Adv Plsql2

7/27/2019 Adv Plsql2

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LOB DatatypesOracle and PL/SQL support several variations of LOB (large object)

datatypes.

LOBs can store large amountsfrom 8 to 128 terabytes of binary data and

character text data. Eg: Used for storing documents, media files, audio

files, movie files etc.,

There are two types of LOBs

Internal LOBs Data is stored within the database (clob, blob, nclob)

External LOBs Data is stored in OS files.(bfile)


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Understanding LOB Locators

Fundamental to working with LOBs is the concept of a LOB locator.

A LOB locator is a pointer to large object data in a database.

Let's see what happens when you select a BLOB column into a BLOB

PL/SQL variable:

DECLARE

photo BLOB;

BEGIN

SELECT photo_col INTO photo .

..

Is photo_col itself retrieved into photo ? NO ! Only a pointer to the photo

is retrieved


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Database LOB columns store LOB locators , and those locators point to

the real data stored elsewhere in the database.

Likewise, PL/SQL LOB variables hold those same LOB locators, which

point to LOB data within the database.

To work with LOB data, you first retrieve a LOB locator, and you then

use a built-in package named DBMS_LOB to retrieve and/or modify the

actual LOB data.


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Comparing null with empty locatorDECLAREv_clob1 clob;v_clob2 clob:=empty_clob();

beginif v_clob1 is null thendbms_output.put_line('v_clob1=null');

end if;if v_clob2 is null thendbms_output.put_line('v_clob2=null');

elsedbms_output.put_line('v_clob2=not null');dbms_output.put_line('length='||length(v_clob2));

end if;end;

/

v_clob1=nullv_clob2=not nulllength=0


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DBMS_LOB package contains


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CLOB example:

CREATE TABLE employees(

empno NUMBER(4),

ename VARCHAR2(15),resume CLOB);

INSERT INTO EMPLOYEES VALUES(7369,'SMITH','Date of Birth:

12-FEB-1945');

INSERT INTO EMPLOYEES VALUES(7566,'JONES','Date of Birth:

15-DEC-1943');

SELECT EMPNO,ENAME,RESUME FROM EMPLOYEES;

SELECT ENAME,DBMS_LOB.SUBSTR(RESUME,12,15) FROM

EMPLOYEES;


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BLOB Example

Initially create a folder in 'C:\PICTURES' & place some images with

extension ".jpg".

Let files have the names SMITH.JPG,JONES.JPG,KING.JPG etc.,

Create a logical directory "IMAGES" in oracle using DBA account.

CREATE DIRECTORY IMAGES AS 'C:\PICTURES';

GRANT READ ON DIRECTORY IMAGES TO PUBLIC;

CREATE TABLE EMP_PHOTOS(empid NUMBER,photo BLOB);


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Copy the pictures using following procedure into EMP_PHOTOS table

CREATE OR REPLACE PROCEDURE copy_photo(id NUMBER,img VARCHAR2)

IS

v_photo blob;

imgfile bfile;

begin

insert into EMP_PHOTOS values(id,empty_blob())

returning PHOTO into v_photo;

imgfile:=bfilename('IMAGES',img);

dbms_lob.fileopen(imgfile);dbms_lob.loadfromfile(v_photo,imgfile,dbms_lob.getlength(imgfile));

dbms_lob.fileclose(imgfile);

commit;

end;

exec copy_photo(1,'smith.jpg');

exec copy_photo(2,'jones.jpg');

exec copy_phots(3,'king.jpg');


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BFILE Example

CREATE TABLE EMP_PICTURES(ID NUMBER,PICTURE BFILE);

INSERT INTO EMP_PICTURES VALUES(1,BFILENAME('IMAGES',smith.jpg'));

INSERT INTO EMP_PICTURES VALUES(2,BFILENAME('IMAGES','jones.jpg'));

INSERT INTO EMP_PICTURES VALUES(3,BFILENAME('IMAGES','king.jpg'));

To test whether file is existingdeclare

v_file BFILE;

v_file_exists BOOLEAN;

BEGIN

SELECT picture INTO v_file FROM EMP_PICTURES WHERE id=3;v_file_exists := (DBMS_LOB.FILEEXISTS(v_file) = 1);

IF v_file_exists THEN

DBMS_OUTPUT.PUT_LINE('File is existing.');

END IF;

END ;/


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Temporary LOBs

Temporary LOBs provide an interface to support

the creation and deletion of LOBs that act like localvariables

Temporary LOBs can be BLOBs , CLOBs or

NCLOBs

These are not associated with a specific table

Data is stored in your temporary tablespace, not in

tables or memory

Temporary LOBs are faster than persistent LOBsbecause they do not generate any redo or rollback

information


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A temporary LOB can be created using

DBMS_LOB.CREATE TEMPORARY

procedure

The lifetime of a temporary LOB is a session

Temporary LOBs are useful for transforming

data in permanent internal LOBs for example,

changing an image type from GIF to JPEG

A temporary LOB is empty when created and

does not support the EMPTY_B/CLOB()functions


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Creating and freeing temporary LOB

DECLARE

temp_clob CLOB;

temp_blob BLOB;BEGIN

--Assigning a value to a null CLOB or BLOB variable causes

--PL/SQL to implicitly create a session-duration temporary

--LOB for you.

temp_clob :=' http://www.exploringindia.com/south/south.html';

temp_blob := HEXTORAW('7A');

DBMS_LOB.FREETEMPORARY(temp_clob);

DBMS_LOB.FREETEMPORARY(temp_blob);END;

PL/SQL will implicitly free temporary LOBs when they go out of scope

at the end of a block.


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Dynamic SQL

Dynamic SQL refers to SQL statements that are constructed andexecuted at runtime.

Static SQL refers to SQL statements that are fully specified, or fixed,at the time the code containing that statement is compiled. DynamicPL/SQL refers to entire PL/SQL blocks of code that are constructeddynamically, then compiled and executed.

Advantages

By constructing and executing dynamically, you gain a tremendousamount of flexibility. You can also build extremely generic and widelyuseful reusable code.

For an example a reporting application in a data warehouse

environment does not know a table name until runtime. These tablesare named according to the starting month and year of the quarter,for example, inv_01_2003, inv_04_2003, inv_07_2003,inv_10_2003, inv_01_2004, and so on.

You can use dynamic SQL in your reporting application to specify the

table name at runtime.


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What can you do with dynamic SQL

Execute DDL statements - You can only execute queries and DML

statements with static SQL inside PL/SQL. What if you want to create a

table or drop an index?

Support ad-hoc query and update requirements of web-based

applications - A common requirement of Internet applications is that

users may be able to specify which columns they want to see and varythe order in which they see the data

Dynamic SQL can be executed using two methods:

- dbms_sql package

- native dynamic sql (NDS) : NDS is a native part of the PL/SQL

language. It is much easier to use than dbms_sql

NDS EXECUTE IMMEDIATE


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NDS EXECUTE IMMEDIATE statement

Executing DDL commands in procedures. Make sure you have createany table privilege

CREATE OR REPLACE PROCEDURE ddl_proc(p_tabname IN varchar2,p_colnames IN varchar2)

ISv_objname varchar2(30);

BEGINSELECT object_name INTO v_objname FROM USER_OBJECTSWHERE object_name=upper(p_tabname);dbms_output.put_line(p_tabname||' object already exists');

EXCEPTION

WHEN no_data_found THENEXECUTE IMMEDIATE 'CREATE TABLE

'||p_tabname||'('||p_colnames||')';END;/

EXECUTE ddl_proc('mytab','id number(4),name varchar2(12)');

bl


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For Dropping tableCREATE or REPLACE PROCEDURE drop_table (table_name IN VARCHAR2)

ASBEGINEXECUTE IMMEDIATE 'DROP TABLE ' || table_name;

END;/

EXEC DROP_TABLE('t');

D l ti f t bl


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Deleting row from a table

CREATE or REPLACE PROCEDURE delete_row(table_name IN VARCHAR2,condition IN VARCHAR2)

ASwhere_clause VARCHAR2(100) := ' WHERE ' || condition;

BEGINEXECUTE IMMEDIATE 'DELETE ' || table_name || where_clause;

EXCEPTION

WHEN others THENdbms_output.put_line('Exception:'||SQLERRM);

END;/

execute delete_row('emp','empno=7566');

execute delete_row('dept','deptno=40');

U i DBMS SQL


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Using DBMS_SQLOracle lets you to write stored procedures andanonymous PL/SQL blocks that use dynamic SQL.

DBMS_SQL enables you to parse any DML or DDLstatement (syntax/formation of statement).

Therefore, you can parse DDL statements directly using

PL/SQL.

CREATE l PROCEDURE d l t (


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CREATE or replace PROCEDURE delete_row(table_name VARCHAR2,condition varchar2)

IScur_hdl INTEGER;

stmt_str VARCHAR2(200);rows_processed BINARY_INTEGER;

BEGINstmt_str := 'DELETE FROM ' || table_name || ' where ' ||condition;-- open cursor

cur_hdl := dbms_sql.open_cursor;-- parse cursordbms_sql.parse(cur_hdl, stmt_str,dbms_sql.native);-- supply bindsrows_processed := dbms_sql.execute(cur_hdl);

-- close cursordbms_sql.close_cursor(cur_hdl);

END;/

exec delete_row('dept','dname=''SPORTS''');

Th f ll i l d i d SQL hi h i


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The following sample procedure is passed a SQL statement, which it

then parses and runs:

CREATE OR REPLACE PROCEDURE exec(STRING IN varchar2) AS

cursor_name INTEGER;ret INTEGER;

BEGIN

cursor_name := DBMS_SQL.OPEN_CURSOR;

DBMS_SQL.PARSE(cursor_name, string, DBMS_SQL.native);ret := DBMS_SQL.EXECUTE(cursor_name);

DBMS_SQL.CLOSE_CURSOR(cursor_name);

EXCEPTION

WHEN others THEN

dbms_output.put_line('Exception:'||SQLERRM);

END;

/

exec exec('insert into dept values(50,''SPORTS'',''BLORE'')');

E ti Fl


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Execution Flow

OPEN_CURSOR

To process a SQL statement, you must have an open cursor. When you call the

OPEN_CURSOR function, you receive a cursor ID number for the data structurerepresenting a valid cursor maintained by Oracle. These cursors are distinct from

cursors defined at the PL/SQL level, and are used only by the DBMS_SQL package.

PARSE

Every SQL statement must be parsed by calling the PARSE procedure. Parsing the

statement checks the statements syntax and associates it with the cursor in your

program.

EXECUTE

Call the EXECUTE function to run your SQL statement.

CLOSE_CURSOR

When you no longer need a cursor for a session, close the cursor by calling

CLOSE_CURSOR.

BIND VARIABLE BIND ARRAY


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BIND_VARIABLE or BIND_ARRAY

Many DML statements require that data in your program be

input to Oracle. When you define a SQL statement that

contains input data to be supplied at runtime, you must useplaceholders in the SQL statement to mark where data must be

supplied.

For each placeholder in the SQL statement, you must call oneof the bind procedures, BIND_VARIABLE or BIND_ARRAY,

to supply the value of a variable in

your program (or the values of an array) to the placeholder.

When the SQL statement is subsequently run, Oracle uses the

data that your program has placed in the output and input, or

bind variables.

DEFINE COLUMN


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DEFINE_COLUMN

The columns of the row being selected in a SELECT statement are

identified by their relative positions as they appear in the select list, from

left to right. For a query, you must call one of the define procedure

DEFINE_COLUMN to specify the variables that are to receive theSELECT values, much the way an INTO clause does for a static query.

FETCH_ROWS

The FETCH_ROWS function retrieves the rows that satisfy the query.Each successive fetch retrieves another set of rows, until the fetch is

unable to retrieve anymore rows.

VARIABLE_VALUE, COLUMN_VALUE

For queries, call COLUMN_VALUE to determine the value of a column

retrieved by the FETCH_ROWS call.

For anonymous blocks containing calls to PL/SQL procedures or DML

statements with returning clause, call VARIABLE_VALUE to retrieve

the values assigned to the output variables when statements were run.

CREATE or replace PROCEDURE insert into table(


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CREATE or replace PROCEDURE insert_into_table(

table_name VARCHAR2,

v_deptno integer,

v_dname VARCHAR2,

v_loc VARCHAR2)

IScur_hdl INTEGER;

stmt_str VARCHAR2(200);

rows_processed BINARY_INTEGER;

BEGIN

stmt_str := 'INSERT INTO ' || table_name || ' VALUES (:deptno,:dname,:loc)';

-- open cursorcur_hdl := dbms_sql.open_cursor;

-- parse cursor

dbms_sql.parse(cur_hdl, stmt_str,dbms_sql.native);

-- supply binds

dbms_sql.bind_variable(cur_hdl, ':deptno',v_deptno);

dbms_sql.bind_variable(cur_hdl, ':dname', v_dname);dbms_sql.bind_variable(cur_hdl, ':loc', v_loc);

-- execute cursor

rows_processed := dbms_sql.execute(cur_hdl);

-- close cursor

dbms_sql.close_cursor(cur_hdl);

END;

F f t hi d t f t bl


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For fetching data from emp table

DECLARE

stmt_str varchar2(200);

cur_hdl int;

rows_processed int;

name varchar2(10);

salary int;

BEGIN

cur_hdl := dbms_sql.open_cursor; -- open cursorstmt_str := 'SELECT ename, sal FROM emp WHERE

job = :jobname';

dbms_sql.parse(cur_hdl, stmt_str,dbms_sql.native);-- supply binds (bind by name)

dbms_sql.bind_variable(cur_hdl, 'jobname', 'SALESMAN');

-- describe defines

dbms_sql.define_column(cur_hdl, 1, name, 200);

dbms_sql.define_column(cur_hdl, 2, salary);

rows_processed := dbms_sql.execute(cur_hdl); --execute

LOOP


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LOOP-- fetch a row

IF dbms_sql.fetch_rows(cur_hdl) > 0 then-- fetch columns from the row

dbms_sql.column_value(cur_hdl, 1, name);dbms_sql.column_value(cur_hdl, 2, salary);

dbms_output.put_line(name||','||salary);

ELSE

EXIT;

END IF;

END LOOP;

dbms_sql.close_cursor(cur_hdl); -- close cursor

END;

U d ti d t t bl


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Updating dept_new table

DECLARE

deptname_array dbms_sql.varchar2_table;

cur_hdl INT;

stmt_str VARCHAR2(200);

location VARCHAR2(20);

deptnumber NUMBER := 10;

rows_processed NUMBER;BEGIN

stmt_str := 'UPDATE dept_new

SET loc = :newloc

WHERE deptno = :deptnoRETURNING dname INTO :dname';

cur_hdl := dbms_sql.open_cursor;

dbms_sql.parse (cur_hdl, stmt_str, dbms_sql.native);


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-- supply binds

dbms_sql.bind_variable(cur_hdl, ':newloc', location);

dbms_sql.bind_variable(cur_hdl, ':deptno', deptnumber);

dbms_sql.bind_array(cur_hdl, ':dname', deptname_array);-- execute cursor

rows_processed := dbms_sql.execute(cur_hdl);

-- get RETURNING column into OUT bind array

dbms_sql.variable_value(cur_hdl, ':dname', deptname_array);dbms_sql.close_cursor(cur_hdl);

END;

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