Ora Cursori PL SQL

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PBD Oracle Cursori expliciti-1

Copyright Oracle Corporation, 1998. All rights reserved.

2121

Writing Explicit CursorsWriting Explicit Cursors

21-2 Copyright Oracle Corporation, 1998. All rights reserved.

ObjectivesObjectives

After completing this lesson, you shouldbe able to do the following:

Distinguish between an implicit and an

explicit cursor

Use a PL/SQL record variable

Write a Cursor FOR loop

After completing this lesson, you shouldAfter completing this lesson, you should

be able to do the following:be able to do the following:

Distinguish between an implicit and an

explicit cursor

Use a PL/SQL record variable

Write a Cursor FOR loop


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About CursorsAbout Cursors

Every SQL statement executed by theOracle Server has an individual cursorassociated with it:

Implicit cursors: Declared for all DMLand PL/SQL SELECT statements.

Explicit cursors: Declared and named

by the programmer.

Every SQL statement executed by theEvery SQL statement executed by the

Oracle Server has an individual cursorOracle Server has an individual cursor

associated with it:associated with it:

Implicit cursors: Declared for all DMLand PL/SQL SELECT statements.

Explicit cursors: Declared and named

by the programmer.


Explicit Cursor FunctionsExplicit Cursor FunctionsExplicit Cursor Functions

Result SetResult 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 CursorsControlling Explicit CursorsControlling Explicit Cursors

Create aCreate anamednamed

SQL areaSQL area

DECLAREDECLAREDECLARE

IdentifyIdentifythe activethe active

setset

OPENOPENOPEN

Load theLoad thecurrentcurrent

row intorow into

variablesvariables

FETCHFETCHFETCH

Test forTest forexistingexisting

rowsrows

EMPTY?

Return toReturn toFETCH ifFETCH if

rowsrows

foundfound

NoNo

ReleaseReleasethe activethe active

setset

CLOSECLOSECLOSE

YesYes


Controlling Explicit CursorsControlling Explicit CursorsControlling Explicit CursorsOpen 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.

CursorCursor


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Declaring the CursorDeclaring the CursorDeclaring the CursorSyntax

Do not include the INTO clause in thecursor declaration.

If processing rows in a specificsequence is required use the ORDERBY clause in the query.

SyntaxSyntax

Do not include the INTO clause in thecursor declaration.

If processing rows in a specificsequence is required use the ORDERBY clause in the query.

CURSOR cursor_name IS

select_statement;

CURSOR cursor_name IS

select_statement;


Declaring the CursorDeclaring the CursorDeclaring the Cursor

ExampleExampleExample

DECLARECURSOR c1 ISSELECT empno, enameFROM emp;

CURSOR c2 ISSELECT *FROM deptWHERE deptno = 10;

BEGIN...


CURSOR c2 ISSELECT *FROM deptWHERE deptno = 10;

BEGIN...


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Opening the CursorOpening the CursorOpening the CursorSyntax

Open the cursor to execute the queryand identify the active set.

If the query returns no rows, noexception is raised.

Use cursor attributes to test theoutcome after a fetch.

SyntaxSyntax

Open the cursor to execute the queryand identify the active set.

If the query returns no rows, noexception is raised.

Use cursor attributes to test theoutcome after a fetch.

OPEN cursor_name;OPEN cursor_name;


Fetching Data from the CursorFetching Data from the CursorFetching Data from the Cursor

Syntax

Retrieve the current row values intooutput variables.

Include the same number of variables.

Match each variable to correspond tothe columns positionally.

Test to see if the cursor contains rows.

SyntaxSyntax

Retrieve the current row values intooutput variables.

Include the same number of variables.

Match each variable to correspond tothe columns positionally.

Test to see if the cursor contains rows.

FETCHcursor_name INTO [variable1, variable2, ...]

| record_name];

FETCHcursor_name INTO [variable1, variable2, ...]

| record_name];


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Fetching Data from the CursorFetching Data from the CursorFetching Data from the Cursor

ExamplesExamplesExamples

FETCH c1 INTO v_empno, v_ename;FETCH c1 INTO v_empno, v_ename;

...OPEN defined_cursor;LOOPFETCH defined_cursorINTO defined_variablesEXIT WHEN ...;

...-- Process the retrieved data

...END;

...OPEN defined_cursor;LOOPFETCH defined_cursorINTO defined_variablesEXIT WHEN ...;

...-- Process the retrieved data

...END;


Closing the CursorClosing the CursorClosing the Cursor

Syntax

Close the cursor after completing theprocessing of the rows.

Reopen the cursor, if required.

Do not attempt to fetch data from acursor once it has been closed.

SyntaxSyntax

Close the cursor after completing theprocessing of the rows.

Reopen the cursor, if required.

Do not attempt to fetch data from acursor once it has been closed.

CLOSE cursor_name;CLOSE cursor_name;


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Explicit Cursor AttributesExplicit Cursor AttributesExplicit Cursor AttributesObtain status information about a cursor.Obtain status information about a cursor.Obtain status information about 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 most

recent fetch returns a row;

complement of %NOTFOUND

%ROWCOUNT Number Evaluates to the total number of

rows returned so far


Controlling Multiple FetchesControlling Multiple Fetches

Process several rows from an explicitcursor using a loop.

Fetch a row with each iteration.

Use the %NOTFOUND attribute to writea test for an unsuccessful fetch.

Use explicit cursor attributes to test thesuccess of each fetch.

Process several rows from an explicitcursor using a loop.

Fetch a row with each iteration.

Use the %NOTFOUND attribute to writea test for an unsuccessful fetch.

Use explicit cursor attributes to test thesuccess of each fetch.


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

open.

Use the %ISOPEN cursor attributebefore performing a fetch to testwhether the cursor is open.

Example

Fetch rows only when the cursor isopen.

Use the %ISOPEN cursor attributebefore performing a fetch to testwhether the cursor is open.

ExampleExample

IF NOT c1%ISOPEN THEN

OPEN c1;END IF;

LOOP

FETCH c1...

IF NOT c1%ISOPEN THEN

OPEN c1;END IF;

LOOP

FETCH c1...


The %NOTFOUND and

%ROWCOUNT Attributes

The %NOTFOUND and

%ROWCOUNT Attributes

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

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

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

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


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Cursors and RecordsCursors and RecordsCursors and RecordsProcess the rows of the active setconveniently by fetching values into aPL/SQL RECORD.

Example

Process the rows of the active setProcess the rows of the active set

conveniently by fetching values into aconveniently by fetching values into a

PL/SQL RECORD.PL/SQL RECORD.

ExampleExample

...CURSOR c1 ISSELECT empno, enameFROM emp;

emp_record c1%ROWTYPE;

BEGINOPEN c1;

. . .FETCH c1 INTO emp_record;

...CURSOR c1 ISSELECT empno, enameFROM emp;

emp_record c1%ROWTYPE;

BEGINOPEN c1;

. . .FETCH c1 INTO emp_record;


Syntax

Shortcut to process explicit cursors.

Implicit open, fetch, and close occur.

Do not declare the record; it isimplicitly declared.

SyntaxSyntax

Shortcut to process explicit cursors.

Implicit open, fetch, and close occur.

Do not declare the record; it isimplicitly declared.

Cursor 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 LoopsRetrieve employees one by one until thereare no more left.

Example

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

ExampleExample


BEGINFOR emp_record IN c1 LOOP

-- implicit open and implicit fetch occurIF emp_record.empno = 7839 THEN...

END LOOP; -- implicit close occursEND;


BEGINFOR emp_record IN c1 LOOP




Cursor FOR Loops Using

Subqueries

Cursor FOR Loops Using

Subqueries

No Need to declare the cursor.

Example

No Need to declare the cursor.No Need to declare the cursor.

ExampleExample

BEGINFOR emp_record IN ( SELECT empno, enameFROM emp) LOOP



BEGIN

FOR emp_record IN ( SELECT empno, enameFROM emp) LOOP




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SummarySummary Cursor types:

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

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

Manipulate explicit cursors.

Evaluate the cursor status by usingcursor attributes.

Use cursor FOR loops.

Cursor types:

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

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

Manipulate explicit cursors.

Evaluate the cursor status by usingcursor attributes.

Use cursor FOR loops.


Practice OverviewPractice Overview

Declaring and using explicit cursors toquery rows of a table

Using a cursor FOR loop

Applying cursor attributes to test thecursor status

Declaring and using explicit cursors toquery rows of a table

Using a cursor FOR loop

Applying cursor attributes to test thecursor status


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