Example) DECLARE V_ID Student.id%TYPE;
V_Name Student.name%TYPE;
V_Major Student.major%TYPE=‘COSC’;
CURSOR C_Student IS
SELECT id, name
FROM Student
WHERE major=V_Major;
BEGIN
OPEN C_Student;
LOOP FETCH C_Student INTO V_ID, V_Name;
EXIT WHEN C_Student%NOTFOUND;
END LOOP;
CLOSE C_Student;
END;
Chapter 18: Cursors

10. Example CREATE OR REPLACE FUNCTION myFac(Name_In IN student.Name%TYPE)
RETURN NUMBER AS
CURSOR a IS
SELECT Major
FROM student
WHERE Name = UPPER(Name_In);
a_rec a%ROWTYPE;
Ret_val NUMBER;
BEGIN
OPEN a
FETCH a INTO a_rec;
If a%FOUND THEN
IF a_rec.Major = ‘COSC’ THEN
Ret_val = 10;
ELSEIF a_Rec.major = ‘MATH’ THEN
Ret_val = 5;
ENDIF
ENDIF;
CLOSE a;
RETURN Ret_Val;
END;
Chapter 18: Cursors

11. Controlling Explicit Cursors:
DECLARE
OPEN
FETCH
Test for empty rows
No: goto 3
Yes: goto 5
CLOSE
Chapter 18: Cursors

12. Declaring a Cursor Syntax: CURSOR C_Name [([Parameter [, parameter])]IS
Select_Statement [RETURN ret]
[For UPDATE [of [COLUMN List]];
Chapter 18: Cursors

13. Example IS CURSOR C_Faculty SELECT * FROM Faculty
WHERE Major=UPPER(‘COSC’);
 
CURSOR C_Dept
SELECT ID, No
FROM Dept
WHERE Name=UPPER(‘COSC’);
Chapter 18: Cursors

14. Example -----------------------------
CURSOR c_student (student_ID IN NUMBER) IS
SELECT Name
FROM student
WHERE student_ID = student.ID;
 
CURSOR staff_cur RETURN staff%ROWTYPE
SELECT *
FROM staff
WHERE dept = UPPER(‘COSC’);
Chapter 18: Cursors

15. Opening the Cursor Syntax OPEN C_Name;
OPEN is an executable statement that performs:
Dynamically allocates memory for a context area
Parses the SELECT statement
Binds the input variables: (obtain their memory address)
Identifies the active set
Positions the pointer just before the 1st row in the active set
Chapter 18: Cursors

16. Example DECLARE CURSOR C_Faculty IS CURSOR C_Dept IS
SELECT *
FROM F aculty
WHERE Major=‘COSC’;
CURSOR C_Dept IS
SELECT ID, No
FROM Dept
WHERE Name=‘COSC’;
V_F_Name Faculty.Name%TYPE;
V_F_Salary Faculty.Salary%TYPE;
V_D_Rec Dept%ROWTYPE;
BEGIN
OPEN C_Faculty;
OPEN C_Dept;
Chapter 18: Cursors

17. Fetching the Data Syntax: FETCH C_Name INTO [record_name| V1, V2, …];
Retrieve the current row values into output variables
Match each variable to the columns
Test to see if the cursor points to a row.
FETCH statement performs:
Advance the pointer to the next row in the active set
Reads the data from the current row into the output variables
Exit the loop, if the pointer points to the end of the active set
Chapter 18: Cursors

18. Example DECLARE CURSOR C_Faculty IS SELECT * FROM Faculty
WHERE Major=UPPER(‘COSC’);
CURSOR C_Dept IS
SELECT ID, No
FROM Dept
WHERE Name=‘COSC’;
V_F_Name Faculty.Name%TYPE;
V_F_Salary Faculty.Salary%TYPE;
V_D_Rec Dept%ROWTYPE;
BEGIN
OPEN C_Faculty;
OPEN C_Dept;
Chapter 18: Cursors

19. Example FOR I IN 1..5 LOOP FETCH C_Faculty INTO V_F_Name, V_F_Salary….
END LOOP;
LOOP
FETCH C_Dept INTO V_D_Rec
EXIT WHEN C_Dept%NOTFOUND
Chapter 18: Cursors

20. Closing the Cursor Syntax
CLOSE C_Name;
Close the cursor after the process is completed
Reopen the cursor, if it is needed
OPEN_CURSORS = 50
Chapter 18: Cursors

21. Cursor Attributes %FOUND Boolean Type %NOTFOUND Boolean Type
My_CUR%FOUND;
%NOTFOUND Boolean Type
My_CUR%NOTFOUND;
%ISOPEN Boolean Type
My_CUR%ISOPEN;
%ROWCOUNT Number Type
My_CUR%ROWCOUNT;
%BULK_ROWCOUNT
My_CUR% BULK_ROWCOUNT;
Chapter 18: Cursors

22. Cursor Exception INVALID_CURSOR TO)_MANY_ROWS %BULK_EXCEPTION
Chapter 18: Cursors

23. Example DECLARE Name Salary Mary 40,000 Mark 38,000 BEGIN END;
CURSOR C_Faculty IS
SELECT *
FROM Faculty;
V_F_Rec C_Faculty%ROWTYPE;
BEGIN
OPEN C_Faculty
FETCH C_Faculty INTO V_F_Rec;
CLOSE C_Faculty;
END;
Name Salary
Mary 40,000
Mark 38,000
Chapter 18: Cursors

24. %FOUND & %NOTFOUND C_Faculty%FOUND C_Faculty%NOTFOUND A: ORA_1001 B:
NULL C:
TRUE
FALSE D: E: F:
Chapter 18: Cursors

25. %ISOPEN & %ROWCOUNT C_Faculty%ISOPEN C_Faculty%ROWCOUNT A: FALSE
ORA_1001 B:
TRUE C: 1 D: 2 E: F:
Chapter 18: Cursors

26. Cursors with Parameters
Syntax
CURSOR C_Name [ (P1, P2, …) ] IS
Select_Statement;
Where P1,P2: P [IN] datatype [:=exp]
Pass parameter values to a cursor when the cursor is opened & the query is executed
Open an explicit cursor several times with a different active set each time.
Chapter 18: Cursors

27. Cursors with Parameters
Example:
DECLARE
CURSOR C_Student (V_ID NUMBER,
V_Major VARCHAR2) IS
SELECT ID, Major
FROM Student
WHERE Major = V_Major AND ID = V_ID;
BEGIN
OPEN C_Student (1111, ‘COSC’);
Chapter 18: Cursors

28. Cursors with Parameters
DECLARE
V_VAR_ID Student.ID%TYPE;
V_VAR_Major Student.Major%TYPE:=‘COSC’;
CURSOR C_Student (V_ID NUMBER,
V_Major VARCHAR2) IS
SELECT ….
OPEN C_Student (1111, V_VAR_Major);
OPEN C_Student (2222, ‘VART’);
Chapter 18: Cursors

29. Cursors with Parameters
CURSOR a (Name_IN VARCHAR2) IS
SELECT Major
FROM Student
WHERE Name = UPPER(Name_IN);
a_rec a%ROWTYPE;
ret_val NUMBER;
BEGIN
OPEN a (‘Major’);
FETCH a INTO a_Rec;
IF a%ROWTYPE THEN
IF a_Rec,Major = ‘COSC’ THEN
Ret_val = 10;
ELSEIf a_Rec.Major = ‘MATH’ THEN
Ret_val = 5;
ENDIF
ENDIF;
CLOSE a;
END;
Chapter 18: Cursors

30. Open Cursor with Parameters
OPEN a (:My_pack.Name);
OPEN a (‘John’);
OPEN a (‘Mark’);
Chapter 18: Cursors

31. FOR UPDATE Syntax SELECT ….. FROM ….. FOR UPDATE [OF Col_Ref] [NOWAIT]
Lock the record before update
Chapter 18: Cursors

32. Example DECLARE CURSOR C_Student IS SELECT * FROM Student
FOR UPDATE OF id, name;
Chapter 18: Cursors

33. Example DECLARE CURSOR C_Student IS SELECT Major, id FROM Student
WHERE Major = ‘COSC’
FOR UPDATE NOWAIT;
Chapter 18: Cursors

34. NO_DATA_FOUND VS. %NOTFOUND
SELECT ….
INTO …..
FROM …..
WHERE …..
NO_DATA_FOUND :Exception
%NOTFOUND :Flag
Chapter 18: Cursors

35. BULK COLLECT BC can retrieve multiple rows of data
Reduce Number of context switches between the PL/SQL & SQL
Reduce the overhead of data retrieval
Chapter 18: Cursors

36. BULK COLLECT DECLARE TYPE n IS TABLE OF Student.ID%TYPE;
TYPE m IS TABLE OF
Student.Major%TYPE;
a n;
b m;
CURSOR Temp IS
SELECT ID, Major
FROM Student
WHERE Dept=‘COSC’;
Chapter 18: Cursors

37. BULK COLLECT END; BEGIN Open Temp; FETCH Temp
BULK COLLECTION INTO a, b;
CLOSE Temp;
END;
Chapter 18: Cursors

38. BULK COLLECT DECLARE TYPE T_Number IS TABLE OF Temp_Table.ID%TYPE;
TYPE T_String IS TABLE OF
Temp_Table.Major%TYPE;
V_Num T_Number:=T_Number(1);
V_String T_String := T_String(1);
CURSOR Temp IS
SELECT Major
FROM Temp_Table
WHERE ID > 1111
ORDER BY ID;
Chapter 18: Cursors

39. BULK COLLECT END; BEGIN V_Number.EXTEND(1000); V_String.EXTEND(1000);
-- Load data into Temp_Table
SELECT ID, Major
FROM Temp_Table
BULK COLLECTION INTO V_Num, V_String
ORDER BY ID;
END;
Chapter 18: Cursors

40. Implicit Cursor INSERT DELETE UPDATE SELECT INTO DECLARE
a faculty%ROWTYPE;
BEGIN
SELECT *
INTO a
FROM faculty
WHERE ID = 1111;
END;
Chapter 18: Cursors

41. Error Handling with Implicit Cursor
NO_DATA_FOUND
TOO_MANY_ROWS
Chapter 18: Cursors

42. Implicit Cursor Attributes
SQL%FOUND
SQL%NOTFOUND
SQL%ROWCOUNT
SQL%ISOPEN --Always Return False
Chapter 18: Cursors

43. Implicit Cursor BEGIN UPDATE classroom SET NoOfSeats= 250
WHERE roomId=111;
IF SQL%NOTFOUND THEN
INSERT INTO classroom (roomId, NoOfSeats)
VALUES( 111, 250);
END IF;
Chapter 18: Cursors

44. Implicit Cursor BEGIN UPDATE classroom SET NoOfSeats= 250
WHERE roomId=111;
IF SQL%ROWCOUNT= 0 THEN
INSERT INTO classroom (roomId, NoOfSeats)
VALUES( 111, 250);
ENDIF;
Chapter 18: Cursors

45. Cursor Variable
CURSOR
CURSOR Variable
Chapter 18: Cursors

46. Cursor Variable TYPE ref_Type IS REF CURSOR [RETURN TYPE]; Example:
DECLARE
TYPE stud_type REF CURSOR RETURN student%ROWTYPE;
stud_cv stud_type; -- Declar Cursor Variable
TYPE fac_type REF CURSOR RETURN faculty%ROWTYPE;
fac_cv fac_type;
TYPE List IS TABLE of student%TYPE;
a List;
Chapter 18: Cursors

47. Controlling Cursor Variables
OPEN-FOR, FETCH, CLOSE
Example:
OPEN stud_cv FOR SELECT name, ID FROM Student;
FETCH stud_cv INTO a;
Chapter 18: Cursors

48. EXAMPLE
DECLARE
TYPE Company_Type IS REF CURSOR RETURN Company%ROWTYPE;
company_cv Company_Type;
company_Rec Company%ROWTYPE;
BEING
OPEN company_cv FOR
SELECT * FROM Company;
FETCH company_cv INTO company_Rec;
CLOSE company_cv;
END;
Chapter 18: Cursors