plsql les06

6
Dynamic SQL and Metadata

Copyright © 2004, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to do
the following:
• Describe the execution flow of SQL statements
• Build and execute SQL statements dynamically
using Native Dynamic SQL (that is, with EXECUTE
IMMEDIATE statements)
• Compare Native Dynamic SQL with the DBMS_SQL
package approach
• Use the DBMS_METADATA package to obtain
metadata from the data dictionary as XML or
creation DDL that can be used to re-create the
objects

6-2 Copyright © 2004, Oracle. All rights reserved.

Execution Flow of SQL

• All SQL statements go through various stages:
– Parse
– Bind
– Execute
– Fetch
• Some stages may not be relevant for all
statements—for example, the fetch phase is
applicable to queries.
Note: For embedded SQL statements (SELECT, DML,
COMMIT and ROLLBACK), the parse and bind phases are
done at compile time. For dynamic SQL statements, all
phases are performed at run time.


Dynamic SQL

Use dynamic SQL to create a SQL statement whose
structure may change during run time. Dynamic SQL:
• Is constructed and stored as a character string
within the application
• Is a SQL statement with varying column data, or
different conditions with or without placeholders
(bind variables)
• Enables data-definition, data-control, or session-
control statements to be written and executed
from PL/SQL
• Is executed with Native Dynamic SQL statements
or the DBMS_SQL package


Native Dynamic SQL

• Provides native support for dynamic SQL directly
in the PL/SQL language
• Provides the ability to execute SQL statements
whose structure is unknown until execution time
• Is supported by the following PL/SQL statements:
– EXECUTE IMMEDIATE
– OPEN-FOR
– FETCH
– CLOSE


Using the EXECUTE IMMEDIATE Statement

Use the EXECUTE IMMEDIATE statement for Native
Dynamic SQL or PL/SQL anonymous blocks:

EXECUTE IMMEDIATE dynamic_string
[INTO {define_variable
[, define_variable] ... | record}]
[USING [IN|OUT|IN OUT] bind_argument
[, [IN|OUT|IN OUT] bind_argument] ... ];

• INTO is used for single-row queries and specifies
the variables or records into which column values
are retrieved.
• USING is used to hold all bind arguments. The
default parameter mode is IN, if not specified.

Dynamic SQL with a DDL Statement

• Creating a table:
CREATE PROCEDURE create_table(
table_name VARCHAR2, col_specs VARCHAR2) IS
BEGIN
EXECUTE IMMEDIATE 'CREATE TABLE '||table_name||
' (' || col_specs || ')';
END;
/

• Call example:
BEGIN
create_table('EMPLOYEE_NAMES',
'id NUMBER(4) PRIMARY KEY, name VARCHAR2(40)');
END;
/


Dynamic SQL with DML Statements

• Deleting rows from any table:
CREATE FUNCTION del_rows(table_name VARCHAR2)
RETURN NUMBER IS
BEGIN
EXECUTE IMMEDIATE 'DELETE FROM '||table_name;
RETURN SQL%ROWCOUNT;
END;
BEGIN DBMS_OUTPUT.PUT_LINE(
del_rows('EMPLOYEE_NAMES')|| ' rows deleted.');
END;
• Inserting a row into a table with two columns:
CREATE PROCEDURE add_row(table_name VARCHAR2,
id NUMBER, name VARCHAR2) IS
BEGIN
EXECUTE IMMEDIATE 'INSERT INTO '||table_name||
' VALUES (:1, :2)' USING id, name;
END;


Dynamic SQL with a Single-Row Query

Example of a single-row query:
CREATE FUNCTION get_emp(emp_id NUMBER)
RETURN employees%ROWTYPE IS
stmt VARCHAR2(200);
emprec employees%ROWTYPE;
BEGIN
stmt := 'SELECT * FROM employees ' ||
'WHERE employee_id = :id';
EXECUTE IMMEDIATE stmt INTO emprec USING emp_id;
RETURN emprec;
END;
/
DECLARE
emprec employees%ROWTYPE := get_emp(100);
BEGIN
DBMS_OUTPUT.PUT_LINE('Emp: '||emprec.last_name);
END;
/


Dynamic SQL with a Multirow Query

Use OPEN-FOR, FETCH, and CLOSE processing:
CREATE PROCEDURE list_employees(deptid NUMBER) IS
TYPE emp_refcsr IS REF CURSOR;
emp_cv emp_refcsr;
emprec employees%ROWTYPE;
stmt varchar2(200) := 'SELECT * FROM employees';
BEGIN
IF deptid IS NULL THEN OPEN emp_cv FOR stmt;
ELSE
stmt := stmt || ' WHERE department_id = :id';
OPEN emp_cv FOR stmt USING deptid;
END IF;
LOOP
FETCH emp_cv INTO emprec;
EXIT WHEN emp_cv%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(emprec.department_id||
' ' ||emprec.last_name);
END LOOP;
CLOSE emp_cv;
END;


Declaring Cursor Variables

• Declare a cursor type as REF CURSOR:
CREATE PROCEDURE process_data IS
TYPE ref_ctype IS REF CURSOR; -- weak ref cursor
TYPE emp_ref_ctype IS REF CURSOR -- strong
RETURN employees%ROWTYPE;
:

• Declare a cursor variable using the cursor type:
:
dept_csrvar ref_ctype;
emp_csrvar emp_ref_ctype;
BEGIN
OPEN emp_csrvar FOR SELECT * FROM employees;
OPEN dept_csrvar FOR SELECT * from departments;
-- Then use as normal cursors
END;


Dynamically Executing a PL/SQL Block

Executing a PL/SQL anonymous block dynamically:
CREATE FUNCTION annual_sal(emp_id NUMBER)
RETURN NUMBER IS
plsql varchar2(200) :=
'DECLARE '||
' emprec employees%ROWTYPE; '||
'BEGIN '||
' emprec := get_emp(:empid); ' ||
' :res := emprec.salary * 12; ' ||
'END;';
result NUMBER;
BEGIN
EXECUTE IMMEDIATE plsql
USING IN emp_id, OUT result;
RETURN result;
END;
/
EXECUTE DBMS_OUTPUT.PUT_LINE(annual_sal(100))


Using Native Dynamic SQL
to Compile PL/SQL Code

Compile PL/SQL code with the ALTER statement:
• ALTER PROCEDURE name COMPILE
• ALTER FUNCTION name COMPILE
• ALTER PACKAGE name COMPILE SPECIFICATION
• ALTER PACKAGE name COMPILE BODY
CREATE PROCEDURE compile_plsql(name VARCHAR2,
plsql_type VARCHAR2, options VARCHAR2 := NULL) IS
stmt varchar2(200) := 'ALTER '|| plsql_type ||
' '|| name || ' COMPILE';
BEGIN
IF options IS NOT NULL THEN
stmt := stmt || ' ' || options;
END IF;
EXECUTE IMMEDIATE stmt;
END;
/


Using the DBMS_SQL Package

The DBMS_SQL package is used to write dynamic SQL
in stored procedures and to parse DDL statements.
Some of the procedures and functions of the package
include:
• OPEN_CURSOR
• PARSE
• BIND_VARIABLE
• EXECUTE
• FETCH_ROWS
• CLOSE_CURSOR


Using DBMS_SQL with a DML Statement

Example of deleting rows:
CREATE OR REPLACE FUNCTION delete_all_rows
(table_name VARCHAR2) RETURN NUMBER IS
csr_id INTEGER;
rows_del NUMBER;
BEGIN
csr_id := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(csr_id,
'DELETE FROM '||table_name, DBMS_SQL.NATIVE);
rows_del := DBMS_SQL.EXECUTE (csr_id);
DBMS_SQL.CLOSE_CURSOR(csr_id);
RETURN rows_del;
END;
/
BEGIN DBMS_OUTPUT.PUT_LINE('Rows Deleted: ' ||
delete_all_rows('employees'));
END;


Using DBMS_SQL with a Parameterized
DML Statement
CREATE PROCEDURE insert_row (table_name VARCHAR2,
id VARCHAR2, name VARCHAR2, region NUMBER) IS
csr_id INTEGER;
stmt VARCHAR2(200);
rows_added NUMBER;
BEGIN
stmt := 'INSERT INTO '||table_name||
' VALUES (:cid, :cname, :rid)';
csr_id := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(csr_id, stmt, DBMS_SQL.NATIVE);
DBMS_SQL.BIND_VARIABLE(csr_id, ':cid', id);
DBMS_SQL.BIND_VARIABLE(csr_id, ':cname', name);
DBMS_SQL.BIND_VARIABLE(csr_id, ':rid', region);
rows_added := DBMS_SQL.EXECUTE(csr_id);
DBMS_SQL.CLOSE_CURSOR(csr_id);
DBMS_OUTPUT.PUT_LINE(rows_added||' row added');
END;
/


Comparison of Native Dynamic SQL and
the DBMS_SQL Package

Native Dynamic SQL:
• Is easier to use than DBMS_SQL
• Requires less code than DBMS_SQL
• Enhances performance because the PL/SQL
interpreter provides native support for it
• Supports all types supported by static SQL in
PL/SQL, including user-defined types
• Can fetch rows directly into PL/SQL records


DBMS_METADATA Package

The DBMS_METADATA package provides a centralized
facility for the extraction, manipulation, and
resubmission of dictionary metadata.


Metadata API

Processing involves the following steps:
1. Fetch an object’s metadata as XML.
2. Transform the XML in a variety of ways (including
transforming it into SQL DDL).
3. Submit the XML to re-create the object.


Subprograms in DBMS_METADATA
Name Description
OPEN Specifies the type of object to be retrieved, the version of its
metadata, and the object model. The return value is an opaque
context handle for the set of objects.
SET_FILTER Specifies restrictions on the objects to be retrieved such as the
object name or schema
SET_COUNT Specifies the maximum number of objects to be retrieved in a single
FETCH_xxx call
GET_QUERY Returns the text of the queries that will be used by FETCH_xxx

SET_PARSE_ITEM Enables output parsing and specifies an object attribute to be
parsed and returned
ADD_TRANSFORM Specifies a transform that FETCH_xxx applies to the XML
representation of the retrieved objects
SET_TRANSFORM_PARAM, Specifies parameters to the XSLT stylesheet identified by
SET_REMAP_PARAM transform_handle
FETCH_XXX Returns metadata for objects meeting the criteria established by
OPEN, SET_FILTER
CLOSE Invalidates the handle returned by OPEN and cleans up the
associated state


FETCH_xxx Subprograms

Name Description
FETCH_XML This function returns the XML metadata for an object
as an XMLType.
FETCH_DDL This function returns the DDL (either to create or to
drop the object) into a predefined nested table.
FETCH_CLOB This function returns the objects, transformed or not,
as a CLOB.
FETCH_XML_CLOB This procedure returns the XML metadata for the
objects as a CLOB in an IN OUT NOCOPY parameter
to avoid expensive LOB copies.


SET_FILTER Procedure

• Syntax:

PROCEDURE set_filter
( handle IN NUMBER,
name IN VARCHAR2,
value IN VARCHAR2|BOOLEAN|NUMBER,
object_type_path VARCHAR2
);

• Example:
...
DBMS_METADATA.SET_FILTER (handle, 'NAME', 'HR');
...


Filters

There are over 70 filters, which are organized into
object type categories such as:
• Named objects
• Tables
• Objects dependent on tables
• Index
• Dependent objects
• Granted objects
• Table data
• Index statistics
• Constraints
• All object types
• Database export

Examples of Setting Filters

To set up the filter to fetch the HR schema objects
excluding the object types of functions, procedures,
and packages, as well as any views that contain
PAYROLL in the start of the view name:
DBMS_METADATA.SET_FILTER(handle, 'SCHEMA_EXPR',
'IN (''PAYROLL'', ''HR'')');
DBMS_METADATA.SET_FILTER(handle, 'EXCLUDE_PATH_EXPR',
'=''FUNCTION''');
'=''PROCEDURE''');
'=''PACKAGE''');
DBMS_METADATA.SET_FILTER(handle, 'EXCLUDE_NAME_EXPR',
'LIKE ''PAYROLL%''', 'VIEW');


Programmatic Use: Example 1
CREATE PROCEDURE example_one IS
h NUMBER; th1 NUMBER; th2 NUMBER;
doc sys.ku$_ddls; 1
BEGIN
h := DBMS_METADATA.OPEN('SCHEMA_EXPORT'); 2
DBMS_METADATA.SET_FILTER (h,'SCHEMA','HR'); 3
th1 := DBMS_METADATA.ADD_TRANSFORM (h, 4
'MODIFY', NULL, 'TABLE');
DBMS_METADATA.SET_REMAP_PARAM(th1, 5
'REMAP_TABLESPACE', 'SYSTEM', 'TBS1');
th2 :=DBMS_METADATA.ADD_TRANSFORM(h, 'DDL');
DBMS_METADATA.SET_TRANSFORM_PARAM(th2,
'SQLTERMINATOR', TRUE);
DBMS_METADATA.SET_TRANSFORM_PARAM(th2, 6
'REF_CONSTRAINTS', FALSE, 'TABLE');
LOOP
doc := DBMS_METADATA.FETCH_DDL(h); 7
EXIT WHEN doc IS NULL;
END LOOP;
DBMS_METADATA.CLOSE(h); 8
END;


Notes Page


Programmatic Use: Example 2

CREATE FUNCTION get_table_md RETURN CLOB IS
h NUMBER; -- returned by 'OPEN'
th NUMBER; -- returned by 'ADD_TRANSFORM'
doc CLOB;
BEGIN
-- specify the OBJECT TYPE
h := DBMS_METADATA.OPEN('TABLE');
-- use FILTERS to specify the objects desired
DBMS_METADATA.SET_FILTER(h,'SCHEMA','HR');
DBMS_METADATA.SET_FILTER(h,'NAME','EMPLOYEES');
-- request to be TRANSFORMED into creation DDL
th := DBMS_METADATA.ADD_TRANSFORM(h,'DDL');
-- FETCH the object
doc := DBMS_METADATA.FETCH_CLOB(h);
-- release resources
DBMS_METADATA.CLOSE(h);
RETURN doc;
END;
/


Notes Page


Browsing APIs

Name Description
GET_XXX The GET_XML and GET_DDL functions return
metadata for a single named object.
GET_DEPENDENT_XXX This function returns metadata for a dependent
object.
GET_GRANTED_XXX This function returns metadata for a granted
object.

Where xxx is: DDL or XML


Browsing APIs: Examples

1. Get XML representation of HR.EMPLOYEES:
SELECT DBMS_METADATA.GET_XML
('TABLE', 'EMPLOYEES', 'HR')
FROM dual;
2. Fetch the DDL for all object grants on
HR.EMPLOYEES:
SELECT DBMS_METADATA.GET_DEPENDENT_DDL
('OBJECT_GRANT', 'EMPLOYEES', 'HR')
FROM dual;

3. Fetch the DDL for all system grants granted to HR:
SELECT DBMS_METADATA.GET_GRANTED_DDL
('SYSTEM_GRANT', 'HR')
FROM dual;


Browsing APIs: Examples

BEGIN
DBMS_METADATA.SET_TRANSFORM_PARAM(
DBMS_METADATA.SESSION_TRANSFORM, 1
'STORAGE', false);
END;
/
SELECT DBMS_METADATA.GET_DDL('TABLE',u.table_name)
FROM user_all_tables u 2
WHERE u.nested = 'NO'
AND (u.iot_type IS NULL OR u.iot_type = 'IOT');

BEGIN
DBMS_METADATA.SET_TRANSFORM_PARAM( 3
DBMS_METADATA.SESSION_TRANSFORM, 'DEFAULT'):
END;
/


Summary

In this lesson, you should have learned how to:
• Explain the execution flow of SQL statements
• Create SQL statements dynamically and execute
them using either Native Dynamic SQL statements
or the DBMS_SQL package
• Recognize the advantages of using Native
Dynamic SQL compared to the DBMS_SQL package
• Use DBMS_METADATA subprograms to
programmatically obtain metadata from the data
dictionary


Practice 6: Overview

This practice covers the following topics:
• Creating a package that uses Native Dynamic SQL
to create or drop a table and to populate, modify,
and delete rows from a table
• Creating a package that compiles the PL/SQL code
in your schema
• Using DBMS_METADATA to display the statement to
regenerate a PL/SQL subprogram


plsql les06

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