Foreign key

A foreign key is a way to enforce referential integrity within your Oracle database. The referenced table is called the parent table while the table with the foreign key is called the child table. The foreign key in the child table will generally reference a primary key in the parent table.

Set NULL on Delete

A foreign key with "set null on delete" means that if a record in the parent table is deleted, then the corresponding records in the child table will have the foreign key fields set to null. The records in the child table will not be deleted.

Create table emp

(empid number not null,

Ename varchar2(50) not null,

Deptno number not null,

Constraint deptno_pk PRIMARY KEY (deptno)

);

Create table dept

(

Deptno number,

Deptname varchar2(50),

Constraint fk_deptno

FOREIGN KEY(deptno)

REFERENCES EMP(DEPTNO)

ON DELETE SET NULL

);

Cascade DELETE

A foreign key with cascade delete means that if a record in the parent table is deleted, then the corresponding records in the child table with automatically be deleted. This is called a cascade delete in Oracle.

Create table emp

(empid number not null,

Ename varchar2(50) not null,

Deptno number not null,

Constraint deptno_pk PRIMARY KEY (deptno)

);

Create table dept

(

Deptno number,

Deptname varchar2(50),

Constraint fk_deptno

FOREIGN KEY(deptno)

REFERENCES EMP(DEPTNO)

ON DELETE CASCADE

);

SAVEPOINTUse the SAVEPOINT statement to identify a point in a transaction to which you can roll back later.UPDATE employeesSET salary = 7000WHERE last_name = 'Banda';

SAVEPOINT a;

UPDATE employeesSET salary = 12000WHERE last_name = 'Greene';

SAVEPOINT b;

ROLLBACK TO SAVEPOINT a;

COMMIT;

What is View :-

View is database object which is usually providing the authority of security levels. View doesn’t store data. View is virtual table. it is created by a query joining one or more tables.

Sytax

Create view ViewName as select columns from tables

Types of views

1) Simple view

What is PL/SQL?

PL/SQL stands for Procedural Language extension of SQL.PL/SQL is a combination of SQL along with the procedural features of programming languages.It was developed by Oracle Corporation in the early 90’s to enhance the capabilities of SQL.

The PL/SQL Engine:Oracle uses a PL/SQL engine to processes the PL/SQL statements. A PL/SQL code can be stored in the client system (client-side) or in the database (server-side).

A Simple PL/SQL Block:

Each PL/SQL program consists of SQL and PL/SQL statements which from a PL/SQL block.

PL/SQL Block consists of three sections:

The Declaration section (optional). The Execution section (mandatory). The Exception (or Error) Handling section (optional).

Declaration Section:

The Declaration section of a PL/SQL Block starts with the reserved keyword DECLARE. This section is optional and is used to declare any placeholders like variables, constants, records and cursors, which are used to manipulate data in the execution section. Placeholders may be any of Variables, Constants and Records, which stores data temporarily. Cursors are also declared in this section.

Execution Section:

The Execution section of a PL/SQL Block starts with the reserved keyword BEGIN and ends with END. This is a mandatory section and is the section where the program logic is written to perform any task. The programmatic constructs like loops, conditional statement and SQL statements form the part of execution section.

Exception Section:

The Exception section of a PL/SQL Block starts with the reserved keyword EXCEPTION. This section is optional. Any errors in the program can be handled in this section, so that the PL/SQL Blocks terminates gracefully. If the PL/SQL Block contains exceptions that cannot be handled, the Block terminates abruptly with errors.

Every statement in the above three sections must end with a semicolon ; . PL/SQL blocks can be nested within other PL/SQL blocks. Comments can be used to document code.

How a Sample PL/SQL Block Looks

DECLARE      Variable declarationBEGIN      Program Execution EXCEPTION      Exception handlingEND;

Advantages of PL/SQL

Block Structures: PL SQL consists of blocks of code, which can be nested within each other. Each block forms a unit of a task or a logical module. PL/SQL Blocks can be stored in the database and reused.

 Procedural Language Capability: PL SQL consists of procedural language constructs such as

conditional statements (if else statements) and loops like (FOR loops).  Better Performance: PL SQL engine processes multiple SQL statements simultaneously as a single

block, thereby reducing network traffic. Error Handling: PL/SQL handles errors or exceptions effectively during the execution of a PL/SQL

program. Once an exception is caught, specific actions can be taken depending upon the type of the exception or it can be displayed to the user with a message.

DECLARE  var_salary number(6);  var_emp_id number(6) = 1116; BEGIN SELECT salary  INTO var_salary

 FROM employee  WHERE emp_id = var_emp_id;  dbms_output.put_line(var_salary);  dbms_output.put_line('The employee ' || var_emp_id || ' has salary ' || var_salary); END; /

Scope of PS/SQL Variables

Local variables - These are declared in a inner block and cannot be referenced by outside Blocks. Global variables - These are declared in a outer block and can be referenced by its itself and by

its inner blocks.

PL/SQL Constants

Constant is a value used in a PL/SQL Block that remains unchanged throughout the program.

constant_name CONSTANT datatype := VALUE;

DECLARE  salary_increase CONSTANT number(3); BEGIN  salary_increase := 100; dbms_output.put_line (salary_increase); END;

Iterative Statements in PL/SQL

Iterative control Statements are used when we want to repeat the execution of one or more statements for specified number of times.

There are three types of loops in PL/SQL:

• Simple Loop• While Loop• For Loop

1) Simple Loop

A Simple Loop is used when a set of statements is to be executed at least once before the loop terminates. An EXIT condition must be specified in the loop, otherwise the loop will get into an infinite number of iterations.LOOP statements; EXIT; {or EXIT WHEN condition;}END LOOP;

2) While Loop

A while loop repeats set of statements in the plsql block as long as a condition is true. The iteration continues until the condition becomes false.

WHILE <condition> LOOP statements; END LOOP;

3) For Loop

A for loop is used to execute a set of statements in plsql block for predetermined number of times. Iteration occurs between the start and end integer values given. The counter is always incremented by 1. The loop exits when the counter reachs the value of the end integer.

FOR counter IN val1..val2 LOOP statements; END LOOP;

Cursors

A cursor is a temporary work area created in the system memory when a SQL statement is executed. This temporary work area is used to store the data retrieved from the database, and manipulate this data. A cursor can hold more than one row, but can process only one row at a time. The set of rows the cursor holds is called the active set.

Syntax

DeclareCURSOR [cursor name] [parameter]Retrun [return type]IsSelect statementBeginOpen [cursor name];Fetch [cursor name] into [return value];Close [cursor name];End;

Eg :--

Declare cursor c1 is select * from emp;V_emp emp%rowtype;BeginOpen c1;LoopFetch c1 into v_emp;Dbms_output.put_line(‘The emp name is ‘||v_emp.ename);

End loop;Close c1;End;

TYPES OF CURSORS

There are two types of cursors

(1) An IMPLICIT cursor is automatically declared by Oracle every time an SQL statement is executed. The user will not be aware of this happening and will not be able to control or process the information in an implicit cursor.

DECLARE var_rows number (5);BEGIN UPDATE employee SET salary = salary + 1000; IF SQL%NOTFOUND THEN dbms_output.put_line('None of the salaries where updated'); ELSIF SQL%FOUND THEN var_rows := SQL%ROWCOUNT; dbms_output.put_line('Salaries for ' || var_rows || 'employees are updated'); END IF; END;

(2) An EXPLICIT cursor is defined by the program for any query that returns more than one row of

data. That means the programmer has declared the cursor within the PL/SQL code block. This declaration allows for the application to sequentially process each row of data as it is returned by the cursor.

DECLARE CURSOR emp_cur IS SELECT first_name, last_name, salary FROM emp_tbl; emp_rec emp_cur%rowtype; BEGIN IF NOT sales_cur%ISOPEN THEN OPEN sales_cur; END IF; LOOP FETCH emp_cur INTO emp_rec; EXIT WHEN emp_cur%NOTFOUND; dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name || ' ' ||emp_cur.salary); END LOOP; END; /

Explicit Cursor Attributes

%NOTFOUND cursor_name%NOTFOUND A Boolean attribute that re-turns TRUE if the previous FETCH did not return a row, and FALSE if it did.

%FOUND cursor_name%FOUND A Boolean attribute that re-turns TRUE if the previous FETCH returned a row, and FALSE if it did not.

%ROWCOUNT cursor_name%ROWCOUNT # of records fetched from a cursor at that point in time.

%ISOPEN cursor_name%ISOPEN A Boolean attribute that re-turns TRUE if cursor is open, FALSE if it is not.

Cursor with a FOR Loop:

When using FOR LOOP you need not declare a record or variables to store the cursor values, need not open, fetch and close the cursor. These functions are accomplished by the FOR LOOP automatically.

DECLARE CURSOR emp_cur IS SELECT first_name, last_name, salary FROM emp_tbl; emp_rec emp_cur%rowtype; BEGIN FOR emp_rec in sales_cur LOOP dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name || ' ' ||emp_cur.salary); END LOOP; END;/

Ref Cursor

A ref cursor is a data type that holds a cursor value in the same way that a varchar2 variable will hold a string value. A ref cursor can be opened on the server and passed to the client as a unit rather than fetching one row at a time. One can use a ref cursor as target of an assignment, and it is can be passed as parameter to other program units. Ref cursors are opened with an OPEN FOR statement. In most other ways they behave like normal cursors.

Eg :

declaretype x is ref cursor;y x;stmt varchar2(200) := 'select * from emp where deptno= :X1';V_deptno varchar2(10) := 10;emp_rec emp%rowtype;beginopen y for stmt using v_deptno;loopfetch y into emp_rec;exit when y%notfound

dbms_output.put_line(emp_rec.ename||' , '|| emp_rec.deptno);end loop;close y;end;

Passing parameter and Cursor within cursor

DeclareCursor curdept is select distinct deptno from dept;Cursor curemp(vardeptno dept.deptno%type) is select * from emp where deptno=vardeptno;BeginFor x in curdeptLoopFor y in curemp(x.deptno) LoopInsert into empdept(empno,ename,doj,sal,deptno,deptname,username,pwd) values(y.empno,y.ename,y.doj,y.sal,x.deptno,x.deptname,x.username,x.pwd);End loop;End loop;End;

Inline Cursor

A inline cursor is a cursor that is not declared in the declare section but the cursor definition is included in FOR loop.

DeclareVusername emp.username%type;Vpwd emp.pwd%type;BeginFor I in(select empno,f_name,l_name,sal from emp)LoopVusername :=substr(i.f_name,2,3);V_pwd:=substr(i.l_name,-2,2);Update emp set username =vusername,pwd=vpwd ;End loop;Commit;End;

For update of clause

Used to block the fetched rows from accessing it by other users.

DeclareVsal number;Cursor curempsal is select sal from emp where deptno=10) for update of sal;BeginOpen curempsal;

LoopFetch curempsal into vsal;Exit when curempsal %notfound;Update emp set sal=sal+vsal*1.10 where current of curempsal;End loop;Close curempsal;End;

Examples

--ANOTHER EG DISPLAYING VALUE OF A TABLE

DECLARECURSOR c1 IS SELECT * FROM emp;e_rec emp%rowtype;BEGINOPEN c1;LOOPFETCH c1 INTO e_rec;DBMS_OUTPUT.PUT_LINE('Number: ' || ' ' || e_rec.empno);DBMS_OUTPUT.PUT_LINE('Name : ' || ' ' || e_rec.ename);DBMS_OUTPUT.PUT_LINE('Salary: ' || ' ' || e_rec.sal);EXIT WHEN c1%NOTFOUND;END LOOP;CLOSE c1;END;

-- Display details of Highest 10 salary paid employee

DECLARECURSOR c1 IS SELECT * FROM emp ORDER BY sal DESC;e_rec emp%rowtype;BEGINFOR e_rec IN c1LOOPDBMS_OUTPUT.PUT_LINE('Number: ' || ' ' || e_rec.empno);DBMS_OUTPUT.PUT_LINE('Name : ' || ' ' || e_rec.ename);DBMS_OUTPUT.PUT_LINE('Salary: ' || ' ' || e_rec.sal);EXIT WHEN c1%ROWCOUNT >= 10;END LOOP;END;

-- EXAMPLE OF CURSOR FOR LOOP

declare cursor c1 is select * from somdutt;beginfor outvariable in c1loop

exit when c1%notfound;if outvariable.age < 21 thendbms_output.put_line(outvariable.age || ' ' || outvariable.name);end if;end loop;end;

--ref STRONG CURSORS

DECLARETYPE ecursor IS REF CURSOR RETURN emp%ROWTYPE;ecur ecursor;e_rec emp%ROWTYPE;dn NUMBER;BEGINdn := &deptno;OPEN ecur FOR SELECT * FROM emp WHERE deptno = dn;FOR e_rec IN ecurLOOPDBMS_OUTPUT.PUT_LINE ('Employee No : ' || e_rec.empno);DBMS_OUTPUT.PUT_LINE ('Employee Salary: ' || e_rec.salary);END LOOP;END;

--REF WEAK CURSORS

DECLARETYPE tcursor IS REF CURSOR;tcur tcursor;e1 emp%ROWTYPE;d1 dept%ROWTYPE;tname VARCHAR2(20);BEGINtname := &tablename;IF tname = 'emp' THENOPEN tcur FOR SELECT * FORM emp;DBMS_OUTPUT.PUT_LINE ('Emp table opened.');close tcur;DBMS_OUTPUT.PUT_LINE ('Emp table closed.');ELSE IF tname = 'dept' THENOPEN tcur FOR SELECT * FROM dept;DBMS_OUTPUT.PUT_LINE ('Dept table opened.');close tcur;DBMS_OUTPUT.PUT_LINE ('Emp table closed.');ELSERAISE_APPLICATION_ERROR (-20004, 'Table name is wrong');END IF;END;

--CURSOR FOR LOOP WITH PARAMETERS

DeclareCursor c1(Dno number) is select * from emp where deptno = dno;beginfor empree in c1(10) loop;dbms_output.put_line(empree.ename);end loop;end;

Procudere

Procedure is a named block which are logically grouped sql and plsql statements that performs specific tasks.

Syntax:-

CREATE [OR REPLACE] PROCEDURE proc_name [<IN,OUT,INOUT> <DATATYPE>] IS Declaration section BEGIN Execution section EXCEPTION Exception section END;

IN

An IN parameter whose values is passed into a procedure. The value of IN parameter is constant.

OUT

An out parameter whose values is passed out of the stored procedure.

INOUT

An INOUT Parameter whose values is passed into stored procedure and new value can be assigned to the parameter and passed out of the procedure. INOUT is not constant.

Eg:-

Create or replace procedure Acc_credit(v_accno number,v_creditamnt number)AsV_bal number;V_updbal number;BeginSelect curbal into v_bal from accounts where accno=v_accno for update of curbal;V_updbal:=v_bal+v_creditamnt;

Update accounts set curbal=v_updbal where accno=v_accno;Commit;ExceptionWhen no_Data_Found thenInsert into accounts (accno,curbal) values(v_accno,v_creditamnt);When others thenRollback;End acc_credit;/Execution of procedure

Exec acc_credit(2,2000);Exec acc_credit(15,15000);

Advantages of Procedure are

1) Extensionality 2) Modularity3) Maintainability4) Reusability5) One time compilation

PL/SQL Functions

A function is a named PL/SQL Block which is similar to a procedure. The major difference between a procedure and a function is, a function must always return a value, but a procedure may or may not return a value.

CREATE [OR REPLACE] FUNCTION function_name [parameters] RETURN return_datatype; IS Declaration_section BEGIN Execution_section Return return_variable; EXCEPTION exception section Return return_variable; END;

CREATE OR REPLACE FUNCTION employer_details_func RETURN VARCHAR(20);IS emp_name VARCHAR(20); BEGIN

SELECT first_name INTO emp_name

FROM emp_tbl WHERE empID = '100';RETURN emp_name;

END;/

Difference between Procedure and Function

Procedure FunctionA procedure may return one or more values through parameters or may not return values at all.

A function always returns a value using return statement.

A procedure doesn’t contain return clause in header and exec part

A function contains return clause in header and exec part.

Select statement query can call function. Select sql query can’t call procedure.DML statements can be used in procedure DML can’t be used in function.Procedures are used for business logic purposes Functions are used for computations or calculation

purposes.

Packages:

Oracle allows grouping stored procedures, functions, variables, constants, cursors and exceptions into packages.

A package consist of

1) Package specification: - -

The package specification contains information about the package. The package specification lists the available procedures and functions. The package specification generally doesn't contain the code.

2) Package body: -- The package body contains the actual code.

Advantages

1) We can reduce input/output operations2) Multiple interactions with database.3) Improve performance while accessing sub programs from remote client.4) Over loading

Syntax for package specification

Create or replace package <package name>

{is/as}

<package specification>

End <package name>;

Syntax for package Body

create or replace package body <package name>

{is/as}

<package body>

End <package name>;

INVOKING PACKAGE

Exec <package name>.<sub program>(<list of parameters>);

Recompile Package

Alter package <package name> compile package

Drop Package

Drop package <package name>

PACKAGE OVER LOADING

The same procedure name is repeated with parameters with different datatypes.

PL/SQL Records

Records are composite datatypes, which means it is a combination of different scalar datatypes like char, varchar, number etc.  TYPE rec record is to be used whenever query returns columns of different tables views and variables.

TYPE record_type_name IS RECORD(first_col_name column_datatype,second_col_name column_datatype, ...);

Dynamically define the datatype of a column based on a database column as given below

col_name table_name.column_name%type;

Eg:-

Declare

Type ABC is record (a number,b date);

x abc;beginx.a:=5;x.b:=’11-jul-2014’;end;

PL/SQL Collections

Collections are composite data types. Collections allow treating several variables as a unit. A collection combines variables of the same type.

The types of collections are

1) VARRAYS2) NESTED TABLES3) INDEX BY TABLES (ASSOCIATE ARRAYS)

VARRAY: -- A VARRAY is data type similar to an array. A VARRAY has a fixed limit on its size, Specified as part of declaration. Elements are inserted into VARRAY starting at index 1, up to maximum length declared in the varray type. The maximum size of the VARRAY is 2 GB.

Syntax: -- TYPE <type name> is VARRAY (<Limit>) of <element type>;

Eg:--

Declare Type ABC is varray(10) of number;V1 ABC :=abc(1,2,3,4,5,6)BeginDbms_output.put_line(v1(1));End;

By using select query

DeclareType abc is varray (10) of number;V2 abc;Cusrsor c1 is select empno from emp where rownum<10;V_emp abc;Counter number :=1;BeginV2:=abc();For I in 1 .. 10LoopV2.extend();

V2(i):=i;Dbms_output.put_line(v2(i));End loop;V_emp :=abc();For rec in c1 LoopV_emp.extend();V_emp(Counter) :=rec.empno;Counter:=counter+1;Dbms_output.put_line(v_emp(Counter));End loop;End;

Different Types of METHODS for varray and nested table :--

1) COUNT :-- Returns the total number of elements that a collection currently contains.2) LIMIT :-- Returns the Maximum number of elements for a Varray or NULL for Nested Tables.3) EXISTS(N) :-- Returns TRUE if the Nth element in a collection exists; otherwise FALSE.4) FIRST :-- Returns the First index numbers in a collection that uses integer subscripts.

LAST :-- Returns the Last index numbers in a collection that uses integer subscripts.5) PRIOR :-- Returns the index number that precedes index N in a collection6) NEXT :-- Returns the index number that succeeds index N.7) EXTEND :-- Add a null element to a collection.8) TRIM :-- Removes one element from the end of a collection

Eg :--

TYPE ABC IS Varray(10) of number;V abc:=abc(1,2,3,4,5,6);

1 2 3 4 5 6BeginDbms_output.put_line(‘v1.count ‘ ||v1.count); 6Dbms_output.put_line(‘v1.limit’ || v1.limit); 10Dbms_output.put_line(‘v1.first’|| v1.first); 1Dbms_output.put_line(‘v1.last’ || v1.last); 6V1.trim(2) 5 and 6 index are deleted

1 2 3 4For I in v1.first .. v1.lastloopDbms_output.put_line(v1); 1,2,3,4End loopDbms_output.put_line(‘v1.last ‘|| v1.last); 4End;/

NESTED TABLES

A Nested table is thought of a database table which has no limit on its size. Elements are inserted into nested table starting at index 1. The maximum size of the varray is 2 GB.

SYNTAX :--

Type <type name> is table of <table type>;

Eg:--

Declare Type abc is table of number;V2 abc;Cursor c1 is select empno from emp;V_emp abc;Counter number :=1;BeginV_emp :=abc();For rec in c1 LoopV_emp.extend();V_emp(counter):=rec.empno;Counter:=counter+1;Dbms_output.put_line(V_emp(counter))End loop;end;

INDEX-BY TABLE (ASSOCIATE ARRAY) :--An Index-by table has no limit on its size. Elements are inserted into index-by table whose index may start non sequentially including negative integers.Syntax :--Type <type name> is table of <table type> index by binary integer;Eg:DeclareType ABC is table of date index by pls_integer;V abc;BeginFor I in 1..10LoopV(i):=sysdate+I;End loop;If (v.exists(11)) then Dbms_output.put_line(‘elements exists’);ElseDbms_output.put_line(‘elements not exists’);End if;Dbms_output.put_line(‘total no of elements’||v.count); 10v.delete(7);Dbms_output.put_line(‘total no of elements’||v.count); 9

v.delete(8,10); 8,9,10 deleted.Dbms_output.put_line(‘total no of elements’||v.count); 6For I in v.first..v.lastDbms_output.put_line(‘the elements are’||v(i)); 6 dates will printEnd loop;Dbms_output.put_line(‘next element is’||v.next(4)); 5Dbms_output.put_line(‘next element is’||v.prior(4)); 3End;/

Different Types of METHODS index by table:--

1) COUNT :-- Returns the total number of elements that a collection currently contains.2) LIMIT :-- Returns the Maximum number of elements for a Varray or NULL for Nested Tables.3) EXISTS(N) :-- Returns TRUE if the Nth element in a collection exists; otherwise FALSE.4) FIRST :-- Returns the First index numbers in a collection that uses integer subscripts.

LAST :-- Returns the Last index numbers in a collection that uses integer subscripts.5) PRIOR :-- Returns the index number that precedes index N in a collection6) NEXT :-- Returns the index number that succeeds index N.7) EXTEND :-- Add a null element to a collection.8) DELETE(N) :-- DELETE N element from the collection

BULK COLLECT:--Bulk Collect is used to retrieve all the records from the cursor into the array in one short. It will increase the performance and it will reduce the context switches between sql engine and plsql engine.

The examples of bulk collect

DeclareType t_eno is table of emp.empno%type;Type t_ename is table of emp.ename%type;V_eno t_eno;V_ename t_ename;Cursor c1 is select empno,ename from emp;BeginOpen c1;Fetch c1 bulk collect into v_eno,v_ename;Close c1;For I in v_eno.first .. v_eno.lastLoopDbms_output.put_line(‘empno is ‘||v_eno(i) || ‘emp name is ‘ ||v_ename(i));End loop;End;

2nd example

Declare Type abc is table of emp%rowtype index by pls_integer;V abc;X number;Y emp%rowtype;BeginSelect * from bulk collect into v from emp;X:=1;LoopDbms_output.put_line(v(x).ename);X:=v.next(x);Exit when x is null;End loop;End;/

For ALL or Bulk bind

Bulk binds with Insert, Update and Delete statements, you enclose the SQL statement within a PL/SQL FORALL statement. To do bulk binds with Select  statements, you include the Bulk Collect INTO a collection clause in the SELECT Statement instead of using Simply into

Create table test (a varchar2(1000));

DeclareType t_test is table of test.a%type index by pls_integer;V_Rec t_Test;Begin For all I in v_rec.first..v_rec.lastInsert into test values(v_rec(i));Commit;End;

2nd example

CREATE OR REPLACE PROCEDURE fast_proc (p_array_size IN PLS_INTEGER DEFAULT 100)IS

TYPE ARRAY IS TABLE OF all_objects%ROWTYPE;l_data ARRAY;

CURSOR c ISSELECT *FROM all_objects;

BEGIN    OPEN c;    LOOP    FETCH c BULK COLLECT INTO l_data LIMIT p_array_size;

    FORALL i IN 1..l_data.COUNT    INSERT INTO t2 VALUES l_data(i);

    EXIT WHEN c%NOTFOUND;    END LOOP;    CLOSE c;END fast_proc;/

3rd example

create or replace procedure fast_proc is         type TObjectTable is table of ALL_OBJECTS%ROWTYPE;         ObjectTable$ TObjectTable;         begin         select                     * BULK COLLECT INTO ObjectTable$         from ALL_OBJECTS;

         forall x in ObjectTable$.First..ObjectTable$.Last       insert into t1 values ObjectTable$(x) ;       end; /

EXCEPTIONS HANDLING

PL/SQL provides a feature to handle the Exceptions which occur in a PL/SQL Block known as exception Handling. Using Exception Handling we can test the code and avoid it from exiting abruptly.

PL/SQL Exception message consists of three parts. 1) Type of Exception2) An Error Code3) a messagekSyntax:--

DECLARE Declaration section

BEGIN Exception section EXCEPTION WHEN ex_name1 THEN -Error handling statements WHEN ex_name2 THEN -Error handling statements WHEN Others THEN -Error handling statements END;

Types of Exception.

There are 3 types of Exceptions.

Implicit exception a) Named System Exceptions or predefined exceptionb) Unnamed System Exceptions or non-predefined exception

Explicit Exceptionc) User-defined Exceptions

Named System Exceptions

System exceptions are automatically raised by Oracle, when a program violates a RDBMS rule. There are some system exceptions which are raised frequently, so they are pre-defined and given a name in Oracle which are known as Named System Exceptions.

BEGIN Execution sectionEXCEPTION WHEN NO_DATA_FOUND THEN dbms_output.put_line ('A SELECT...INTO did not return any row.'); END; Pre-defined exceptions are

Exception Raised when ...

CURSOR_ALREADY_OPEN Your program attempts to open an already open cursor. A cursor must be closed before it can be reopened. A cursor FOR loop automatically opens the cursor to which it refers. So, your program cannot open that cursor inside the loop.

DUP_VAL_ON_INDEX Your program attempts to store duplicate values in a database column that is constrained by a unique index.

INVALID_CURSOR Your program attempts an illegal cursor operation such as closing an unopened cursor.

INVALID_NUMBER In a SQL statement, the conversion of a character string into a

Exception Raised when ...

number fails because the string does not represent a valid number. (In procedural statements, VALUE_ERROR is raised.) This exception is also raised when the LIMIT-clause expression in a bulk FETCH statement does not evaluate to a positive number.

LOGIN_DENIED Your program attempts to log on to Oracle with an invalid username and/or password.

NO_DATA_FOUND A SELECT INTO statement returns no rows, or your program references a deleted element in a nested table or an uninitialized element in an index-by table. SQL aggregate functions such as AVG and SUM always return a value or a null. So, a SELECT INTO statement that calls an aggregate function never raises NO_DATA_FOUND. The FETCH statement is expected to return no rows eventually, so when that happens, no exception is raised.

NOT_LOGGED_ON Your program issues a database call without being connected to Oracle.

PROGRAM_ERROR PL/SQL has an internal problem.

ROWTYPE_MISMATCH The host cursor variable and PL/SQL cursor variable involved in an assignment have incompatible return types. For example, when an open host cursor variable is passed to a stored subprogram, the return types of the actual and formal parameters must be compatible.

STORAGE_ERROR PL/SQL runs out of memory or memory has been corrupted.

SUBSCRIPT_BEYOND_COUNT

Your program references a nested table or varray element using an index number larger than the number of elements in the collection.

SUBSCRIPT_OUTSIDE_LIMIT Your program references a nested table or varray element using an index number (-1 for example) that is outside the legal range.

TIMEOUT_ON_RESOURCE A time-out occurs while Oracle is waiting for a resource.

TOO_MANY_ROWS A SELECT INTO statement returns more than one row.

VALUE_ERROR An arithmetic, conversion, truncation, or size-constraint error occurs. For example, when your program selects a column value into a character variable, if the value is longer than the declared length of the variable, PL/SQL aborts the assignment and raises VALUE_ERROR. In procedural statements, VALUE_ERROR is raised if the conversion of a character string into a number fails. (In SQL statements, INVALID_NUMBER is raised.)

ZERO_DIVIDE Your program attempts to divide a number by zero.

Unnamed System Exceptions

Those system exception for which oracle does not provide a name is known as unamed system exception. These exception do not occur frequently. These Exceptions have a code and an associated message.

There are two ways to handle unnamed sysyem exceptions: By using the WHEN OTHERS exception handler and by bind exception with an oracle error using pragma exception init.

Pragma Exception_init:-- This directive binds a predefined Oracle error number to a programmer defined exception name.

Syntax

DECLARE exception_name EXCEPTION; PRAGMA EXCEPTION_INIT (exception_name, Err_code); BEGIN Execution sectionEXCEPTION WHEN exception_name THEN handle the exceptionEND;

Example

DeclareMy_except EXCEPTION;PRAGMA Exception_init(my_except,-1400);BeginInsert into test values(‘1’,’india’);Insert into test values(‘2’,’usa’);Insert into test values(‘3’,null);ExceptionWhen zero_Divide thenDbms_output.put_line(‘exception occurred and terminated’);When my_except thenDbms_output.put_line(‘cannot insert null values’);End;/

Error Trapping Functions

1) SQLCODE :-- returns the latest code of the error that has occurred2) SQLERRM:-- returns the relevant error msg of the sql codeBy trapping error we can return it to a pragma exception init.

DeclareErr_code number;Err_msg varchar2(100);Num1 number;Num2 number(2)BeginNum2:=20000;

ExceptionWhile other thenErr_code:=SQLCODE;Err_msg:=SQLERRM;Dbms_output.put_line(err_Code ||’ ---- ‘|| err_msg);End;/

User-defined Exceptions

User defined exceptions are explicitly define exceptions based on business rules.

RAISE_APPLICATION_ERROR

Raise Application error is a procedure of package DBMS_STANDARD which allows to issue an user defined error message from stored sub program or database trigger.

Eg:--

DeclareV_empno emp.empno%type :=&empno;V_sal number;E_high_sal exception;BeginSelect sal into v_sal from emp where empno=v_empno;If v_sal>2000 thenRaise e_high_Sal;End if;Update emp set sal=sal*0.01 where empno=v_empno;ExceptionWhen e_high_sal thenRaise_application_error(-20001,’Salary is to high’);End;/

You could use the SQLERRM function to raise an error as follows:

ExceptionWhen other thenRaise_application_error(-20001,’an error was encountered – ‘||SQLCODE||’-ERROR-‘||SQLERRM);END;/

Or you could log the error to a table using the SQLERRM function as follows:

ExceptionWhen others thenErr_code :=sqlcode;

Err_msg := SUBSTR(SQLERRM, 1, 200);Insert into audit_table (error_number,error_message) values(err_code,err_msg);End;/

Triggers

A trigger is a pl/sql block structure which is fired when a DML statements like Insert, Delete, Update is executed on a database table. A trigger is triggered automatically when an associated DML statement is executed.

Syntax for Creating a Trigger

CREATE [OR REPLACE ] TRIGGER trigger_name {BEFORE | AFTER | INSTEAD OF } {INSERT [OR] | UPDATE [OR] | DELETE} [OF col_name] ON table_name [REFERENCING OLD AS o NEW AS n] [FOR EACH ROW] WHEN (condition) BEGIN --- sql statements END;

Types of PL/SQL Triggers

There are two types of triggers based on the which level it is triggered.1) Row level trigger - An event is triggered for each row upated, inserted or deleted. 2) Statement level trigger - An event is triggered for each sql statement executed.

Advantages of Triggers

1) Audit data modifications.2) Log events transparency3) Ensure complex business rules derived columns values automatically4) Implements complex security authorization5) Maintains replicate tables

PL/SQL Trigger Execution Hierarchy

The following hierarchy is followed when a trigger is fired.1) BEFORE statement trigger fires first.2) Next BEFORE row level trigger fires, once for each row affected. 3) Then AFTER row level trigger fires once for each affected row. This events will alternates between BEFORE and AFTER row level triggers.4) Finally the AFTER statement level trigger fires.

Examples

CREATE TABLE product(Message varchar2(50), Current_Date number(32));

1) BEFORE UPDATE, Statement Level: This trigger will insert a record into the table 'product_check' before a sql update statement is executed, at the statement level.

CREATE or REPLACE TRIGGER Before_Update_Stat_product BEFORE UPDATE ON product Begin INSERT INTO product_check Values('Before update, statement level',sysdate); END; /

BEFORE UPDATE, Row Level: This trigger will insert a record into the table 'product_check' before each row is updated.

CREATE or REPLACE TRIGGER Before_Upddate_Row_product BEFORE UPDATE ON product FOR EACH ROW BEGIN INSERT INTO product_check Values('Before update row level',sysdate); END; /

3) AFTER UPDATE, Statement Level: This trigger will insert a record into the table 'product_check' after a sql update statement is executed, at the statement level.

CREATE or REPLACE TRIGGER After_Update_Stat_product AFTER UPDATE ON product

BEGIN INSERT INTO product_check Values('After update, statement level', sysdate); End; /

4) AFTER UPDATE, Row Level: This trigger will insert a record into the table 'product_check' after each row is updated.

CREATE or REPLACE TRIGGER After_Update_Row_product AFTER insert On product FOR EACH ROW BEGIN INSERT INTO product_check Values('After update, Row level',sysdate); END; / DESC USER_TRIGGERS;

UNIX

cd -- change directory--------------------------------------------cd (also chdir in some shells) change directorycd changes to user's home directorycd / changes directory to the system's rootcd .. goes up one directory levelcd ../.. goes up two directory levelscd ~username/directory changes directory to the named username's indicated directory

mkdir - make a directoryrmdir - remove directoryls - list directory contents The command to list your directories and files is ls. With options it can provide information about the size, type of file, permissions, dates of file creation, change and access

Syntaxls [options] [argument]

file access permissions: the first 3 characters refer to the permissions for the user, the next three for the users in the Unixgroup assigned to the file, and the last 3 to the permissions for other users on the system.

r read permissionw write permissionx execute permission- no permission

ExamplesTo list the files in a directory:% lsdemofiles frank lindaTo list all files in a directory, including the hidden (dot) files try:% ls -a. .cshrc .history .plan .rhosts frank.. .emacs .login .profile demofiles lindaTo get a long listing:% ls -altotal 24drwxr-sr-x 5 workshop acs 512 Jun 7 11:12 .drwxr-xr-x 6 root sys 512 May 29 09:59 ..-rwxr-xr-x 1 workshop acs 532 May 20 15:31 .cshrc-rw------- 1 workshop acs 525 May 20 21:29 .emacs-rw------- 1 workshop acs 622 May 24 12:13 .history-rwxr-xr-x 1 workshop acs 238 May 14 09:44 .login-rw-r--r-- 1 workshop acs 273 May 22 23:53 .plan-rwxr-xr-x 1 workshop acs 413 May 14 09:36 .profile-rw------- 1 workshop acs 49 May 20 20:23 .rhostsdrwx------ 3 workshop acs 512 May 24 11:18 demofilesdrwx------ 2 workshop acs 512 May 21 10:48 frankdrwx------ 3 workshop acs 512 May 24 10:59 linda

cp - copy a file

cp old_filename new_filename

mv - move a fileRename a file with the move command, mv.mv old_filename new_filenamerm - remove a fileRemove a file with the rm, remove, command.chmod - change file permissionsread=4, write=2, execute=1 or read=r, write=w, execute=x+ add permissions- remove permissions= set permissionschown - change ownershipchown new_owner filechgrp - change groupchgrp new_group fileecho - echo a statement (print the value)echo Hello Class or echo "Hello Class"cat - concatenate a fileDisplay the contents of a file with the concatenate command, cat.head - display the start of a filehead displays the head, or start, of the filetail - display the end of a file

df - summarize disk block and file usage du - report disk space in useps is used to report on processes currently running on the system.kill - terminate a processwho - list current userswho reports who is logged in at the present time.Syntaxwho [am i]whereis - report program locationswhereis reports the filenames of source, binary, and manual page files associated with command(s).hostname/uname - name of machinescript - record your screen I/Odate - current date and timeSyntaxdate [options] [+format]Common Options-u use Universal Time (or Greenwich Mean Time)+format specify the output format%a weekday abbreviation, Sun to Sat%h month abbreviation, Jan to Dec%j day of year, 001 to 366%n <new-line>%t <TAB>%y last 2 digits of year, 00 to 99%D MM/DD/YY date%H hour, 00 to 23%M minute, 00 to 59%S second, 00 to 59%T HH:MM:SS timeExamplesbeauty condron>dateMon Jun 10 09:01:05 EDT 1996beauty condron>date -uMon Jun 10 13:01:33 GMT 1996beauty condron>date +%a%t%DMon 06/10/96beauty condron>date '+%y:%j'96:162

lp/lpr - submit a print job

lp [options] filenamelpr [options] filename

example : -- lp ssh.ps

lpstat/lpq - check the status of a print job

cancel/lprm - cancel a print job

pr - prepare files for printing

Common Options+page_number start printing with page page_number of the formatted input file-column number of columns-a modify -column option to fill columns in round-robin order-d double spacing-e[char][gap] tab spacing-h header_string header for each page-l lines lines per page-t don’t print the header and trailer on each page-w width width of pageExamplesThe file containing the list of P. G. Wodehouse’s Lord Emsworth books could be printed, at 14 linesper page (including 5 header and 5 (empty) trailer lines) below, where the -e option specifies the<tab> conversion style:% pr -l 14 -e42 wodehouseApr 29 11:11 1996 wodehouse_emsworth_books Page 1Something Fresh [1915] Uncle Dynamite [1948]Leave it to Psmith [1923] Pigs Have Wings [1952]Summer Lightning [1929] Cocktail Time [1958]Heavy Weather [1933] Service with a Smile [1961]

Apr 29 11:11 1996 wodehouse_emsworth_books Page 2Blandings Castle and Elsewhere [1935] Galahad at Blandings [1965]Uncle Fred in the Springtime [1939] A Pelican at Blandings [1969]Full Moon [1947] Sunset at Blandings [1977]

DUAL

This is a single row and single column dummy table provided by oracle. This is used to perform mathematical calculations without using a table.

Group By

The Oracle GROUP BY Clause is used in a select statement to collect data across multiple records and group the results by one or more columns.

Having By

The Oracle HAVING Clause is used in combination with the group by clause to restrict the groups of returned rows to only those whose the condition is TRUE.

Where Clause

The Oracle WHERE clause is used to filter the results from a select,insert,update and delete statement.

From Clause

The Oracle/PLSQL FROM clause is used to list the tables and any join information required for the Oracle query.

Distinct Clause

The Oracle DISTINCT clause is used to remove duplicates from the result set. The DISTINCT clause can only be used with select statements.

Order By

The Oracle ORDER BY clause is used to sort the records in your result set. The ORDER BY clause can only be used in select statements.

Mutating Error

Mutating error normally occurs when we are performing some DML operations and we are trying to select the affected record from the same trigger. So basically we are trying to select records in the trigger from the table that owns the trigger. This creates inconsistency and Oracle throws a mutating error.

How can one see if somebody modified any code?Code for stored procedures, functions and packages are stored in the Oracle Data Dictionary. One can detect code changes by looking at the LAST_DDL_TIME column in the USER_OBJECTS dictionary view. Example:

        SELECT OBJECT_NAME,

               TO_CHAR (CREATED,       'DD-Mon-RR HH24: MI’)

CREATE_TIME,

               TO_CHAR(LAST_DDL_TIME, 'DD-Mon-RR HH24:MI') MOD_TIME,

               STATUS

        FROM   USER_OBJECTS

        WHERE  LAST_DDL_TIME > '&CHECK_FROM_DATE';

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How can one search PL/SQL code for a string/ key value?The following query is handy if you want to know where a certain table, field or expression is referenced in your PL/SQL source code.

        SELECT TYPE, NAME, LINE

        FROM   USER_SOURCE

        WHERE  UPPER(TEXT) LIKE '%&KEYWORD%';

How can one keep a history of PL/SQL code changes?One can build a history of PL/SQL code changes by setting up an AFTER CREATE schema (or database) level trigger (available from Oracle 8.1.7). This way one can easily revert to previous code should someone make any catastrophic changes. Look at this example:

        CREATE TABLE SOURCE_HIST                     -- Create history

table

          AS SELECT SYSDATE CHANGE_DATE, USER_SOURCE.*

             FROM   USER_SOURCE WHERE 1=2;

 

        CREATE OR REPLACE TRIGGER change_hist        -- Store code in

hist table

               AFTER CREATE ON SCOTT.SCHEMA          -- Change SCOTT

to your schema name

        DECLARE

        BEGIN

          if DICTIONARY_OBJ_TYPE in ('PROCEDURE', 'FUNCTION',

                          'PACKAGE', 'PACKAGE BODY', 'TYPE') then

             -- Store old code in SOURCE_HIST table

             INSERT INTO SOURCE_HIST

                SELECT sysdate, user_source.* FROM USER_SOURCE

                WHERE  TYPE = DICTIONARY_OBJ_TYPE

                  AND  NAME = DICTIONARY_OBJ_NAME;

          end if;

        EXCEPTION

          WHEN OTHERS THEN

               raise_application_error(-20000, SQLERRM);

        END;

        /

        show errors

How can I protect my PL/SQL source code?PL/SQL V2.2, available with Oracle7.2, implements a binary wrapper for PL/SQL programs to protect the source code.

This is done via a standalone utility that transforms the PL/SQL source code into portable binary object code (somewhat larger than the original). This way you can distribute software without having to worry about exposing your proprietary

algorithms and methods. SQL*Plus and SQL*DBA will still understand and know how to execute such scripts. Just be careful, there is no “decode” command available.

The syntax is:

               wrap iname=myscript.sql oname=xxxx.plb

Can one read/write files from PL/SQL?Included in Oracle 7.3 is an UTL_FILE package that can read and write operating system files. The directory you intend writing to has to be in your INIT.ORA file (see UTL_FILE_DIR=… parameter). Before Oracle 7.3 the only means of writing a file was to use DBMS_OUTPUT with the SQL*Plus SPOOL command.

Copy this example to get started:

               DECLARE

                 fileHandler UTL_FILE.FILE_TYPE;

               BEGIN

                 fileHandler := UTL_FILE.FOPEN('/tmp', 'myfile', 'w');

                 UTL_FILE.PUTF(fileHandler, 'Look ma, I''m writing to

a file!!!\n');

                 UTL_FILE.FCLOSE(fileHandler);

               EXCEPTION

                 WHEN utl_file.invalid_path THEN

                    raise_application_error(-20000, 'ERROR: Invalid

path for file or path not in INIT.ORA.');

               END;

               /

Can one call DDL statements from PL/SQL?One can call DDL statements like CREATE, DROP, TRUNCATE, etc. from PL/SQL by using the “EXECUTE IMMEDATE” statement. Users running Oracle versions below 8i can look at the DBMS_SQL package (see FAQ about Dynamic SQL).

               begin

                  EXECUTE IMMEDIATE 'CREATE TABLE X(A DATE)';

               end;

NOTE: The DDL statement in quotes should not be terminated with a semicolon.

Can one use dynamic SQL statements from PL/SQL?Starting from Oracle8i one can use the “EXECUTE IMMEDIATE” statement to execute dynamic SQL and PL/SQL statements (statements created at run-time). Look at these examples. Note that statements are NOT terminated by semicolons:

               EXECUTE IMMEDIATE 'CREATE TABLE x (a NUMBER)';

 

               -- Using bind variables...

               sql_stmt := 'INSERT INTO dept VALUES (:1, :2, :3)';

               EXECUTE IMMEDIATE sql_stmt USING dept_id, dept_name,

location;

 

        -- Returning a cursor...

               sql_stmt := 'SELECT * FROM emp WHERE empno = :id';

               EXECUTE IMMEDIATE sql_stmt INTO emp_rec USING emp_id;

One can also use the older DBMS_SQL package (V2.1 and above) to execute dynamic statements. Look at these examples:

               CREATE OR REPLACE PROCEDURE DYNSQL AS

                 cur integer;

                 rc  integer;

               BEGIN

                 cur := DBMS_SQL.OPEN_CURSOR;

                 DBMS_SQL.PARSE(cur, 'CREATE TABLE X (Y DATE)',

DBMS_SQL.NATIVE);

                 rc := DBMS_SQL.EXECUTE(cur);

                 DBMS_SQL.CLOSE_CURSOR(cur);

               END;

               /

More complex DBMS_SQL example using bind variables:

               CREATE OR REPLACE PROCEDURE DEPARTMENTS(NO IN

DEPT.DEPTNO%TYPE) AS

                 v_cursor integer;

                 v_dname  char(20);

                 v_rows   integer;

               BEGIN

                 v_cursor := DBMS_SQL.OPEN_CURSOR;

                 DBMS_SQL.PARSE(v_cursor, 'select dname from dept

where deptno > ', DBMS_SQL.V7);

                 DBMS_SQL.BIND_VARIABLE(v_cursor, ':x', no);

                 DBMS_SQL.DEFINE_COLUMN_CHAR(v_cursor, 1, v_dname,

20);

                 v_rows := DBMS_SQL.EXECUTE(v_cursor);

                 loop

                   if DBMS_SQL.FETCH_ROWS(v_cursor) = 0 then

                      exit;

                   end if;

                   DBMS_SQL.COLUMN_VALUE_CHAR(v_cursor, 1, v_dname);

                   DBMS_OUTPUT.PUT_LINE('Deptartment name: '||

v_dname);

                 end loop;

                 DBMS_SQL.CLOSE_CURSOR(v_cursor);

               EXCEPTION

                 when others then

                      DBMS_SQL.CLOSE_CURSOR(v_cursor);

                      raise_application_error(-20000, 'Unknown

Exception Raised: '||sqlcode||' '||sqlerrm);

               END;

               /

How does one get the value of a sequence into a PL/SQL variable?As you might know, one cannot use sequences directly from PL/SQL. Oracle prohibits this:

               i := sq_sequence.NEXTVAL;

However, one can use embedded SQL statements to obtain sequence values:

               select sq_sequence.NEXTVAL into :i from dual;

How does one loop through tables in PL/SQL?Look at the following nested loop code example.

               DECLARE

                  CURSOR dept_cur IS

                  SELECT deptno

                    FROM dept

                   ORDER BY deptno;

                  -- Employee cursor all employees for a dept number

                  CURSOR emp_cur (v_dept_no DEPT.DEPTNO%TYPE) IS

                  SELECT ename

                    FROM emp

                   WHERE deptno = v_dept_no;

               BEGIN

                  FOR dept_rec IN dept_cur LOOP

                     dbms_output.put_line('Employees in Department '||

TO_CHAR(dept_rec.deptno));

                     FOR emp_rec in emp_cur(dept_rec.deptno) LOOP

                        dbms_output.put_line('...Employee is '||

emp_rec.ename);

                     END LOOP;

                 END LOOP;

               END;

               /

Is it better to put code in triggers or procedures? What is the difference?In earlier releases of Oracle it was better to put as much code as possible in procedures rather than triggers. At that stage procedures executed faster than triggers as triggers had to be re-compiled every time before executed (unless cached). In more recent releases both triggers and procedures are compiled when created (stored p-code) and one can add as much code as one likes in either procedures or triggers.

Is there a limit on the size of a PL/SQL block?

Yes, the max size is not an explicit byte limit, but related to the parse tree that is created when you compile the code. You can run the following select statement to query the size of an existing package or procedure:

               SQL> select * from dba_object_size where name =

'procedure_