Opening a cursor variable, PL-SQL Programming

Opening a Cursor Variable

The OPEN-FOR statement relates a cursor variable with the multi-row query, executes the query, and then identifies the result set. The syntax for opening a cursor is as shown below:

OPEN {cursor_variable_name | :host_cursor_variable_name}

FOR select_statement;

Where the host_cursor_variable_name identify the cursor variable declared in the PL/SQL host environments like an OCI or Pro C program.

Dissimilar cursors, the cursor variables take no parameters. Though, no flexibility is lost as you can pass entire queries (not just parameters) to the cursor variable. The query can reference the host variables and the PL/SQL parameters, functions, and variables but cannot be FOR UPDATE. In the illustration below, you open the cursor variable emp_cv. Note that you can apply the cursor attributes (%ISOPEN, %FOUND, %NOTFOUND, and %ROWCOUNT) to the cursor variable.

IF NOT emp_cv%ISOPEN THEN

/* Open cursor variable. */

OPEN emp_cv FOR SELECT * FROM emp;

END IF;

The Other OPEN-FOR statements can open similar cursor variable for various queries. You do not require closing a cursor variable before reopening it.  Whenever you reopen a cursor variable for various queries, the earlier query is lost.

Usually, you open the cursor variable by passing it to the stored procedure which declares a cursor variable as one of its formal parameters. For illustration, the packaged procedure below opens the cursor variable emp_cv:

CREATE PACKAGE emp_data AS

...

TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE;

PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp);

END emp_data;

CREATE PACKAGE BODY emp_data AS

...

PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp) IS

BEGIN

OPEN emp_cv FOR SELECT * FROM emp;

END open_emp_cv;

END emp_data;

Whenever you declare a cursor variable as the formal parameter of a subprogram which opens the cursor variable, you should specify the IN OUT mode. In the similar way, the subprogram can pass an open cursor back to the caller.

Or else, you can use a stand-alone process to open the cursor variable. Basically define the REF CURSOR type in the separate package, and then reference that type in the stand-alone process. For illustration, if you create the following bodiless package, you can make stand-alone process that references the types it defines:

CREATE PACKAGE cv_types AS

TYPE GenericCurTyp IS REF CURSOR;

TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE;

TYPE DeptCurTyp IS REF CURSOR RETURN dept%ROWTYPE;

...

END cv_types;

In the next illustration, you create a stand-alone process which references the REF CURSOR type EmpCurTyp that is defined in the package cv_types:

CREATE PROCEDURE open_emp_cv (emp_cv IN OUT cv_types.EmpCurTyp) AS

BEGIN

OPEN emp_cv FOR SELECT * FROM emp;

END open_emp_cv;

To integrate the data retrieval, you can group the type-compatible queries in a stored procedure. In the illustration below, the packaged procedure declare a selector as one of its formal parameters. (In this framework, the selector is a variable used to select one of few alternatives in a conditional control statement.) Whenever called, the procedure opens the cursor variable emp_cv for the chosen query.

CREATE PACKAGE emp_data AS

TYPE GenericCurTyp IS REF CURSOR;

TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE;

PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp, choice NUMBER);

END emp_data;

CREATE PACKAGE BODY emp_data AS

PROCEDURE open_emp_cv (

emp_cv IN OUT EmpCurTyp,

choice NUMBER) IS

BEGIN

IF choice = 1 THEN

OPEN emp_cv FOR SELECT * FROM emp WHERE comm IS NOT NULL;

ELSIF choice = 2 THEN

OPEN emp_cv FOR SELECT * FROM emp WHERE sal > 2500;

ELSIF choice = 3 THEN

OPEN emp_cv FOR SELECT * FROM emp WHERE deptno = 20;

END IF;

END open_emp_cv;

END emp_data;

For additional flexibility, you can pass a cursor variable & a selector to the stored procedure which executes queries with various return types. Consider this illustration as shown:

CREATE PACKAGE BODY emp_data AS

PROCEDURE open_cv (

generic_cv IN OUT GenericCurTyp,

choice NUMBER) IS

BEGIN

IF choice = 1 THEN

OPEN generic_cv FOR SELECT * FROM emp;

ELSIF choice = 2 THEN

OPEN generic_cv FOR SELECT * FROM dept;

ELSIF choice = 3 THEN

OPEN generic_cv FOR SELECT * FROM salgrade;

END IF;

END open_cv;

END emp_data;

Posted Date: 10/4/2012 4:02:57 AM | Location : United States







Related Discussions:- Opening a cursor variable, Assignment Help, Ask Question on Opening a cursor variable, Get Answer, Expert's Help, Opening a cursor variable Discussions

Write discussion on Opening a cursor variable
Your posts are moderated
Related Questions
Explicit Cursors The set of rows returned by the query can include zero, one, or multiple rows, depending on how many rows meet your search criteria. Whenever a query returns

Using Operator DEREF: You cannot navigate through refs within the PL/SQL procedural statements. Rather than, you should use the operator DEREF in the SQL statement. The DEREF

Write a cursor to open an employee database and fetch the employee record whose age is greater than 45

Case Sensitivity Similar to all the identifiers, the variables, the names of constants, and parameters are not case sensitive. For illustration, PL/SQL considers the following n

Cursor Variables Similar to a cursor, cursor variable points to the current row in the result set of a multi-row query. But, dissimilar a cursor, a cursor variable can be opene

Parameter and Keyword Description: cursor_name: This identifies an explicit cursor formerly declared within the present scope. cursor_variable_name: These identif

Using DELETE This process has three forms. The DELETE removes all elements from the collection. DELETE(n) removes the nth element from the nested table. When n is null, then D

MAX and MIN operator in SQL Example: (SELECT MAX (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') (SELECT MIN (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') Example

Parameter and Keyword Description: EXIT: An unconditional EXIT statement (i.e., one without a WHEN clause) exits the present loop instantly. The Execution resumes with th

Redeclaring Predefined Exceptions Keep in mind that, the PL/SQL declares predefined exceptions globally in the package STANDARD; Therefore you need not declare them yourself.