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OPEN Statement

OPEN Statement

The OPEN statement executes the query associated with a cursor. It allocates database resources to process the query and identifies the result set -- the rows that match the query conditions. The cursor is positioned before the first row in the result set. For more information, see "Querying Data with PL/SQL" on page 6-9.

Syntax

open_statement

,

 

 

(

cursor_parameter_name

)

OPEN

cursor_name

 

;

Keyword and Parameter Description

cursor_name

An explicit cursor previously declared within the current scope and not currently open.

cursor_parameter_name

A variable declared as the formal parameter of a cursor. (For the syntax of cursor_parameter_declaration, see "Cursors" on page 13-38.) A cursor parameter can appear in a query wherever a constant can appear.

Usage Notes

Generally, PL/SQL parses an explicit cursor only the first time it is opened and parses a SQL statement (creating an implicit cursor) only the first time the statement is executed. All the parsed SQL statements are cached. A SQL statement is reparsed only if it is aged out of the cache by a new SQL statement. Although you must close a cursor before you can reopen it, PL/SQL need not reparse the associated SELECT statement. If you close, then immediately reopen the cursor, a reparse is definitely not needed.

Rows in the result set are not retrieved when the OPEN statement is executed. The FETCH statement retrieves the rows. With a FOR UPDATE cursor, the rows are locked when the cursor is opened.

If formal parameters are declared, actual parameters must be passed to the cursor. The formal parameters of a cursor must be IN parameters; they cannot return values to actual parameters. The values of actual parameters are used when the cursor is opened. The datatypes of the formal and actual parameters must be compatible. The query can also reference PL/SQL variables declared within its scope.

Unless you want to accept default values, each formal parameter in the cursor declaration must have a corresponding actual parameter in the OPEN statement. Formal parameters declared with a default value do not need a corresponding actual parameter. They assume their default values when the OPEN statement is executed.

You can associate the actual parameters in an OPEN statement with the formal parameters in a cursor declaration using positional or named notation.

If a cursor is currently open, you cannot use its name in a cursor FOR loop.

PL/SQL Language Elements 13-93

OPEN Statement

Examples

Given the cursor declaration:

CURSOR parts_cur IS SELECT part_num, part_price FROM parts;

the following statement opens the cursor:

OPEN parts_cur;

Given the cursor declaration:

CURSOR emp_cur(my_ename VARCHAR2, my_comm NUMBER DEFAULT 0)

IS SELECT * FROM emp WHERE ...

any of the following statements opens the cursor:

OPEN emp_cur('LEE');

OPEN emp_cur('BLAKE', 300);

OPEN emp_cur(employee_name, 150);

Related Topics

CLOSE Statement, Cursors, FETCH Statement, LOOP Statements

13-94 PL/SQL User's Guide and Reference

OPEN-FOR Statement

OPEN-FOR Statement

The OPEN-FOR statement executes the query associated with a cursor variable. It allocates database resources to process the query and identifies the result set -- the rows that meet the query conditions. The cursor variable is positioned before the first row in the result set. For more information, see "Using Cursor Variables (REF CURSORs)" on page 6-19.

Syntax

open_for_statement

 

 

 

cursor_variable_name

 

 

OPEN

FOR

select_statement

;

:

host_cursor_variable_name

 

 

Keyword and Parameter Description

cursor_variable_name

A cursor variable (or parameter) previously declared within the current scope.

host_cursor_variable_name

A cursor variable previously declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. The datatype of the host cursor variable is compatible with the return type of any PL/SQL cursor variable. Host variables must be prefixed with a colon.

select_statement

A query associated with cursor_variable, which returns a set of values. The query can reference bind variables and PL/SQL variables, parameters, and functions. The syntax of select_statement is similar to the syntax for select_into_statement defined in "SELECT INTO Statement" on page 13-123, except that the cursor select_statement cannot have an INTO clause.

Usage Notes

You can declare a cursor variable in a PL/SQL host environment such as an OCI or Pro*C program. To open the host cursor variable, you can pass it as a bind variable to an anonymous PL/SQL block. You can reduce network traffic by grouping OPEN-FOR statements. For example, the following PL/SQL block opens five cursor variables in a single round-trip:

/* anonymous PL/SQL block in host environment */ BEGIN

OPEN :emp_cv FOR SELECT * FROM emp; OPEN :dept_cv FOR SELECT * FROM dept;

OPEN :grade_cv FOR SELECT * FROM salgrade; OPEN :pay_cv FOR SELECT * FROM payroll; OPEN :ins_cv FOR SELECT * FROM insurance;

END;

Other OPEN-FOR statements can open the same cursor variable for different queries. You do not need to close a cursor variable before reopening it. When you reopen a cursor variable for a different query, the previous query is lost.

PL/SQL Language Elements 13-95

OPEN-FOR Statement

Unlike cursors, cursor variables do not take parameters. Instead, you can pass whole queries (not just parameters) to a cursor variable.

Although a PL/SQL stored procedure or function can open a cursor variable and pass it back to a calling subprogram, the calling and called subprograms must be in the same instance. You cannot pass or return cursor variables to procedures and functions called through database links.

When you declare a cursor variable as the formal parameter of a subprogram that opens the cursor variable, you must specify the IN OUT mode. That way, the subprogram can pass an open cursor back to the caller.

Examples

To centralize data retrieval, you can group type-compatible queries in a stored procedure. When called, the following packaged procedure opens the cursor variable emp_cv for the chosen query:

CREATE PACKAGE emp_data AS

TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE;

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

END emp_data;

CREATE PACKAGE BODY emp_data AS

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

END emp_data;

For more flexibility, you can pass a cursor variable and a selector to a stored procedure that executes queries with different return types:

CREATE PACKAGE admin_data AS

TYPE GenCurTyp IS REF CURSOR;

PROCEDURE open_cv (generic_cv IN OUT GenCurTyp, choice INT);

END admin_data;

CREATE PACKAGE BODY admin_data AS

PROCEDURE open_cv (generic_cv IN OUT GenCurTyp, choice INT) 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;

END admin_data;

Related Topics

CLOSE Statement, Cursor Variables, FETCH Statement, LOOP Statements

13-96 PL/SQL User's Guide and Reference

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