Opening a cursor variable, PL-SQL Programming

Assignment Help:

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;


Related Discussions:- Opening a cursor variable

Autonomous versus nested transactions, Autonomous versus Nested Transaction...

Autonomous versus Nested Transactions Though an autonomous transaction is started by the other transaction, it is not a nested transaction for the reasons shown below: (i)

Tables within a table - sql, Tables within a Table - SQL Figure here ...

Tables within a Table - SQL Figure here is an exact copy of the one in the theory book and as before it is just an alternative way of representing some of the information con

Using forall and bulk collect - bulk bind performance, Using FORALL and BUL...

Using FORALL and BULK COLLECT Together You can unite the BULK COLLECT clause with the FORALL statement, in that case, the SQL engine bulk-binds column values incrementally. In

Parameter and keyword description - insert statement, Parameter and Keyword...

Parameter and Keyword Description:   table_reference: This identifies a table or view which should be available when you execute the INSERT statement, and for that you sho

Oracle development , Write a stored procedure that accepts the post code in...

Write a stored procedure that accepts the post code in which the customer resides as the input parameter. The procedure should then use an explicit cursor to display comprehensive

Redeclaring predefined exceptions - user-defined exceptions, Redeclaring Pr...

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.

Data types in sql, Data Types in SQL SQL's concept does not differ sig...

Data Types in SQL SQL's concept does not differ significantly from that defined in the theory book, apart from that business concerning NULL. However, the theory book equates

Using default-declarations in sql, Using DEFAULT You can use the keyword...

Using DEFAULT You can use the keyword DEFAULT rather than that of the assignment operator to initialize the variables. For e.g. the declaration blood_type CHAR := ’O’; it can b

How transactions guard your database, How Transactions Guard Your Database ...

How Transactions Guard Your Database The transaction is a sequence of SQL data manipulation statements which does a logical unit of work. The Oracle treats the sequence of SQL

Develop data business intelligence project, Develop Data Business Intellige...

Develop Data Business Intelligence Project Project Description: We are linking our Microsoft SQL Database to GoodData Business Intelligence. We are seeking somebody who has e

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd