PL-SQL


                      PLSQL Interview questions with answers

1. What is PL/SQL ?
Ans. PL/SQL is a procedural language that has both interactive SQL and procedural programming language constructs such as iteration, conditional branching.
2. What is the basic structure of PL/SQL ?
Ans. PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks can be used in PL/SQL.
3. What are the components of a PL/SQL block ?
Ans. A set of related declarations and procedural statements is called block.
4. What are the components of a PL/SQL Block ?
Ans.
Declarative part, Executable part and Exception part.
Datatypes PL/SQL
.
 5. What are the datatypes a available in PL/SQL ?
Ans
.
Some scalar data types such as NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN.
Some composite data types such as RECORD & TABLE.


6. What are % TYPE and % ROWTYPE ? What are the advantages of using these over datatypes?
Ans.
% TYPE provides the data type of a variable or a database column to that variable.
% ROWTYPE provides the record type that represents a entire row of a table or view or columns selected in the cursor.
The advantages are : I. Need not know about variable’s data type
ii. If the database definition of a column in a table changes, the data type of a variable changes accordingly.


7. What is difference between % ROWTYPE and TYPE RECORD ?
Ans.
% ROWTYPE is to be used whenever query returns a entire row of a table or view.
TYPE rec RECORD is to be used whenever query returns columns of different
table or views and variables.
E.g. TYPE r_emp is RECORD (eno emp.empno% type,ename emp ename %type
);
e_rec emp% ROWTYPE
cursor c1 is select empno,deptno from emp;
e_rec c1 %ROWTYPE.

8. What is PL/SQL table ?
Ans
.
Objects of type TABLE are called “PL/SQL tables”, which are modeled as (but not the same as) database tables, PL/SQL tables use a primary PL/SQL tables can have one column and a primary key.
9. What is a cursor ? Why Cursor is required ?
Ans.
Cursor is a named private SQL area from where information can be accessed. Cursors are required to process rows individually for queries returning multiple rows.
10. Explain the two type of Cursors ?
There are two types of cursors, Implicit Cursor and Explicit Cursor.PL/SQL uses Implicit Cursors for queries.
User defined cursors are called Explicit Cursors. They can be declared and used.

11. What are the PL/SQL Statements used in cursor processing ?
Ans. DECLARE CURSOR cursor name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.
12. What are the cursor attributes used in PL/SQL ?
Ans. %ISOPEN – to check whether cursor is open or not
% ROWCOUNT – number of rows fetched/updated/deleted.
% FOUND – to check whether cursor has fetched any row. True if rows are fetched.
% NOT FOUND – to check whether cursor has fetched any row. True if no rows are fetched.
These attributes are proceeded with SQL for Implicit Cursors and with Cursor name for Explicit Cursors.

13. What is a cursor for loop ?
Ans.
Cursor for loop implicitly declares %ROWTYPE as loop index, opens a cursor, fetches rows of values from active set into fields in the record and closes
when all the records have been processed.
eg. FOR emp_rec IN C1 LOOP
salary_total := salary_total +emp_rec sal;
END LOOP;
14. What will happen after commit statement ?
Ans.
Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;—–
commit;
end loop;
end; The cursor having query as SELECT …. FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT…. does not get closed even after COMMIT/ROLLBACK.

15. Explain the usage of WHERE CURRENT OF clause in cursors ?
Ans.
WHERE CURRENT OF clause in an UPDATE, DELETE statement refers to the latest row fetched from a cursor.
16. What is a database trigger ? Name some usages of database trigger ?
Ans.
Database trigger is stored PL/SQL program unit associated with a specific database table. Usages are Audit data modifications, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables.
17. How many types of database triggers can be specified on a table ? What are they ?
Ans.
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned boolean value.

18. Is it possible to use Transaction control Statements such a ROLLBACK or COMMIT in Database Trigger ? Why ?
Ans
.
It is not possible. As triggers are defined for each table, if you use COMMIT of ROLLBACK in a trigger, it affects logical transaction processing.
19. What are two virtual tables available during database trigger execution ?
Ans.
The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only available.
For triggers related to UPDATE only OLD.column_name NEW.column_name values only available.
For triggers related to DELETE only OLD.column_name values only available.

20. What happens if a procedure that updates a column of table X is called in a database trigger of the same table ?
Ans.
Mutation of table occurs
21. What is an Exception ? What are types of Exception ?
Ans.
Exception is the error handling part of PL/SQL block. The types are Predefined and user_defined. Some of Predefined exceptions are.
CURSOR_ALREADY_OPEN
DUP_VAL_ON_INDEX
NO_DATA_FOUND
TOO_MANY_ROWS
INVALID_CURSOR
INVALID_NUMBER
LOGON_DENIED
NOT_LOGGED_ON
PROGRAM-ERROR
STORAGE_ERROR
TIMEOUT_ON_RESOURCE
VALUE_ERROR
ZERO_DIVIDE
OTHERS.

22. What is Pragma EXECPTION_INIT ? Explain the usage ?
Ans.
The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error. To get an error message of a specific oracle error.
e.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number
)
23. What is Raise_application_error ?
Ans
.
Raise_application_error is a procedure of package DBMS_STANDARD which allows to issue an user_defined error messages from stored sub-program or database trigger.
24. What are the return values of functions SQLCODE and SQLERRM ?
Ans
.
SQLCODE returns the latest code of the error that has occurred.
SQLERRM returns the relevant error message of the SQLCODE.

25. Where the Pre_defined_exceptions are stored ?
Ans
. In the standard package.
26. What is a stored procedure ?
Ans.
A stored procedure is a sequence of statements that perform specific function.
27. What is difference between a PROCEDURE & FUNCTION ?
Ans.
A FUNCTION always returns a value using the return statement.
A PROCEDURE may return one or more values through parameters or may not return at all.

28. What are advantages fo Stored Procedures ?
Ans
. Extensibility, Modularity, Re-usability, Maintainability and one time compilation.
29. What are the modes of parameters that can be passed to a procedure ?
Ans.
IN, OUT, IN-OUT parameters.
30. What are the two parts of a procedure ?
Ans.
Procedure Specification and Procedure Body.
31. Give the structure of the procedure ?
Ans.
PROCEDURE name (parameter list…..)
is
local variable declarations
BEGIN
Executable statements.
Exception.
exception handlers
end;

32. Give the structure of the function ?
Ans.
FUNCTION name (argument list …..) Return datatype is
local variable declarations
Begin
executable statements
Exception
execution handlers
End;

33. Explain how procedures and functions are called in a PL/SQL block ?
Ans
.
Function is called as part of an expression.
sal := calculate_sal (‘a822′);
procedure is called as a PL/SQL statement
calculate_bonus (‘A822′);

34. What is Overloading of procedures ?
Ans.
The Same procedure name is repeated with parameters of different datatypes and parameters in different positions, varying number of parameters is called overloading of procedures.
e.g. DBMS_OUTPUT put_line
.
 35. What is a package ? What are the advantages of packages ?
Ans.
Package is a database object that groups logically related procedures.The advantages of packages are Modularity, Easier Application Design, Information. Hiding,. re-usability and Better Performance.
36.What are two parts of package ?
Ans.
The two parts of package are PACKAGE SPECIFICATION & PACKAGE BODY.
Package Specification contains declarations that are global to the packages and local to the schema.
Package Body contains actual procedures and local declaration of the procedures and cursor declarations.
37. What is difference between a Cursor declared in a procedure and Cursor declared in a package specification ?
Ans
. A cursor declared in a package specification is global and can be accessed by other procedures or procedures in a package.
A cursor declared in a procedure is local to the procedure that can not be accessed by other procedures.

38. Name the tables where characteristics of Package, procedure and functions are stored ?
Ans.
User_objects, User_Source and User_error .....
   39. Which of the following statements is true about implicit cursors?
         1. Implicit cursors are used for SQL statements that are not named.
         2. Developers should use implicit cursors with great care.
         3. Implicit cursors are used in cursor for loops to handle data processing.
         4. Implicit cursors are no longer a feature in Oracle.

   40. Which of the following is not a feature of a cursor FOR loop?
         1. Record type declaration.
         2. Opening and parsing of SQL statements.
         3. Fetches records from cursor.
         4. Requires exit condition to be defined.

   41. A developer would like to use referential datatype declaration on a variable. The variable name is EMPLOYEE_LASTNAME, and the corresponding table and column is EMPLOYEE, and LNAME, respectively. How would the developer define this variable using referential datatypes?
         1. Use employee.lname%type.
         2. Use employee.lname%rowtype.
         3. Look up datatype for EMPLOYEE column on LASTNAME table and use that.
         4. Declare it to be type LONG.

   42. Which three of the following are implicit cursor attributes?
         1. %found
         2. %too_many_rows
         3. %notfound
         4. %rowcount

         5. %rowtype

   43. If left out, which of the following would cause an infinite loop to occur in a simple loop?
         1. LOOP
         2. END LOOP
         3. IF-THEN
         4. EXIT

   44. Which line in the following statement will produce an error?
         1. cursor action_cursor is
         2. select name, rate, action
         3. into action_record
         4. from action_table;
         5. There are no errors in this statement.

   45. The command used to open a CURSOR FOR loop is
         1. open
         2. fetch
         3. parse
         4. None, cursor for loops handle cursor opening implicitly.

   46. What happens when rows are found using a FETCH statement
         1. It causes the cursor to close
         2. It causes the cursor to open
         3. It loads the current row values into variables
         4. It creates the variables to hold the current row values

   47. Read the following code:
          CREATE OR REPLACE PROCEDURE find_cpt
          (v_movie_id {Argument Mode} NUMBER, v_cost_per_ticket {argument mode} NUMBER)
          IS
          BEGIN
            IF v_cost_per_ticket  > 8.5 THEN
          SELECT  cost_per_ticket
          INTO            v_cost_per_ticket
          FROM            gross_receipt
          WHERE   movie_id = v_movie_id;
            END IF;
          END;
      Which mode should be used for V_COST_PER_TICKET?

         1. IN
         2. OUT
         3. RETURN
         4. IN OUT

  48. Read the following code:
          CREATE OR REPLACE TRIGGER update_show_gross
                {trigger information}
               BEGIN
                {additional code}
               END;
      The trigger code should only execute when the column, COST_PER_TICKET, is greater than $3. Which trigger information will you add?

         1. WHEN (new.cost_per_ticket > 3.75)
         2. WHEN (:new.cost_per_ticket > 3.75
         3. WHERE (new.cost_per_ticket > 3.75)
         4. WHERE (:new.cost_per_ticket > 3.75)

  49. What is the maximum number of handlers processed before the PL/SQL block is exited when an exception occurs?
         1. Only one
         2. All that apply
         3. All referenced
         4. None

  50. For which trigger timing can you reference the NEW and OLD qualifiers?
         1. Statement and Row
         2. Statement only
         3. Row only
         4. Oracle Forms trigger

  13. Read the following code:
          CREATE OR REPLACE FUNCTION get_budget(v_studio_id IN NUMBER)
          RETURN number IS
          v_yearly_budget NUMBER;
          BEGIN
                 SELECT  yearly_budget
                 INTO            v_yearly_budget
                 FROM            studio
                 WHERE   id = v_studio_id;
                 RETURN v_yearly_budget;
          END;
      Which set of statements will successfully invoke this function within SQL*Plus?

         1. VARIABLE g_yearly_budget NUMBER
            EXECUTE g_yearly_budget := GET_BUDGET(11);

         2. VARIABLE g_yearly_budget NUMBER
            EXECUTE :g_yearly_budget := GET_BUDGET(11);
         3. VARIABLE :g_yearly_budget NUMBER
            EXECUTE :g_yearly_budget := GET_BUDGET(11);
         4. VARIABLE g_yearly_budget NUMBER
            :g_yearly_budget := GET_BUDGET(11);

  14. CREATE OR REPLACE PROCEDURE update_theater
          (v_name IN VARCHAR v_theater_id IN NUMBER) IS
          BEGIN
                 UPDATE  theater
                 SET             name = v_name
                 WHERE   id = v_theater_id;
          END update_theater;
      When invoking this procedure, you encounter the error:
          ORA-000: Unique constraint(SCOTT.THEATER_NAME_UK) violated.
      How should you modify the function to handle this error?

         1. An user defined exception must be declared and associated with the error code and handled in the EXCEPTION section.
         2. Handle the error in EXCEPTION section by referencing the error code directly.
         3. Handle the error in the EXCEPTION section by referencing the UNIQUE_ERROR predefined exception.
         4. Check for success by checking the value of SQL%FOUND immediately after the UPDATE statement.

  15. Read the following code:

CREATE OR REPLACE PROCEDURE calculate_budget IS
          v_budget studio.yearly_budget%TYPE;
          BEGIN
                 v_budget := get_budget(11);
                 IF v_budget < 30000
                  THEN
                         set_budget(11,30000000);
                 END IF;
          END;
      You are about to add an argument to CALCULATE_BUDGET. What effect will this have?

         1. The GET_BUDGET function will be marked invalid and must be recompiled before the next execution.
         2. The SET_BUDGET function will be marked invalid and must be recompiled before the next execution.
         3. Only the CALCULATE_BUDGET procedure needs to be recompiled.
         4. All three procedures are marked invalid and must be recompiled.

  16. Which procedure can be used to create a customized error message?
         1. RAISE_ERROR
         2. SQLERRM
         3. RAISE_APPLICATION_ERROR
         4. RAISE_SERVER_ERROR

  17. The CHECK_THEATER trigger of the THEATER table has been disabled. Which command can you issue to enable this trigger?
         1. ALTER TRIGGER check_theater ENABLE;
         2. ENABLE TRIGGER check_theater;
         3. ALTER TABLE check_theater ENABLE check_theater;
         4. ENABLE check_theater;

  18. Examine this database trigger
          CREATE OR REPLACE TRIGGER prevent_gross_modification
          {additional trigger information}
          BEGIN
                 IF TO_CHAR(sysdate, DY) = MON
            THEN
            RAISE_APPLICATION_ERROR(-20000,Gross receipts cannot be deleted on Monday);
                 END IF;
          END;
      This trigger must fire before each DELETE of the GROSS_RECEIPT table. It should fire only once for the entire DELETE statement. What additional information must you add?

         1. BEFORE DELETE ON gross_receipt
         2. AFTER DELETE ON gross_receipt
         3. BEFORE (gross_receipt DELETE)
         4. FOR EACH ROW DELETED FROM gross_receipt

  19. Examine this function:
          CREATE OR REPLACE FUNCTION set_budget
          (v_studio_id IN NUMBER, v_new_budget IN NUMBER) IS
          BEGIN
                 UPDATE  studio
                 SET             yearly_budget = v_new_budget
                 WHERE   id = v_studio_id;
                 IF SQL%FOUND THEN
                         RETURN TRUEl;
                 ELSE
                         RETURN FALSE;
                 END IF;
                  COMMIT;
          END;
      Which code must be added to successfully compile this function?

         1. Add RETURN right before the IS keyword.
         2. Add RETURN number right before the IS keyword.
         3. Add RETURN boolean right after the IS keyword.
         4. Add RETURN boolean right before the IS keyword.

  20. Under which circumstance must you recompile the package body after recompiling the package specification?
         1. Altering the argument list of one of the package constructs
         2. Any change made to one of the package constructs
         3. Any SQL statement change made to one of the package constructs.
         4. Removing a local variable from the DECLARE section of one of the package constructs

  21. Procedure and Functions are explicitly executed. This is different from a database trigger. When is a database trigger executed?
         1. When the transaction is committed
         2. During the data manipulation statement
         3. When an Oracle supplied package references the trigger
         4. During a data manipulation statement and when the transaction is committed .

  22. Which Oracle supplied package can you use to output values and messages from database triggers, stored procedures and functions within SQL*Plus?
         1. DBMS_DISPLAY
         2. DBMS_OUTPUT
         3. DBMS_LIST
         4. DBMS_DESCRIBE

  23. What occurs if a procedure or function terminates with failure without being handled?
         1. Any DML statements issued by the construct are still pending and can be committed or rolled back.
         2. Any DML statements issued by the construct are committed
         3. Unless a GOTO statement is used to continue processing within the BEGIN section, the construct terminates.
         4. The construct rolls back any DML statements issued and returns the unhandled exception to the calling environment.

  24. Examine this code
          BEGIN
                 theater_pck.v_total_seats_sold_overall := theater_pck.get_total_for_year;
          END;  For this code to be successful, what must be true?

         1. Both the V_TOTAL_SEATS_SOLD_OVERALL variable and the GET_TOTAL_FOR_YEAR function must exist only in the body of the THEATER_PCK package.
         2. Only the GET_TOTAL_FOR_YEAR variable must exist in the specification of the THEATER_PCK package.
         3. Only the V_TOTAL_SEATS_SOLD_OVERALL variable must exist in the specification of the THEATER_PCK package.
         4. Both the V_TOTAL_SEATS_SOLD_OVERALL variable and the GET_TOTAL_FOR_YEAR function must exist in the specification of the THEATER_PCK package.

  25. A stored function must return a value based on conditions that are determined at runtime. Therefore, the SELECT statement cannot be hard-coded and must be created dynamically when the function is executed. Which Oracle supplied package will enable this feature?
         1. DBMS_DDL
         2. DBMS_DML
         3. DBMS_SYN
         4. DBMS_SQL
                     

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