SQL Interview Questions

1. The most important DDL statements in SQL are:CREATE TABLE - creates a new database tableALTER TABLE - alters (changes) a database tableDROP TABLE - deletes a database tableTRUNCATE - cleans all dataRENAME- renames a table name

2. Operators used in SELECT statements.= Equal or != Not equal> Greater than= Greater than or equal 8.5 THEN15. SELECT cost_per_ticket16. INTO v_cost_per_ticket17. FROM gross_receipt18. WHERE movie_id = v_movie_id;19. END IF;20. END;Which mode should be used for V_COST_PER_TICKET?1. IN2. OUT3. RETURN4. IN OUT73. Read the following code:22. CREATE OR REPLACE TRIGGER update_show_gross23. {trigger information}24. BEGIN25. {additional code}26. 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 > 3.753. WHERE (new.cost_per_ticket > 3.75)4. WHERE (:new.cost_per_ticket > 3.75)

74. What is the maximum number of handlers processed before the PL/SQL block is exited when an exception occurs?1. Only one2. All that apply3. All referenced4. None

77. 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

78. Read the following code:CREATE OR REPLACE FUNCTION get_budget(v_studio_id IN NUMBER)RETURN number ISv_yearly_budget NUMBER;BEGINSELECT yearly_budgetINTO v_yearly_budgetFROM studioWHERE 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 NUMBEREXECUTE g_yearly_budget := GET_BUDGET(11);2. VARIABLE g_yearly_budget NUMBEREXECUTE :g_yearly_budget := GET_BUDGET(11);3. VARIABLE :g_yearly_budget NUMBEREXECUTE :g_yearly_budget := GET_BUDGET(11);4. VARIABLE g_yearly_budget NUMBER31. CREATE OR REPLACE PROCEDURE update_theater32. (v_name IN VARCHAR v_theater_id IN NUMBER) IS33. BEGIN34. UPDATE theater35. SET name = v_name36. WHERE id = v_theater_id;37. END update_theater;

79. 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 associatedwith the error code and handled in the EXCEPTION section.2. Handle the error in EXCEPTION section by referencing the errorcode 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.

80. Read the following code:40. CREATE OR REPLACE PROCEDURE calculate_budget IS41. v_budget studio.yearly_budget%TYPE;42. BEGIN43. v_budget := get_budget(11);44. IF v_budget < 3000045. THEN46. set_budget(11,30000000);47. END IF;48. 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.

81. Which procedure can be used to create a customized error message?1. RAISE_ERROR2. SQLERRM3. RAISE_APPLICATION_ERROR4. RAISE_SERVER_ERROR

82. 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;

83. Examine this database trigger52. CREATE OR REPLACE TRIGGER prevent_gross_modification53. {additional trigger information}54. BEGIN55. IF TO_CHAR(sysdate, DY) = MON56. THEN57. RAISE_APPLICATION_ERROR(-20000,Gross receipts cannot be deleted on Monday);58. END IF;59. 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_receipt2. AFTER DELETE ON gross_receipt3. BEFORE (gross_receipt DELETE)4. FOR EACH ROW DELETED FROM gross_receipt

84. Examine this function:61. CREATE OR REPLACE FUNCTION set_budget62. (v_studio_id IN NUMBER, v_new_budget IN NUMBER) IS63. BEGIN64. UPDATE studio65. 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.

85. Under which circumstance must you recompile the package body after recompiling the package specification?1. Altering the argument list of one of the package constructs2. Any change made to one of the package constructs3. Any SQL statement change made to one of the package constructs4. Removing a local variable from the DECLARE section of one of the package constructs

86. Procedure and Functions are explicitly executed. This is different from a database trigger. When is a database trigger executed?1. When the transaction is committed2. During the data manipulation statement3. When an Oracle supplied package references the trigger4. During a data manipulation statement and when the transaction is committed

87. Which Oracle supplied package can you use to output values and messages from database triggers, stored procedures and functions within SQL*Plus?1. DBMS_DISPLAY2. DBMS_OUTPUT3. DBMS_LIST4. DBMS_DESCRIBE

88. 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 committed3. 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.

89. Examine this code71. BEGIN72. theater_pck.v_total_seats_sold_overall := theater_pck.get_total_for_year;73. 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.

90. 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_DDL2. DBMS_DML3. DBMS_SYN4. DBMS_SQL

91 How to implement ISNUMERIC function in SQL *Plus ? Method1: Select length (translate(trim (column_name),'+-.0123456789',''))from dual; Will give you a zero if it is a number or greater than zero if not numeric (actually gives the count of non numeric characters) Method 2: select instr(translate('wwww','abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ','XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXX'),'X') FROM dual; It returns 0 if it is a number, 1 if it is not.

92 How to Select last N records from a Table? select * from (select rownum a, CLASS_CODE,CLASS_DESC from clm) where a > ( select (max(rownum)-10) from clm) Here N = 10The following query has a Problem of performance in the execution of the followingquery where the table ter.ter_master have 22231 records. So the results are obtainedafter hours.Cursor rem_master(brepno VARCHAR2) ISselect a.* from ter.ter_master awhere NOT a.repno in (select repno from ermast) and(brepno = 'ALL' or a.repno > brepno)Order by a.repnoWhat are steps required tuning this query to improve its performance?-Have an index on TER_MASTER.REPNO and one on ERMAST.REPNO-Be sure to get familiar with EXPLAIN PLAN. This can help you determine the executionpath that Oracle takes. If you are using Cost Based Optimizer mode, then be sure thatyour statistics on TER_MASTER are up-to-date. -Also, you can change your SQL to:SELECT a.*FROM ter.ter_master aWHERE NOT EXISTS (SELECT b.repno FROM ermast bWHERE a.repno=b.repno) AND(a.brepno = 'ALL' or a.repno > a.brepno)ORDER BY a.repno;

93. What is the difference between Truncate and Delete interms of Referential Integrity?DELETE removes one or more records in a table, checking referential Constraints (to see if there are dependent child records) and firing any DELETE triggers. In the order you are deleting (child first then parent) There will be no problems.TRUNCATE removes ALL records in a table. It does not execute any triggers. Also, itonly checks for the existence (and status) of another foreign key Pointing to thetable. If one exists and is enabled, then you will get The following error. Thisis true even if you do the child tables first.ORA-02266: unique/primary keys in table referenced by enabled foreign keysYou should disable the foreign key constraints in the child tables before issuingthe TRUNCATE command, then re-enable them afterwards.

PL-SQL Interview Questions

1. Describe the difference between a procedure, function and anonymous pl/sql block.Level: LowExpected answer : Candidate should mention use of DECLARE statement, a function mustreturn a value while a procedure doesn?t have to.

2. What is a mutating table error and how can you get around it?Level: IntermediateExpected answer: This happens with triggers. It occurs because the trigger is tryingto update a row it is currently using. The usual fix involves either use of viewsor temporary tables so the database is selecting from one while updating the other.

3. Describe the use of %ROWTYPE and %TYPE in PL/SQLLevel: LowExpected answer: %ROWTYPE allows you to associate a variable with an entire table row.The %TYPE associates a variable with a single column type.

4. What packages (if any) has Oracle provided for use by developers?Expected answer: Oracle provides the DBMS_ series of packages. There are manywhich developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION,DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. Ifthey can mention a few of these and describe how they used them, even better. Ifthey include the SQL routines provided by Oracle, great, but not really whatwas asked.

5. Describe the use of PL/SQL tablesExpected answer: PL/SQL tables are scalar arrays that can be referenced by abinary integer. They can be used to hold values for use in later queriesor calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation,or RECORD.

6. When is a declare statement needed ?The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used.

7. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the NOTFOUND cursor variable in the exit when statement? Why?Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.

8. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?Expected answer: SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.

9. How can you find within a PL/SQL block, if a cursor is open?Expected answer: Use the %ISOPEN cursor status variable.

10. How can you generate debugging output from PL/SQL?Expected answer: Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE canalso be used.

11. What are the types of triggers?Expected Answer: There are 12 types of triggers in PL/SQL that consist ofcombinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE andALL key words:BEFORE ALL ROW INSERTAFTER ALL ROW INSERTBEFORE INSERTAFTER INSERT etc.

SQL / SQLPlus Interview Questions

1. How can variables be passed to a SQL routine?Expected answer: By use of the & symbol. For passing in variables the numbers1-8 can be used (&1, &2,...,&8) to pass the values after the command into theSQLPLUS session. To be prompted for a specific variable, place the ampersandedvariable in the code itself:"select * from dba_tables where owner=&owner_name;" . Use of doubleampersands tells SQLPLUS to resubstitute the value for each subsequentuse of the variable, a single ampersand will cause a reprompt for thevalue unless an ACCEPT statement is used to get the value from the user.

2. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this?Expected answer: The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the concatenation function "". Another method, although it is hard to document and isn?t always portable is to use the return/linefeed as a part of a quoted string.

3. How can you call a PL/SQL procedure from SQL?Expected answer: By use of the EXECUTE (short form EXEC) command.

4. How do you execute a host operating system command from within SQL?Expected answer: By use of the exclamation point "!" (in UNIX and some other OS) or the HOST (HO) command.

5. You want to use SQL to build SQL, what is this called and give an exampleExpected answer: This is called dynamic SQL. An example would be:set lines 90 pages 0 termout off feedback off verify offspool drop_all.sqlselect ?drop user ?username? cascade;? from dba_userswhere username not in ("SYS?,?SYSTEM?);spool offEssentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ?? the values selected from the database.

6. What SQLPlus command is used to format output from a select?Expected answer: This is best done with the COLUMN command.

7. You want to group the following set of select returns, what can you group on?Max(sum_of_cost), min(sum_of_cost), count(item_no), item_noExpected answer: The only column that can be grouped on is the "item_no" column, the rest have aggregate functions associated with them.

8. What special Oracle feature allows you to specify how the cost based system treats a SQL statement?Level: Intermediate to high Expected answer: The COST based system allows the use of HINTs to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.

9. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done?Level: High Expected answer: Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example: select rowid from emp e where e.rowid > (select min(x.rowid) from emp x where x.emp_no = e.emp_no); In the situation where multiple columns make up the proposed key, they must all be used in the where clause.

10. What is a Cartesian product?Expected answer: A Cartesian product is the result of an unrestricted join of two or more tables. The result set of a three table Cartesian product will have x * y * z number of rows where x, y, z correspond to the number of rows in each table involved in the join.

11. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic?Level: High Expected answer: Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across.

12. What is the default ordering of an ORDER BY clause in a SELECT statement?Expected answer: Ascending

13. What is tkprof and how is it used?Level: Intermediate to high Expected answer: The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.

14. What is explain plan and how is it used?Level: Intermediate to high Expected answer: The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof.

15. How do you set the number of lines on a page of output? The width?Level: Low Expected answer: The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.

16. How do you prevent output from coming to the screen?Level: LowExpected answer: The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turnsoff screen output. This option can be shortened to TERM.

17. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?Level: Low Expected answer: The SET options FEEDBACK and VERIFY can be set to OFF.

18. How do you generate file output from SQL?Answer: By use of the SPOOL commandPosted bySunil Duttat1:29 AM1 comment:Links to this postThursday, September 11, 2008Customer Interface DiagramCustomer Interface Diagram

Posted bySunil Duttat3:24 AM2 comments:Links to this postMaster Detail Forms

1) Create Two Tables (With Parent / Child relationships)

a) Create table orders(order_no number(10),custoner varchar2(20),order_date date)/b) Create table lines( line_no number(10),order_no number(10),item varchar2(20),qty number(10),price number(10),amount number(10))/

2) Alter the table structures and primary and foreign keysAlter table orders add constraint orders_pk primary key (order_no);Alter table lines add constraint lines_fk foreign key (order_no) references orders (order_no);

3) Create public synonyms for the tables.4) Register two tables with constraints information.5) Open form builder software.6) Open template.fmb file.7) Save as TETMADET.fmb8) Change form module name as form name.9) Delete default blocks , canvasses and windows.10) Create two windows , two canvassesWindow1 : OrdersWindow2 : LinesCanvas1 : OrdersCanvas2 : Lines

11) Assign Canvasses to Windows.12) Assign Windows to Canvasses.13) Assign property classes to windows and canvasses.14) Create Two BlocksBlock1 : Orders Type : FormBlock2 : Lines Type : Tabular No of Records : 5

15) Define master detail block relationship between two blocks .Relationship Name : Orders_Lines

16) Create a Control Block17) Create a Check box on detail window/ detail canvasBlock => ControlName => Orders_lines (Same as your master detail relationship name)Checked value => ImmediateUnchecked Value => DeferredDefault => Immediate

18) Create a Push button in Master Window / Master CanvasName : LINESLabel : Lines ..Block => Control

19) Assign Text Item property class to all text items on Orders and Lines block.20) Set Module / Form Level propertiesFirst navigation data block => OrdersConsole Window => Orders

21) Modify App_custom PackageClose window procedureIf ( wnd = Orders) thenApp_window.close_first_window;Elsif (wnd = Lines) thenApp_window.set_coordination(WHEN-WINDOW-CLOSED, :CONTROL.ORDER_LINES (CHECKBOX) , ORDERS_LINES (RELATIONSHIP NAME) );End if;

Open Window ProcedureIf (wnd = Orders) thenGo_block ( Orders) ;Return;If (wnd = Lines) thenApp_window.set_coordination ( OPEN-WINDOW, :CONTROL,ORDERS_LINES , ORDERS_LINES);Go_block ( Lines);End if;

22) Create a program unitName : ControlType : Package SpecProcedure Lines (Event In Varchar2) ;Procedure Orders_Lines ( Event In Varchar2);

23) Create a program unitName : ControlType : Package BodyProcedure Lines (Event In Varchar2) isBeginIf (event = WHEN BUTTON PRESSED ) thenApp_custom.open_window (Lines);Return;End if;End Lines;

Procedure Orders_Lines ( Event In Varchar2) thenBeginIf (Event = WHEN CHECKBOX CHANGED) thenEnd if ;End order_lines;

24) In control block write a WBP trigger on Lines Button.Control . Lines ( WHEN BUTTON PRESSED);

25) In control block write a WCC trigger on Orders_Lines checkbox.Control.orders_lines(WHEN- CHECKBOX CHANGED);

26) Modify PRE FORM triggerAPP_WINDOW.SET_WINDOW_POSITION(ORDERS,NULL,ORDERS);

27) Save and Compile .28) Register the form.Posted bySunil Duttat3:13 AM1 comment:Links to this postCUSTOM FORM DEVELOPMENT

On the CLIENT machine create a FOLDER as say: c:\custom_sunil

In custom_sunil folder creates 2 folders forms, resource

Copy TEMPLATE.fmb, APPSTAND.fmb, .pll files to CLIENT

Copy TEMPLATE.fmb , APPSTAND.fmb from AU_TOP/forms/US to c:\custom_sunil\ forms directory copy all .pll files from /Applvis/visappl/au/11.5.0/resource to c:\custom_sunil\resource using ftp On windows go to command prompt Cd c:\custom_sunil\forms ftp cloneserver username: applmgr password: applmgr now you are at ftp prompt bin prompt cd visappl/au/11.5.0/forms/US ( here apparently cd $AU_TOP does not work) get TEMPLATE.fmb (file copied) get APPSTAND.fmb (file copied) lcd ./resource (check this. Basically you need to be in c:\custom_sunil\resource. You can go to that directory and then run ftp) cd visappl/au/11.5.0/resource mget *.pll ( now all .pll files are copied to c:custom_sunil/resource)

SET env variable FORMS60_PATH through regedit

Regedit/HKEY_LOCAL_MACHINE/software/oracle Double click FORMS60_PATH At the end of existing value data add: ;c:\custom_sunil\froms;c:\custom_sunil\resource

Now open TEMPLATE.fmb and make the following changes

DELETE BLOCKNAME &DETAIL BLOCK FROM DATABLOCK,DELETE BLOCKNAME FROM CANVAS AND WINDOW Create a window NEW_WIN, canvas NEW_CAN Create a new block based on the table you created in your custom schema In pre-form trigger: app_windows.set_window_position(NEW_WIN). In program units open custom_package.AP_cutom_pacakge body Change : if (wind=NEW_WIN); Template name = SUNIL_FORM Save as SUNIL_FROM to c:\custom_sunil\forms (????????SET THE WINDOW NAME AS U HAVE CREATED NEW WINDOW IN PRE-FORM TRIGGER BY BLOCKNAME?????)

DEPLOY the FORM (upload it to AU_TOP/forms/US)

Go to command prompt (on client) cd c:\cutom_sunil\forms ftp cloneserver cd visappl/au/11.5.0/froms/US bin prompt put SUNIL_FORM.fmb

Changing ORACLE_HOME (/Visdb/visdb/9.2.0 to /Applvis/visora/8.0.6)

thru putty login as applmgr pwd: /Applvis echo $ORACLE_HOME: shows /Visdb/visdb/9.2.0 cd visora cd 8.0.6 . VIS_cloneserver.env (this changes ORACLE_HOME apparently based on pwd?) echo $ORACLE_HOME: shows /Applvis/visora/8.0.6 now ORACLE_HOME is 8.0.6 (forms/reports home) pwd : gives /Applvis/visora/8.0.6

COMPILE and generate FMX

(now you are in /Applvis/visora/8.0.6 directory and ORACLE_HOME is set to /Applvis/visora/8.0.6) pwd: gives /Applvis/visora/8.0.6 f60gen module=$AU_TOP/forms/US/SUNIL_FORMS.fmb module_type=form user=apps output_file=$SUNIL_TOP/forms/US/SRIN_FORM.fmx compile_all=special batch=no this generates SUNIL_FORM.fmx and puts in SUNIL_TOP/forms/US

FORM REGISTRATION

Login to applications with application developer responsibility Application/form Enter the following detailso Form: the fmx name (SUNIL_FORM)o Application: Oracle Receivables (as per Amer) give appropriate name based the intended use of this formo user form name: SUNIL_FORM_U (this will appear in LOV)o SAVE

Attach the FORM to FUNCTION(Create a new function)Application/functionEnter the following detailso Function: SUNIL_FUNCTo User function name: SUNIL FUNCTIONo Form: SUNIL_FORM (previously registered)o SAVE

Attach FUNCTION to MENUApplication/menu Enter the following detailso Menu: sunil_menuo User menu name: sunil menuo Seq: 1o Prompt: sunil formo Function: SUNIL_FUNCT( previously deined)o SAVE

Attach MENU to RESPONSIBILITY

Attach RESPONSIBILITY to USER

Login as the new USER

See the formPosted bySunil Duttat3:03 AM7 comments:Links to this postWednesday, September 10, 2008TRIGGERS

TRIGGERS

IT IS A PL/SQL BLOCK OR PL/SQL PROCEDURE ASOCITED WITH A TABLE,VIEW,SCHEMA OR DATABASE EXECUTED AUTOMATICALLY RATHER IN TECHNICAL TERMS IMPLICITLY FIRED AUTOMATICALLY WHENEVER A SPECIFIC EVENT OCCURS UPON THE OBJECT ASSOCIAYED WITH.

TYPES OF TRIGGERS

THERE ARE TWO TYPES OF TRIGGERS.

APPLICATION TRIGGER:-FIRED WHENEVER AN EVENT //CAN BE CONSIDERED AS A DML OPERATION// OCCURS UPON A PARTICULAR APPLICATION.

DATABASE TRIGGER:-FIRED WHENVER AN EVENT (IN THE SENSE ANY DML OPERATION OR ANY SYSTEM EVENT I.E LOGON OR SHUTDOWN) OCCURS ON A SCHEMA OR DATABASE.THESE ARE FIRED IMPLICITLY

INSTEAD OF TRIGGERS

THESE ARE ONLY LIMITED TO THE VIEWS .THE NAME SIGNIFIES THE OPERATION OF THE TRIGGER.TO BE MORE ELABORATIVE WHENEVER A DML IS OPERATED UPON A VIEW THE ACTION IS TAKEN CARE OF BY THE INSTEAD OF TRIGGER.RATHER IF ANY OTHER TRIGGERS ARE ASSOCIATED WITH THAT TABLE THEN THOSE TRIGGER WILL BE FIRED.

WHY THE TRIGGERS ARE DESIGNED?

FOR RELATED TASKS TO BE PERFORMED AND TO CENTRALIZE THE GLOBAL OPERATIONS WHICH TAKES CARE OF THE ACTIONS RATHER CONSIDERING WHATEVER APPLIACTION OR WHOEVER THE USER MAY BE.

CREATING DML TRIGGERS

A TRIGGER CONTAINS

A) TRIGGER TIMING DESCRIBES ABOUT THE FIRING OF THE TRIGGER WRT TRIGGERING EVENT.B) TRIGGERING EVENT DESCRIBES ABOUT THE DML WHICH IS TO BE TAKEN CARE FOR THE BY ACTIONS TO BE RAISED.C) TRIGGER TYPE DESCRIBES ABOUT THE NUMBER OF TIMES OF EXECUTION OF TRIGGER.D) TRIGGER BODY DESCRIBES ABOUT THE ACTIONS TAKEN CARE OF BY THE TRIBGGER.DML TRGGER COMPONENTS

TRIGGER TIMING

A) BEFORE TRIGGERS EXECUTION OF TRIGGER BOBY OCCURS BEFORE THE DML EVENT IS OPERATED UPON AN OBJECT.B) AFTER TRIGGERS EXECUTION OF TRIGGER BOBY OCCURS AFTER THE DML EVENT IS OPERATED UPON AN OBJECT.C) INSTEAD OF SPECIFIES A SEPARATE EXECUTION PROCESS APART FROM THE TRIGGERING STATEMENT.THESE ACT UPON THE VIEWS AND ARE NOT MODIFIABLE.

DESCRIPTIONS

BEFORE TRIGGERS ARE USED TO DETERMINE THE STATUS OF TRIGGER STATEMENT WHETHER TO BE COMPLETED.ALSO BETTER EXPLANATION CAN BE ROLLBACK.ALSO TO FETCH THE COLUMN VALUES PRIOR TO EXECUTION AND TO VALIDATE RULES OF BUSINESS.

AFTER TRIGGERS ARE USED TO COMPLETE THE ACTON BEFORE TRIGGERING ACTION.IF THERE IS A PRESENCE OF A BEFORE TRIGGER THEN TO INITIATE A DIFFERENT ACTION.

INSTEAD OF TRIGGERS ARE USED TO MODIFY THE VIEWS WHICH CANNOT BE MODIFIED BY A SQL DML STATEMENT DUE TO LACK OF MODIFICATION INHERITANCE.THESE WORK IN THE BACKGROUND ACCORDING TO THE DML ACTIONS SPECIFIED IN THE TRIGGERING BODY.

TRIGGERING EVENTS CAN BE SPECIFICALLY LINKED WITH THE DMLS SUCH AS INSERT, UPDATE OR A DELETE.IN CASE OF UPDATE DML THE COLUMN LIST ARE TO SPECIFIED FOR WHICH THE TRIGGERING ACTIONS ARE TO BE TAKEN CARE OF.

TRIGGER TYPE SPECIFIES WHETHER THE TRIGGER IS TO BE FIRED FOR EACH ROW OR FOR MULTIPLE ROWS (STATEMENT TRIGGERS).THERE ARE TWO TYPES OF TRIGGERS.

1) ROW TRIGGERS ARE EXECUTED ONCE FOR EACH ROW RETRIEVED BY THE DML SPECIFIED IN THE STATEMENT.IT IS NOT EXECUTED IF THE STATEMENT DOES NOT RETURN ANY VALUE.IT IS NOT EXECUTED WHEN NO ROWS ARE SELECTED.

2) STATEMENT TRIGGER IS FIRED ONCE ON BEHALF OF THE TRIGGERING EVENT EVEN IF NO ROWS ARE AFFECTED AT ALL.

TRIGGER BODY EXPLAINS ABOUT THE ACTIONS TO BE TAKEN CARE OF BY THE TRIGGER.IT CAN BE PL/SQL BLOCK OR A CALL PROCEDURE.

NOTE1) WHEN THE TRIGGERING DATA MANIPULATION STATEMENT EFFECTS THE A SINGLE ROW, BOTH THE ROW TRIGGER AND STATEMENT TRIGGER FIRE EXACTLY ONCE PROVIDED THE TYPE OF TRIGGER THAT HAS BEEN MENTIONED IN THE TRIGGER BODY.

2) WHEN A TRIGGERING DATA MANIPULATION STATEMENT AFFECTS MULTIPLE ROWS THEN THE STATEMENT TRIGGER FIRES EXACTLY ONCE AND THE ROW TRIGGER FIRES ONCE FOR EVERY ROWEFFECTED BY THE STATEMENT.

SYNTAXCREATE TRIGGERTIMINGEVENT1 ORORON

TRIGGER NAME SHOULD BE UNIQUE COMPARED TO OTHER TRIGGERS.

SPECIFIES THE TIME WHEN THE TRIGGER WILL FIREEITHEROR

IDENTIFIES THE DML THAT CAUSES THE TRIGGER TO FIRE.EITHER,,OR ALL OF THE THREE.NAME OF THE TABLE ASSOCIATED WITH THE TRIGGER.

EXPLAINS ABOUT THE ACTIONS PERFORMED.IT BEGINS WITH A DECALERE AND END OR A CALL OF PROCEDURE.

USING COLUMNS NAMES WITH UPDATE TRIGGERS INCREASE THE PERFORMANCE BECAUSE THE TRIGGER IS FIRED ONLY WHEN THE UPDATION OF CONCERNED COLUMN OCCURS.IT IS NO WHERE CONCERNNED WITH THE UPDATION OF ANY OTHER COLUMNS OF THE DESCRIBED TABLE IN THE TRIGGER.

EXAMPLE:

IN THE DESCRIBED TRIGGER WHICH IMPLEMENTS THE BUSSINESS RULES THAT RESTRICTS THE ACCESS OF DATABASE TABLE AFTER THE OFFICE HOURS AND HOLIDAYS PROVIDED THE WORK DAY CALENDER IS 5 DAYS A WEEK.

CREATE OR REPLACE TRIGGER SECURE_EMPLOYEESBEFORE INSERT OR DELETE OR UPDATE ON EMPLOYEESBEGINIF (TO_CHAR (SYSDATE,DY) IN (SAT,SUN)) OR(TO_CHAR (SYSDATE,HH24) NOT BETWEEN 08 AND 18)THENIF INSERTING THENRAISE_APPLICATION_ERROR (-20500,UR STATEMENT);ELSIF DELETING THENRAISE_APPLICATION_ERROR (-20500,UR STATEMENT);ELSIF UPDATING THENRAISE_APPLICATION_ERROR (-20500,UR STATEMENT);ELSERAISE_APPLICATION_ERROR (-20500,UR SATAMENT2);END IF;END IF;END;

DML ROW TRIGGERS

WE HAVE TO SPECIFY A SPECIAL PHRASE FOR INITIATING A ROW TRIGGER.REFERENING TO THE ABOVE MENTIONED SYNTAX OF TRIGGER AFTER THE TABLE NAME FOR EACH ROW PHRASE IF SPECIFIED INDICATES THE TRIGGER TO BE A ROW TRIGGER.HERE THE NEW VALUES AND THE OLD VALUES ARE ALSO REFERED FOR CORELATION BETWEEN THE OLD VALUES AND NEW VALUES.

WE CAN ALSO RESTRICT THE FIRING OF A ROW TRIGGER BY SPECIFING A WHEN CLAUSE AFTER THE PHRASE MENTIONED ABOVE.

EXAMPLE

CREATE OR REPLACE TRIGGER RESTRICT_SALARYBEFORE INSERT OR UPDATE OF SALARY ON EMPLOYEESFOR EACH ROWBEGINIF NOT (:NEW.JOB_ID IN (AD_PRES,AD_VP))AND (:NEW.SALARY) > 15000THENRAISE_APPLICATION_ERROR (-20500,)END IF;END;

EXPALAINATION

FOR AN UPDATE OR INSERT UPON EMPLOYEES TABLE IF THE JOB_ID SPECIED IS OTHER THAN AD_PRES AND AD_VP AND SALARY SPECIFIED IS GREATER THAN 15000 IN THE CASE TRIGGER IS FIRED.IN STRAIGHT EAPLAINTION THE EMPLOYEES WHICH HAVE A JOB_ID OF AD_PRES AND AD_VP CAN ONLY EARN A SALARY GREATER THAN 15000.

RESTRICTING A ROW TRIGGER

CREATE OR REPLACE TRIGGER RESTRICT_SALARYBEFORE INSERT OR UPDATE OF SALARY ON EMPLOYEESFOR EACH ROWWHEN (NEW.JOB_ID = SA_REP)BEGINIF INSERTING THEN: NEW .COMMISSION_PCT:= 0;ELSIF (:OLD.COMMISSION_PCT) IS NULL THEN: NEW.COMMISSION_PCT:= 0;ELSE: NEW.COMMISSION_PCT:=:OLD.COMMISSION_PCT + 0.05;END IF;END;

EXPLAINATION

IF AN INSERT OPERATION IS OPERATED UPON THE EMPLOYEES TABLE WITH A JOB_ID SPECIFIED AS SA_REP AND COMMISSION_PCT WITH SOME VALUE THEN THE TRIGGER RESTRICT_SALARY WILL FIRE CAUSING A INSERTION OF ZERO IN COMMISION_PCT IN THE TABLE. (PLEASE NOTE LINE NO 7).OTHER WISE IF THE JOB IS OTHER THAN SA_REP THEN ROW IS FULLY INSERTED AS DESIRED.

IF AN UPDATE OPERATION IS OPERATED UPON THE TABLE THERE ARE TWO CASES TO BE NOTICED.

1) IF THE OLD VALUE OF COMMISSION_PCT IS A NULL THEN WHILE UPDATION OF SALARY RESTRICT_SALARY WILL FIRE AND THE COMMISSION_PCT WILL BE ASSIGNED A VALUE OF ZERO.(PLEASE SEE LINE NO 9)

2) IF THE OLD VALUE OF COMMISSION_PCT IS NOT NULL THEN RAISE_SALARY WILL FIRE AND NEW VALUE WILL BE WHAT EVER VALUE THAT HAS BEEN SPECIFIED IN THE ACTION.(PLEASE SEE LINE NO 11)INSTEAD OF TRIGGERS

IF THE MODIFICATION IS REQUIERD TO BE DONE ON THE DATA OWNED BY AN UNUPDATEABLE VIEW I.E (A VIEW CONTAINING THE SET OPERATORS, DISTINCT CLAUSE, GROUP FUNCTIONS, OR JOINS BECOMES AN UNUPDATEABLE VIEW) THEN THE INSTEAD OF TRIGGERS ARE USED WHICH ARE FIRED BY THE ORACLE SERVER WITHOUT EXECUTING THE TRIGGERING STATEMENT OPERATING THE DML UPON THE UNDERLYING TABLES SPECIFIED.

CREATE OR REPLACE TRIGGERINSTEAD OFORORON VIEW_NAMEFOR EACH ROW

IF THE VIEW IS UPDATEABLE AND CONTAINS THE INSTEAD OF TRIGGERS THEN THESE TRIGGERS TAKE PRECEDENCE.ALSO THE CHECK OPTIONS ARE NOT TAKEN CARE OF AT THE TIME OF FIRING OF INSTEAD OF TRIGGERS.RATHER IF WANTED THEY MUST BE SPECIFIED IN THE BODY OF INSTEAD OF TRIGGER.

SEE FOR MORE DETAILS ORACLE HAND BOOK

MANAGING TRIGGERS

WE CAN ALTER THE STATUS OF A TRIGGER BY DISABLING OR ENABLING IT.ALTER TRIGGERDISABLE/ENABLEFOR IN CASE OF TABLEALTER TABLEDISABLE/ENABLE ALL TRIGGERSFOR RECOMPILING THE TRIGGER BODYALTER TRIGGERCOMPILEDROPPING A TRIGGERDROP TRIGGER TRIGGER_NAME

CREATING DATABASE TRIGGERS

FOR CREATING A DATABASE TRIGGER FIRST THE TRIGGER CMPONENTS ARE TO BE DECIDED.

A TRIGGER DEFINED FOR A SYSTEM EVENT CAN BE AT A LEVEL OF DATABASE OR SCHEMA.FOR EXAMPLE THE LOG OFF TRIGGERS OR TRIGGERS INVOLVING DDL STATEMENTS ARE AT A LEVEL OF EITHER SCHEMA OR DATABASE. THE DATABASE SHUTDOWN TRIGGERS ARE AT A LEVEL OF SCHEMA.

TRIGGERS DEFINED AT SCHEMA LEVEL FIRES WHENEVER THE TRIGGERING EVENT INVOLVES THE SCHEMA OR TABLE.WHEREAS THE DATABASE LEVEL TRIGGERS FIRE FOR ALL USERS.

FOR DLL TRIGGERS THE POSSIBLE EVENTS MAY BE

1) CREATE STATEMENT2) ALTER STATEMENT]3) OR A DROP STATEMENT

ANY WAY THE CREATE TRIGGER SYNTAX WILL BE REMAINING THE SAME ALL THE TIME.FOR A TRIGGER INVOLVED IN THE SYSYTEM EVENTS LIKE

1) AFTER SERVERERROR2) AFTER LOGON3) BEFORE LOGOFF4) AFTER STARTUP5) BEFORE SHUTDOWN

MUTATING TABLE

IT CAN BE DEFINED AS A TABLE BEING MODIFIED BY AN UPDATE, DELETE INSERT STATEMENT OR THE TABLE IS REQUIRED TO BE UPDATE BY THE EFFECTS OF ON DELETE CASCADE REFERENTIAL INTEGRITY ACTION.

A TRIGGERED TABLE IS ALSO A MUTATING ONE AS WELL AS ANY TABLE REFERENCING IT BY FOREIGN KEY CONSTRAINT.

PROTECTING DATA INTEGRITY WITH TRIGGERS

CREATE OR REPLACE CHECK_SALARYBEFORE UPDATE OF SALARY ON EMPLOYEESFOR EACH ROWWHEN (NEW.SALARY)