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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Error Handling with Implicit Cursor NO_DATA_FOUND TOO_MANY_ROWS Chapter 18: Cursors

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

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

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

Cursor Variable CURSOR CURSOR Variable Chapter 18: Cursors

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

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

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