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CursorsCursorsCursorsCursors

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SQL CursorSQL CursorSQL CursorSQL Cursor A cursor is a private SQL work A cursor is a private SQL work

area.area. There are two types of cursors:There are two types of cursors:

Implicit cursorsImplicit cursors Explicit cursorsExplicit cursors

The Oracle Server uses implicit The Oracle Server uses implicit cursors to parse and execute your cursors to parse and execute your SQL statements.SQL statements.

Explicit cursors are explicitly Explicit cursors are explicitly declared by the programmer.declared by the programmer.

A cursor is a private SQL work A cursor is a private SQL work area.area.

There are two types of cursors:There are two types of cursors: Implicit cursorsImplicit cursors Explicit cursorsExplicit cursors

The Oracle Server uses implicit The Oracle Server uses implicit cursors to parse and execute your cursors to parse and execute your SQL statements.SQL statements.

Explicit cursors are explicitly Explicit cursors are explicitly declared by the programmer.declared by the programmer.

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CursorsCursors

Pointer to memory location on Pointer to memory location on database server database server DBMS uses to process a SQL queryDBMS uses to process a SQL query

Use to: Use to: Retrieve and manipulate database data Retrieve and manipulate database data

in PL/SQL programsin PL/SQL programs Types:Types:

ImplicitImplicit ExplicitExplicit

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Cursor

Context Area

active setCID CALLID CNAME CCREDIT

1 MIS 101 Intro. to Info. Sy stems 3 2 MIS 301 Sy stems Analy sis 3 3 MIS 441 Database Management 3 4 CS 155 Programming in C++ 3 5 MIS 451 Client/Serv er Sy stems 3

Number of rows

processed

Parsed commandstatement

Database Server Memory

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Implicit CursorsImplicit Cursors

Context areaContext area Contains information about queryContains information about query Created by INSERT, UPDATE, DELETE, Created by INSERT, UPDATE, DELETE,

or SELECTor SELECT Active setActive set

Set of data rows that query retrievesSet of data rows that query retrieves Implicit cursor Implicit cursor

Pointer to context areaPointer to context area

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Implicit Cursors Implicit Cursors (continued)(continued)

Use to assign output of SELECT Use to assign output of SELECT query to PL/SQL program variables query to PL/SQL program variables When query will return only one recordWhen query will return only one record

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Implicit Cursors Implicit Cursors (continued)(continued)

Useful to use %TYPE reference data Useful to use %TYPE reference data type type To declare variables used with implicit To declare variables used with implicit

cursorscursors Error “ORA-01422: exact fetch Error “ORA-01422: exact fetch

returns more than requested returns more than requested number of rows” number of rows” Implicit cursor query tried to retrieve Implicit cursor query tried to retrieve

multiple recordsmultiple records

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SQL Cursor AttributesSQL Cursor AttributesSQL Cursor AttributesSQL Cursor Attributes

Using SQL cursor attributes, you Using SQL cursor attributes, you can test the outcome of your can test the outcome of your SQL statements. SQL statements.

Using SQL cursor attributes, you Using SQL cursor attributes, you can test the outcome of your can test the outcome of your SQL statements. SQL statements. SQL%ROWCOUNT Number of rows affected by the

most recent SQL statement (an integer value)

SQL%FOUND Boolean attribute that evaluates to TRUE if the most recent SQL statement affects one or more rows

SQL%NOTFOUND Boolean attribute that evaluates to TRUE if the most recent SQLstatement does not affect any rows

SQL%ISOPEN Always evaluates to FALSE because PL/SQL closes implicit cursorsimmediately after they are executed

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SQL Cursor AttributesSQL Cursor AttributesSQL Cursor AttributesSQL Cursor Attributes Delete rows that have the Delete rows that have the

specified order number from the specified order number from the ITEM table. Print the number of ITEM table. Print the number of rows deleted.rows deleted.

ExampleExample

Delete rows that have the Delete rows that have the specified order number from the specified order number from the ITEM table. Print the number of ITEM table. Print the number of rows deleted.rows deleted.

ExampleExample VARIABLE rows_deleted VARCHAR2(30)DECLARE v_ordid NUMBER := 605;BEGIN DELETE FROM item WHERE ordid = v_ordid; :rows_deleted := (SQL%ROWCOUNT || ' rows deleted.');END;/PRINT rows_deleted

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Implicit Cursor SQLImplicit Cursor SQL%ROWCOUNT Example%ROWCOUNT Example

SQL> SET SERVEROUTPUT ON;SQL> SET SERVEROUTPUT ON;SQL> DECLARESQL> DECLARE r NUMBER;r NUMBER; BEGINBEGIN DELETE FROM emp WHERE DELETE FROM emp WHERE

empno=7900;empno=7900; r:=SQL%ROWCOUNT;r:=SQL%ROWCOUNT; DBMS_OUTPUT.PUT_LINE(r);DBMS_OUTPUT.PUT_LINE(r); END;END; //11

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Implicit Cursor SQLImplicit Cursor SQL%FOUND Example%FOUND Example

SQL> DECLARESQL> DECLARE r BOOLEAN;r BOOLEAN; BEGINBEGIN DELETE FROM emp WHERE empno=1000;DELETE FROM emp WHERE empno=1000; r:=SQL%FOUND;r:=SQL%FOUND; IF r THENIF r THEN DBMS_OUTPUT.PUT_LINE('Rows are founded');DBMS_OUTPUT.PUT_LINE('Rows are founded'); ELSEELSE DBMS_OUTPUT.PUT_LINE('No Rows are founded');DBMS_OUTPUT.PUT_LINE('No Rows are founded'); END IF;END IF; END;END; //No Rows are foundedNo Rows are founded

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Implicit Cursor SQLImplicit Cursor SQL%ISOPEN Example%ISOPEN Example

SQL> DECLARESQL> DECLARE r BOOLEAN;r BOOLEAN; BEGINBEGIN UPDATE emp SET sal=1000 WHERE empno>7900;UPDATE emp SET sal=1000 WHERE empno>7900; r:=SQL%ISOPEN;r:=SQL%ISOPEN; IF r THEN IF r THEN DBMS_OUTPUT.PUT_LINE('The cursor is opened');DBMS_OUTPUT.PUT_LINE('The cursor is opened'); ELSEELSE DBMS_OUTPUT.PUT_LINE('The cursor is closed');DBMS_OUTPUT.PUT_LINE('The cursor is closed'); END IF;END IF; END;END; //The cursor is closedThe cursor is closed

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About CursorsAbout CursorsAbout CursorsAbout Cursors

Every SQL statement Every SQL statement executed by the Oracle executed by the Oracle Server has an individual Server has an individual cursor associated with it:cursor associated with it: Implicit cursors: Declared for Implicit cursors: Declared for

all DML and PL/SQL SELECT all DML and PL/SQL SELECT statementsstatements

Explicit cursors: Declared and Explicit cursors: Declared and named by the programmernamed by the programmer

Every SQL statement Every SQL statement executed by the Oracle executed by the Oracle Server has an individual Server has an individual cursor associated with it:cursor associated with it: Implicit cursors: Declared for Implicit cursors: Declared for

all DML and PL/SQL SELECT all DML and PL/SQL SELECT statementsstatements

Explicit cursors: Declared and Explicit cursors: Declared and named by the programmernamed by the programmer

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Explicit Cursor FunctionsExplicit Cursor FunctionsExplicit Cursor FunctionsExplicit Cursor Functions

Active setActive set

Current rowCurrent rowCursor

7369 SMITH CLERK

7566 JONES MANAGER

7788 SCOTT ANALYST

7876 ADAMS CLERK

7902 FORD ANALYST

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Controlling Explicit Controlling Explicit CursorsCursors

Controlling Explicit Controlling Explicit CursorsCursors

• Create a Create a named named SQL areaSQL area

DECLAREDECLAREDECLAREDECLARE

• Identify Identify the active the active setset

OPENOPENOPENOPEN

• Load the Load the current current row into row into variablesvariables

FETCHFETCHFETCHFETCH

• Test for Test for existing existing rowsrows

EMPTY?

• Return to Return to FETCH if FETCH if rows rows foundfound

NoNo

• Release Release the active the active setset

CLOSECLOSECLOSECLOSEYesYes

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Controlling Explicit Controlling Explicit CursorsCursors

Controlling Explicit Controlling Explicit CursorsCursorsOpen the cursor.Open the cursor.

CursorCursor

PointerPointer

Fetch a row from the cursor.Fetch a row from the cursor.

CursorCursor

PointerPointer

Continue until empty.Continue until empty.

CursorCursor

PointerPointer

Close the cursor.Close the cursor.

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Declaring the CursorDeclaring the CursorDeclaring the CursorDeclaring the Cursor SyntaxSyntax

Do not include the INTO clause in the cursor Do not include the INTO clause in the cursor declaration.declaration.

If processing rows in a specific sequence is If processing rows in a specific sequence is required, use the ORDER BY clause in the query.required, use the ORDER BY clause in the query.

SyntaxSyntax

Do not include the INTO clause in the cursor Do not include the INTO clause in the cursor declaration.declaration.

If processing rows in a specific sequence is If processing rows in a specific sequence is required, use the ORDER BY clause in the query.required, use the ORDER BY clause in the query.

CURSOR cursor_name IS

select_statement;

CURSOR cursor_name IS

select_statement;

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Declaring the CursorDeclaring the CursorDeclaring the CursorDeclaring the Cursor

ExampleExample ExampleExampleDECLARE CURSOR emp_cursor IS SELECT empno, ename FROM emp;

CURSOR dept_cursor IS SELECT * FROM dept WHERE deptno = 10;BEGIN ...

DECLARE CURSOR emp_cursor IS SELECT empno, ename FROM emp;

CURSOR dept_cursor IS SELECT * FROM dept WHERE deptno = 10;BEGIN ...

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Opening the CursorOpening the CursorOpening the CursorOpening the Cursor

SyntaxSyntax

Open the cursor to execute the Open the cursor to execute the query and identify the active set.query and identify the active set.

If the query returns no rows, no If the query returns no rows, no exception is raised.exception is raised.

Use cursor attributes to test the Use cursor attributes to test the outcome after a fetch.outcome after a fetch.

SyntaxSyntax

Open the cursor to execute the Open the cursor to execute the query and identify the active set.query and identify the active set.

If the query returns no rows, no If the query returns no rows, no exception is raised.exception is raised.

Use cursor attributes to test the Use cursor attributes to test the outcome after a fetch.outcome after a fetch.

OPEN cursor_name;OPEN cursor_name;

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Fetching Data from the Fetching Data from the CursorCursor

Fetching Data from the Fetching Data from the CursorCursor SyntaxSyntax

Retrieve the current row values into Retrieve the current row values into variables.variables.

Include the same number of variables.Include the same number of variables. Match each variable to correspond to the Match each variable to correspond to the

columns positionally.columns positionally. Test to see if the cursor contains rows.Test to see if the cursor contains rows.

The FETCH statement performs the The FETCH statement performs the following operations:following operations:

1. Advances the pointer to the next row in the 1. Advances the pointer to the next row in the active set.active set.

2. Reads the data for the current row into the 2. Reads the data for the current row into the output PL/SQL variables.output PL/SQL variables.

SyntaxSyntax

Retrieve the current row values into Retrieve the current row values into variables.variables.

Include the same number of variables.Include the same number of variables. Match each variable to correspond to the Match each variable to correspond to the

columns positionally.columns positionally. Test to see if the cursor contains rows.Test to see if the cursor contains rows.

The FETCH statement performs the The FETCH statement performs the following operations:following operations:

1. Advances the pointer to the next row in the 1. Advances the pointer to the next row in the active set.active set.

2. Reads the data for the current row into the 2. Reads the data for the current row into the output PL/SQL variables.output PL/SQL variables.

FETCH cursor_name INTO [variable1, variable2, ...]

| record_name];

FETCH cursor_name INTO [variable1, variable2, ...]

| record_name];

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Fetching Data from the Fetching Data from the CursorCursor

Fetching Data from the Fetching Data from the CursorCursor

ExamplesExamples

ExamplesExamples

FETCH emp_cursor INTO v_empno, v_ename;FETCH emp_cursor INTO v_empno, v_ename;

...OPEN defined_cursor;LOOP FETCH defined_cursor INTO defined_variables EXIT WHEN ...; ... -- Process the retrieved data ...END;

...OPEN defined_cursor;LOOP FETCH defined_cursor INTO defined_variables EXIT WHEN ...; ... -- Process the retrieved data ...END;

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Closing the CursorClosing the CursorClosing the CursorClosing the Cursor

SyntaxSyntax

Close the cursor after completing Close the cursor after completing the processing of the rows.the processing of the rows.

Reopen the cursor, if required.Reopen the cursor, if required. Do not attempt to fetch data from a Do not attempt to fetch data from a

cursor once it has been closed.cursor once it has been closed. The CLOSE statement releases the context The CLOSE statement releases the context

area.area.

SyntaxSyntax

Close the cursor after completing Close the cursor after completing the processing of the rows.the processing of the rows.

Reopen the cursor, if required.Reopen the cursor, if required. Do not attempt to fetch data from a Do not attempt to fetch data from a

cursor once it has been closed.cursor once it has been closed. The CLOSE statement releases the context The CLOSE statement releases the context

area.area.

CLOSE cursor_name;CLOSE cursor_name;

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Explicit Cursor ExampleExplicit Cursor ExampleSQL> DECLARESQL> DECLARE v_num emp.empno%TYPE;v_num emp.empno%TYPE; v_name emp.ename%TYPE;v_name emp.ename%TYPE; CURSOR my_cursor IS SELECT empno,ename FROM emp CURSOR my_cursor IS SELECT empno,ename FROM emp

WHERE empno>7900;WHERE empno>7900; BEGINBEGIN OPEN my_cursor;OPEN my_cursor; LOOPLOOP FETCH my_cursor INTO v_num,v_name;FETCH my_cursor INTO v_num,v_name; EXIT WHEN my_cursor%NOTFOUND;EXIT WHEN my_cursor%NOTFOUND; DBMS_OUTPUT.PUT_LINE(v_num || ' has the name ' ||v_name);DBMS_OUTPUT.PUT_LINE(v_num || ' has the name ' ||v_name); END LOOP;END LOOP; CLOSE my_cursor;CLOSE my_cursor; END;END; //7902 has the name FORD7902 has the name FORD7934 has the name MILLER7934 has the name MILLER

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Explicit Cursor Explicit Cursor AttributesAttributes

Explicit Cursor Explicit Cursor AttributesAttributes Obtain status information about Obtain status information about

a cursor.a cursor.

Obtain status information about Obtain status information about a cursor.a cursor.Attribute Type Description

%ISOPEN Boolean Evaluates to TRUE if the cursor is open

%NOTFOUND Boolean Evaluates to TRUE if the most recent fetch does not return a row

%FOUND Boolean Evaluates to TRUE if the mostrecent fetch returns a row; complement of %NOTFOUND

%ROWCOUNT Number Evaluates to the total number of rows returned so far

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Controlling Multiple Controlling Multiple FetchesFetches

Controlling Multiple Controlling Multiple FetchesFetches

Process several rows from an Process several rows from an explicit cursor using a loop.explicit cursor using a loop.

Fetch a row with each iteration.Fetch a row with each iteration. Use the %NOTFOUND attribute to Use the %NOTFOUND attribute to

write a test for an unsuccessful write a test for an unsuccessful fetch.fetch.

Use explicit cursor attributes to Use explicit cursor attributes to test the success of each fetch.test the success of each fetch.

Process several rows from an Process several rows from an explicit cursor using a loop.explicit cursor using a loop.

Fetch a row with each iteration.Fetch a row with each iteration. Use the %NOTFOUND attribute to Use the %NOTFOUND attribute to

write a test for an unsuccessful write a test for an unsuccessful fetch.fetch.

Use explicit cursor attributes to Use explicit cursor attributes to test the success of each fetch.test the success of each fetch.

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The %ISOPEN AttributeThe %ISOPEN AttributeThe %ISOPEN AttributeThe %ISOPEN Attribute Fetch rows only when the cursor is Fetch rows only when the cursor is

open. open. Use the %ISOPEN cursor attribute Use the %ISOPEN cursor attribute

before performing a fetch to test before performing a fetch to test whether the cursor is open.whether the cursor is open.

ExampleExample

Fetch rows only when the cursor is Fetch rows only when the cursor is open. open.

Use the %ISOPEN cursor attribute Use the %ISOPEN cursor attribute before performing a fetch to test before performing a fetch to test whether the cursor is open.whether the cursor is open.

ExampleExampleIF NOT emp_cursor%ISOPEN THEN

OPEN emp_cursor;END IF;LOOP FETCH emp_cursor...

IF NOT emp_cursor%ISOPEN THENOPEN emp_cursor;

END IF;LOOP FETCH emp_cursor...

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The %NOTFOUND The %NOTFOUND and %ROWCOUNT and %ROWCOUNT

AttributesAttributes

The %NOTFOUND The %NOTFOUND and %ROWCOUNT and %ROWCOUNT

AttributesAttributes Use the %ROWCOUNT cursor Use the %ROWCOUNT cursor

attribute to retrieve an exact attribute to retrieve an exact number of rows.number of rows.

The value of %ROWCOUNT before The value of %ROWCOUNT before fetching any row is NULL.fetching any row is NULL.

Use the %NOTFOUND cursor Use the %NOTFOUND cursor attribute to determine when to exit attribute to determine when to exit the loop.the loop.

Use the %ROWCOUNT cursor Use the %ROWCOUNT cursor attribute to retrieve an exact attribute to retrieve an exact number of rows.number of rows.

The value of %ROWCOUNT before The value of %ROWCOUNT before fetching any row is NULL.fetching any row is NULL.

Use the %NOTFOUND cursor Use the %NOTFOUND cursor attribute to determine when to exit attribute to determine when to exit the loop.the loop.

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Explicit Cursor %ISOPEN Explicit Cursor %ISOPEN ExampleExample

SQL> DECLARESQL> DECLARE v_num emp.empno%TYPE;v_num emp.empno%TYPE; v_name emp.ename%TYPE;v_name emp.ename%TYPE; r BOOLEAN;r BOOLEAN; CURSOR my_cursor IS SELECT empno,ename FROM emp WHERE CURSOR my_cursor IS SELECT empno,ename FROM emp WHERE

empno>7900;empno>7900; BEGINBEGIN OPEN my_cursor;OPEN my_cursor; r:=my_cursor%ISOPEN;r:=my_cursor%ISOPEN; IF r THEN IF r THEN DBMS_OUTPUT.PUT_LINE('The Cursor is opened after the open DBMS_OUTPUT.PUT_LINE('The Cursor is opened after the open

statement');statement'); ELSEELSE DBMS_OUTPUT.PUT_LINE('The Cursor is closed after the open DBMS_OUTPUT.PUT_LINE('The Cursor is closed after the open

statement');statement'); END IF;END IF;

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Explicit Cursor %ISOPEN Explicit Cursor %ISOPEN Example Cont.Example Cont.

LOOPLOOP FETCH my_cursor INTO v_num,v_name;FETCH my_cursor INTO v_num,v_name; EXIT WHEN my_cursor%NOTFOUND;EXIT WHEN my_cursor%NOTFOUND; END LOOP;END LOOP; CLOSE my_cursor;CLOSE my_cursor; r:=my_cursor%ISOPEN;r:=my_cursor%ISOPEN; IF r THEN IF r THEN DBMS_OUTPUT.PUT_LINE('The Cursor is opened after the close DBMS_OUTPUT.PUT_LINE('The Cursor is opened after the close

statement');statement'); ELSEELSE DBMS_OUTPUT.PUT_LINE('The Cursor is closed after the close DBMS_OUTPUT.PUT_LINE('The Cursor is closed after the close

statement');statement'); END IF;END IF; END;END; //The Cursor is opened after the open statementThe Cursor is opened after the open statementThe Cursor is closed after the close statementThe Cursor is closed after the close statement

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Explicit Cursor Explicit Cursor %ROWCOUNT Example%ROWCOUNT Example

SQL> DECLARESQL> DECLARE v_name emp.ename%TYPE;v_name emp.ename%TYPE; r NUMBER;r NUMBER; c NUMBER:=1;c NUMBER:=1; CURSOR my_cursor IS SELECT ename FROM emp WHERE empno>7900;CURSOR my_cursor IS SELECT ename FROM emp WHERE empno>7900; BEGINBEGIN OPEN my_cursor;OPEN my_cursor; LOOPLOOP FETCH my_cursor INTO v_name;FETCH my_cursor INTO v_name; EXIT WHEN my_cursor%NOTFOUND;EXIT WHEN my_cursor%NOTFOUND; r:=my_cursor%ROWCOUNT;r:=my_cursor%ROWCOUNT; DBMS_OUTPUT.PUT_LINE('After fetch number ' || c || ' ROWCOUNT has the value ' || DBMS_OUTPUT.PUT_LINE('After fetch number ' || c || ' ROWCOUNT has the value ' ||

r);r); c:=c+1;c:=c+1; END LOOP;END LOOP; CLOSE my_cursor;CLOSE my_cursor; END;END; //After fetch number 1 ROWCOUNT has the value 1After fetch number 1 ROWCOUNT has the value 1After fetch number 2 ROWCOUNT has the value 2After fetch number 2 ROWCOUNT has the value 2

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Cursors and RecordsCursors and RecordsCursors and RecordsCursors and Records Process the rows of the active Process the rows of the active

set conveniently by fetching set conveniently by fetching values into a PL/SQL RECORD.values into a PL/SQL RECORD.

ExampleExample

Process the rows of the active Process the rows of the active set conveniently by fetching set conveniently by fetching values into a PL/SQL RECORD.values into a PL/SQL RECORD.

ExampleExampleDECLARE CURSOR emp_cursor IS SELECT empno, ename FROM emp; emp_record emp_cursor%ROWTYPE;BEGIN OPEN emp_cursor; LOOP FETCH emp_cursor INTO emp_record; ...

DECLARE CURSOR emp_cursor IS SELECT empno, ename FROM emp; emp_record emp_cursor%ROWTYPE;BEGIN OPEN emp_cursor; LOOP FETCH emp_cursor INTO emp_record; ...

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SyntaxSyntax

The cursor FOR loop is a shortcut to The cursor FOR loop is a shortcut to process explicit cursors.process explicit cursors.

Implicit open, fetch, and close occur.Implicit open, fetch, and close occur. The record is implicitly declared.The record is implicitly declared.

SyntaxSyntax

The cursor FOR loop is a shortcut to The cursor FOR loop is a shortcut to process explicit cursors.process explicit cursors.

Implicit open, fetch, and close occur.Implicit open, fetch, and close occur. The record is implicitly declared.The record is implicitly declared.

Cursor FOR LoopsCursor FOR LoopsCursor FOR LoopsCursor FOR Loops

FOR record_name IN cursor_name LOOP

statement1;

statement2;

. . .

END LOOP;

FOR record_name IN cursor_name LOOP

statement1;

statement2;

. . .

END LOOP;

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Cursor FOR LoopsCursor FOR LoopsCursor FOR LoopsCursor FOR Loops

Retrieve employees one by one Retrieve employees one by one until no more are left.until no more are left.

ExampleExample

Retrieve employees one by one Retrieve employees one by one until no more are left.until no more are left.

ExampleExampleDECLARE CURSOR emp_cursor IS SELECT ename, deptno FROM emp;BEGIN FOR emp_record IN emp_cursor LOOP -- implicit open and implicit fetch occur IF emp_record.deptno = 30 THEN ... END LOOP; -- implicit close occursEND;

DECLARE CURSOR emp_cursor IS SELECT ename, deptno FROM emp;BEGIN FOR emp_record IN emp_cursor LOOP -- implicit open and implicit fetch occur IF emp_record.deptno = 30 THEN ... END LOOP; -- implicit close occursEND;

SummarySummarySummarySummary Cursor types:Cursor types:

Implicit cursors: Used for all DML Implicit cursors: Used for all DML statements and single-row queries.statements and single-row queries.

Explicit cursors: Used for queries of Explicit cursors: Used for queries of zero, one, or more rows.zero, one, or more rows.

You can manipulate explicit cursors.You can manipulate explicit cursors. You can evaluate the cursor status You can evaluate the cursor status

by using cursor attributes.by using cursor attributes. You can use cursor FOR loops.You can use cursor FOR loops.

Cursor types:Cursor types: Implicit cursors: Used for all DML Implicit cursors: Used for all DML

statements and single-row queries.statements and single-row queries. Explicit cursors: Used for queries of Explicit cursors: Used for queries of

zero, one, or more rows.zero, one, or more rows. You can manipulate explicit cursors.You can manipulate explicit cursors. You can evaluate the cursor status You can evaluate the cursor status

by using cursor attributes.by using cursor attributes. You can use cursor FOR loops.You can use cursor FOR loops.