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Oracle - The self documenting dictionary Oracle's Data dictionary is itself self documenting. we can query DICTIONARY AND DICT_COLUMNS views for descriptions of the data dictionary views and their columns. The following query gives the descriptions of all of the data dictionary views. SELECT table_name, comments FROM dictionary ORDER BY table_name; It gives the large amount of output. By using where class we can focus a smaller set of views as like the following query. SELECT table_name, comments FROM dictionary WHERE table_name LIKE '%TABLE%' ORDER BY table_name It returns all views containing the word 'TABLE' Like wise We can query the DICT_COLUMNS view also. It gives the descriptions for the columns for all views. Following query retrieves descriptions for the columns in ALL_TAB_COLUMNS. SELECT column_name, comments FROM dict_columns WHERE table_name = 'ALL_TAB_COLUMNS'; This is a sample one. We can learn lot about oracle through data d

Which SELECT statement will the result 'elloworld' from the string 'HelloWorld'? A. SELECT SUBSTR( 'HelloWorld',1) FROM dual; B. SELECT INITCAP(TRIM ('HelloWorld', 1,1)) FROM dual; C. SELECT LOWER(SUBSTR('HellowWorld', 1, 1) FROM dual; D. SELECT LOWER(SUBSTR('HelloWorld', 2, 1) FROM dual; E. SELECT LOWER(TRIM ('H' FROM 'HelloWorld')) FROM dual; Answer: E Explanation: TRIM function accept a string describing the data you would like to trim from a column value. It can trim from both side of column value i.e. left and right. In the following statement this functionwill trim as SELECT LOWER(TRIM ('+' FROM 'HelloWorld')) FROM dual; From the above statement trim function will remove the character 'H' from 'HelloWorld' and LOWER function will convert the remaining character to lower case.

Processes Oracle uses many small (focused) processes to manage and control the Oracle instance. This allows for optimum execution on multi-processor systems using multi-core and multi-threaded technology. Some of these processes include: PMON - Process Monitor SMON - System Monitor ARCn - Redo Log Archiver LGWR - Redo Log Writer DBWn - Database Writer CKPT - Checkpoint process RECO - Recoverer CJQn - Job Queue Coordinator QMNn - Queue-monitor processes Dnnn - Dispatcher Processes (multiplex server-processes on behalf of users) Snnn - Shared server processes (serve client-requests) MMAN - Internal process (used for internal database tasks) LSP0 - Logical standby coordinator process (controls Data Guard log-application) MRP - Media-recovery process (detached recovery-server process) MMON - Memory-monitor process MMNL - Memory monitor light (gathers and stores AWR statistics) PSP0 - Process-spawner (spawns Oracle processes) RFS - Remote file server process (archive to a remote site) DBRM

Examine the structure of the EMPLOYEES table: EMPLOYEE_ID NUMBER NOT NULL EMP_NAME VARCHAR2(30) JOB_ID VARCHAR2(20) SAL NUMBER MGR_ID NUMBER DEPARTMENT_ID NUMBER You want to create a SQL script file that contains an INSERT statement. When the script is run, the INSERT statement should insert a row with the specified values into the EMPLOYEES table. The INSERT statement should pass values to the table columns as specified below: EMPLOYEE_ID: Next value from the sequence EMP_ID_SEQEMP_NAME and JOB_ID: As specified by the user during run time, through substitution variables SAL: 2000 MGR_ID: No value DEPARTMENT_ID: Supplied by the user during run time throughsubstitutionvariable. The INSERT statement should fail if the user supplies a value other than20 or 50. Which INSERT statement meets the above requirements? A. INSERT INTO employees VALUES (emp_id_seq.NEXTVAL, '&ename', '&jobid', 2000, NULL,&did); B. INSERT INTO employees VALUES (emp_id_seq.NEXTVAL, '&a

We can get the nth maximum value through query by using the combination of order by clause and rownum pseudo column. The Query following. SELECT MIN(columnname) FROM ( SELECT coumnname FROM tablename ORDER BY columnname DESC) WHERE rownum <= n

Can we insert more than 1 row with 1 qyery in same table/diff tables? Yes, we insert more than 1 row with 1 qyery by using the following method? syntax INSERT ALL INTO tablename1 (fieldlist) VALUES (valuelist) INTO tablename2 (fieldlist) VALUES (valuelist) INTO tablename3 (fieldlist) VALUES (valuelist) SELECT * FROM DUAL; Example: insert all into student (sno, name) values (1, 'Raja') into student (sno, name) values (2 'Ravi') into student (sno, name) values (3, 'Balu') select * from dual; We can use more than 1 table also. insert all into student (sno, name) values (1, 'Raja') into student (sno, name) values (2 'Ravi') into emp (eno, name) values (1, 'Mani') select * from dual; Interview quesitions and answers, objective type questions with answers : http://atchaya.com/ora/orahome.html Oracle forum : http://atchaya.wikidot.com/forum/c-91091/discussion-about-oracle

Write a PL/SQL Program for the following output --*-- -***- ***** -***- --*-- Answer The output based on the value of 'n' declare n number(2) default 20; i number(2); j number(2); h number(2); s number(2); b varchar2(1) default 'I'; begin s := 1; if n mod 2 = 0 then n := n+1; end if; h := n/2 -1; for i in 1..n loop for j in 1..h loop dbms_output.put('-'); end loop; for j in 1..s loop dbms_output.put('*'); end loop; for j in 1..h loop dbms_output.put('-'); end loop; dbms_output.put_line(' '); if n = s then b := 'D'; end if; IF b='I' then s := s+2; h := h-1; else s := s-2; h := h+1; end if; end loop; end;

Evaluate the SQL statement DROP TABLE DEPT Which four statements are true of the SQL statement? A. You cannot roll back this statement. B. All pending transactions are committed. C. Al views based on the DEPT table are deleted. D. All indexes based on the DEPT table are dropped. E. All data in the table is deleted, and the table structure is also deleted. F.All data in the table is deleted, but the structure of the table is retained. G.All synonyms based on the DEPT table are deleted. Answer: A, B, D and E Explanation: A. You cannot roll back DROP TABLE statement. B. All pending transactions related on this table arecommitted. D. If the table is dropped, Oracle automatically drops any index, trigger and constraintassociated with the table as well. E. All data in the table is deleted, and the table structure is also deleted. Incorrect Answers C: All views based on the DEPT table become invalid, but they are not deleted. F: All data in the table is deleted, and the table structure is als

I have updated some tables and before commit if I will give one DDL command means what will happen? For example CREATE TABLE test(fldname number(10)); insert into test (fldname) values (10); insert into test (fldname) values (20); After that without giving Commit statement, I issued one DDL command CREATE TABLE test1( sno number(10)) What aobut the previous inserts? Is it committed or not? explain. Answer: I checked this and found the following 3 points. Point No. 1: If we give a DDL command with syntax error means it will not commit and gives the error. For example the following statement CREATE TABLE test(fldname number(10), ); note that the comma, gives "invalid identifier.. " error and without committing the INSERT statements. Point No. 2: If the given DDL command executes without any error means it will auto commit the INSERT statements. Point No. 3: If we give a DDL command without any syntax error and that statement not execute also auto commit the INSERT st

You are running a pl/sql block or procedure called parent In that procedure you called another one procedure namely child and that procedure contains commit statement. After calling the child procedure the transactions done in parent procedure are also committed due to the child procedure commit statement. But you want to rollback or commit the parent procedure whole transactions based on your requirement after the calling procedure child. In this situation, you should add the "pragma autonomus transaction" in child procedure. If you add this statement then it acts as a separate. If you use commit in child procedure it will not affect the parent procedure. Example : CREATE OR REPLACE PROCEDURE parent() AS BEGIN UPDATE tab1 SET fieldname = value WHERE condition; UPDATE tab2 SET fieldname = value WHERE condition; child(); UPDATE tab4 SET fieldname = value WHERE condition; IF parentcondition COMMIT; ELSE ROLLBACK; END IF; END. CREATE OR REPLACE PROCEDURE child() AS PRAGMA AUTONO

Suppose Database D1 contains 100 tables.. How 2 select the tables which are modified at 10am today? 1. SELECT table_name, table_owner FROM all_tab_modifications WHERE to_char(timestamp,'YYYYMMDDHH24MM') = to_char(sysdate,'YYYYMMDD')'1000' This will gives the table names which are modified (insert, update, delete, truncated) at 10 AM. 2. SELECT scn_to_timestamp(max(ora_rowscn)) FROM ;

How many number of rows, I can insert into a table simultaenously? Answer : Method 1: If you want to insert multiple rows with a single INSERT statement, you can use a subquery instead of the VALUES clause. Rows returned from the subquery will be inserted the target table. Example: INSERT INTO tablename1 SELECT fieldnamelist FROM tablename WHERE condition

The EMP table contains these columns: LAST NAME VARCHAR2(25) SALARY NUMBER(6,2) DEPARTMENT_ID NUMBER(6) You need to display the employees who have not been assigned to any department. You write the SELECT statement: SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMP WHERE DEPARTMENT_ID = NULL; What is true about this SQL statement? A. The SQL statement displays the desired results. B. The column in the WHERE clause should be changed to display the desired results. C. The operator in the WHERE clause should be changed to display the desired results. D. The WHERE clause should be changed to use an outer join to display the desired results. Answer: C Explanation: The operator in the WHERE clause should be changed to display the desired results. There are times when you want to substitute a value in place of NULL. Oracle provides this functionality with a special function, called NVL(). You can use operation equal with the keywords IS NULL, or you can achieve desired results using NVL() fu

Examine the description of the STUDENTS table: STD_ID NUMBER(4) COURSE_ID VARCHARD2(10) START_DATE DATE END_DATE DATE Which two aggregate functions are valid on the START_DATE column? (Choose two) A. SUM(start_date) B. AVG(start_date) C. COUNT(start_date) D. AVG(start_date, end_date) E. MIN(start_date) F. MAXIMUM(start_date) Answer: C & E Explanation: It is possible to apply COUNT() and MIN() functions on the column with DATE data type. Incorrect Answers A: Function SUM() cannot be used with DATE data type column. B: Function AVG() cannot be used with DATE data type column. D: Function AVG() cannot be used with DATE data type column, and function AVG() just has one parameter X, not two. It averages all X column values returned by the SELECT statement. F: There is no MAXIMUM() function in Oracle, only MAX() function exists.

Examine the description of the EMPLOYEES table: EMP_ID NUMBER(4) NOT NULL LAST_NAME VARCHAR2(30) NOT NULL FIRST_NAME VARCHAR2(30) DEPT_ID NUMBER(2) JOB_CAT VARCHARD2(30) SALARY NUMBER(8,2) Which statement shows the maximum salary paid in each job category of each department? A.SELECT dept_id, job_cat, MAX(salary) FROM employees WHERE salary > MAX(salary); B.SELECT dept_id, job_cat, MAX(salary) FROM employees GROUP BY dept_id, job_cat; C. SELECT dept_id, job_cat, MAX(salary) FROM employees; D. SELECT dept_id, job_cat, MAX(salary) FROM employees GROUP BY dept_id; Answer: B Explanation: This answer provides correct syntax and semantics to show the maximum salary paid in each job category of each department. Incorrect Answers A: This query will not return any row because condition SALARY > MAX(SALARY) is FALSE. C: This query will return error because you cannot show maximum salary with DEPT_ID and JOB_CAT without grouping by these columns. D: The GROUP BY clause is missing JOB_ID col

You are sorting data in a table in you SELECT statement in descending order. The column you are sorting on contains NULL records, where will the NULL record appears? A.At the beginning of the list. B.At the end of the list. C.In the middle of the list. D.At the same location they are listed in the unordered table. Answer: A Explanation: When sorting a column with null values in ascending order then the oracle places the Null values at the end of the list if the sorting is in descending order the oracle places the null values at the start of the list.

Which two statements are true about WHERE and HAVING clauses? (Choose two) A. A WHERE clause can be used to restrict both rows and groups. B. A WHERE clause can be used to restrict rows only. C. A HAVING clause can be used to restrict both rows and groups. D. A HAVING clause can be used to restrict groups only. Answer: B, C Explanation : HAVING clause to specify which groups are to be displayed and thus further restrict the groups on the basis of aggregate information. The Oracle server performs the following steps when youuse the Having clause 1. rows are grouped 2. the group function is applied to the group 3. the group that match the criteria in the Having clause are displayed. WHERE clause cannot be use to restrict groups HAVING clause use to restrict groups WHERE clause cannot be use when there is group functions. Incorrect Answers : A. Where clause cannot be use to restrict groups D. When HAVING clause is use rows are grouped as well.

The ORDERS table has these columns: ORDER_ID NUMBER(4) NOT NULL CUSTOMER_ID NUMBER(12) NOT NULL ORDER_TOTAL NUMBER(10,2) The ORDERS table tracks the Order number, the order total, and the customer to whom the Order belongs. Which two statements retrieve orders with an inclusive total that ranges between 100.00 and 2000.00 dollars? A.SELECT customer_id, order_id, order_total FROM orders RANGE ON order_total (100 AND 2000) INCLUSIVE; B.SELECT customer_id, order_id, order_total FROM orders HAVING order_total BETWEEN 100 and 2000; C. SELECT customer_id, order_id, order_total FROM orders WHERE order_total BETWEEN 100 and 2000; D. SELECT customer_id, order_id, order_total FROM orders WHERE order_total >= 100 and <= 2000; Answer:C Explanation: Answers C provides correct results to show. You can use BETWEEN or comparison operations to retrieve data. Incorrect Answers A: There is no RANGE ON or INCLUSIVE keyword in Oracle. B: HAVING clause can be use only in conjunction with the GROUP BY

The ORDERS table has these columns: ORDER_ID NUMBER(4) NOT NULL CUSTOMER_ID NUMBER(12) NOT NULL ORDER_TOTAL NUMBER(10,2) The ORDERS table tracks the Order number, the order total, and the customer to whom the Order belongs. Which two statements retrieve orders with an inclusive total that ranges between 100.00 and 2000.00 dollars? A.SELECT customer_id, order_id, order_total FROM orders RANGE ON order_total (100 AND 2000) INCLUSIVE; B.SELECT customer_id, order_id, order_total FROM orders HAVING order_total BETWEEN 100 and 2000; C. SELECT customer_id, order_id, order_total FROM orders WHERE order_total BETWEEN 100 and 2000; D. SELECT customer_id, order_id, order_total FROM orders WHERE order_total >= 100 and <= 2000; Answer:C Explanation: Answers C provides correct results to show. You can use BETWEEN or comparison operations to retrieve data. Incorrect Answers A: There is no RANGE ON or INCLUSIVE keyword in Oracle. B: H

The STUDENT_GRADES table has these columns: STUDENT_ID NUMBER(12) SEMESTER_END DATE GPA NUMBER(4,3) The registrar has requested a report listing the students grade point averages (GPA), sorted from highest grade point average to lowest within each semester, starting from the earliest date. Which statement accomplishes this? A.SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end DESC, gpa DESC; B.SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end ASC, gpa ASC; C. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY semester_end, gpa DESC; D. SELECT student_id, semester_end, gpa FROM student_grades ORDER BY gpa DESC, semester_end DESC; Answer :C Explanation: This answer shows correct syntax and semantics to receive desired result. Incorrect Answers A: Semesters will be sorted started from the oldest date, not the earliest. B: GPA data will be sorted in ascending order, what is opposite to our task. D: Semester

Question: 2. You want to display the titles of books that meet these criteria: 1. Purchased before January 21, 20012. Price is less then $500 or greater than $900 You want to sort the results by their data of purchase, starting with the most recently boughtbook. Which statement should you use? A. SELECT book_title FROM books WHERE price between 500 and 900 AND purchase_date < '21-JAN-2001' ORDER BY purchase_date; B. SELECT book_titleFROM books WHERE price IN (500,900) AND purchase_date < '21-JAN-2001' ORDER BY purchase date ASC; C. SELECT book_titleFROM books WHERE price <> 900 AND purchase_date < '21-JAN-2001' ORDER BY purchase date DESC; D. SELECT book_titleFROM books WHERE (price <> 900) AND purchase_date < '21-JAN-2001' ORDER BY purchase date DESC; Answer: D Explanation: This statement provides required results. Incorrect Answers: A: This query will show books with price in range $500 and $900, not less then $500 or greater

Question 1. You need to display the last names of those employees who have the letter "A" as the second character in their names. Which SQL statement displays the required results? A. SELECT last_nameFROM EMPWHERE last_name LIKE '_A%'; B. SELECT last_nameFROM EMPWHERE last name ='*A%' C. SELECT last_nameFROM EMPWHERE last name ='_A%'; D. SELECT last_nameFROM EMPWHERE last name LIKE '*A%' Answer: A Explanation: Statement in this answer will show correct results because usage of operator LIKE and format mask '_A%' extract the last names of those employees who have the letter 'A' as the second character in their names. Symbol '_' in format mask substitute exactly one symbol and cannot be NULL. Incorrect Answers B: This statement will return only names starting from symbol '*'. It cannot be used as substitution symbol. C: Usage of equity operator here is not appropriate in this case: query will look exact for fi