Oracle SQL Queries Frequently Asked In Hitachi Written Test

Oracle SQL Queries Most Frequently Asked In Hitachi Written Test Interview

How to modify column of a table

Syntax:

ALTER TABLE table_name
  MODIFY column_name column_type;
Example:

ALTER TABLE customers
  MODIFY customer_name varchar2(100) not null;
Now the column column_name in the customers table is modified
to varchar2 (100) and forced the column to not allow null values.

How to modify multiple columns of a table
Syntax:

ALTER TABLE table_name
  MODIFY (column_1 column_type,
          column_2 column_type,
          ...
          column_n column_type);
Example:

ALTER TABLE customers
  MODIFY (customer_name varchar2(100) not null,
          city varchar2(100));
This will modify both the customer_name and city columns in the table.

How to drop column of a table

Syntax:

ALTER TABLE table_name
  DROP COLUMN column_name;
Example:

ALTER TABLE customers

  DROP COLUMN customer_name;
This will drop the customer_name column from the table.

How to rename column of a table

Syntax:

ALTER TABLE table_name
  RENAME COLUMN old_name to new_name;
Example:

ALTER TABLE customers
 RENAME COLUMN customer_name to cname;
This will rename the column customer_name into cname.

How to rename table

Syntax:

ALTER TABLE table_name
  RENAME TO new_table_name;
Example:

ALTER TABLE customers
RENAME TO retailers;
This will rename the customer table into "retailers" table.

Oracle SQL Queries Most Frequently Asked In Hitachi Written Test Interview

Write a query to find the products whose quantity sold in a year should be greater than the average quantity of the product sold across all the years?

Solution:

This can be solved with the help of correlated query. The SQL query for this is

SELECT P.PRODUCT_NAME,
       S.YEAR,
       S.QUANTITY
FROM   PRODUCTS P,
       SALES S
WHERE  P.PRODUCT_ID = S.PRODUCT_ID
AND    S.QUANTITY >
       (SELECT AVG(QUANTITY)
       FROM SALES S1
       WHERE S1.PRODUCT_ID = S.PRODUCT_ID
       );

Write a query to compare the products sales of "IPhone" and "Samsung" in each year? The output should look like as

YEAR IPHONE_QUANT SAM_QUANT IPHONE_PRICE SAM_PRICE
---------------------------------------------------
2010   10           20       9000         7000
2011   15           18       9000         7000
2012   20           20       9000         7000

Solution:

By using self-join SQL query we can get the required result. The required SQL query is

SELECT S_I.YEAR,
       S_I.QUANTITY IPHONE_QUANT,
       S_S.QUANTITY SAM_QUANT,
       S_I.PRICE    IPHONE_PRICE,
       S_S.PRICE    SAM_PRICE
FROM   PRODUCTS P_I,
       SALES S_I,
       PRODUCTS P_S,
       SALES S_S
WHERE  P_I.PRODUCT_ID = S_I.PRODUCT_ID
AND    P_S.PRODUCT_ID = S_S.PRODUCT_ID
AND    P_I.PRODUCT_NAME = 'IPhone'
AND    P_S.PRODUCT_NAME = 'Samsung'
AND    S_I.YEAR = S_S.YEAR

Write a query to find the ratios of the sales of a product?

Solution:

The ratio of a product is calculated as the total sales price in a particular year divide by the total sales price across all years. Oracle provides RATIO_TO_REPORT analytical function for finding the ratios. The SQL query is

SELECT P.PRODUCT_NAME,
       S.YEAR,
       RATIO_TO_REPORT(S.QUANTITY*S.PRICE)
         OVER(PARTITION BY P.PRODUCT_NAME ) SALES_RATIO
FROM   PRODUCTS P,
       SALES S
WHERE (P.PRODUCT_ID = S.PRODUCT_ID);

In the SALES table quantity of each product is stored in rows for every year. Now write a query to transpose the quantity for each product and display it in columns? The output should look like as

PRODUCT_NAME QUAN_2010 QUAN_2011 QUAN_2012
------------------------------------------
IPhone       10        15        20
Samsung      20        18        20
Nokia        25        16        8

Solution:

Oracle 11g provides a pivot function to transpose the row data into column data. The SQL query for this is

SELECT * FROM
(
SELECT P.PRODUCT_NAME,
       S.QUANTITY,
       S.YEAR
FROM   PRODUCTS P,
       SALES S
WHERE (P.PRODUCT_ID = S.PRODUCT_ID)
)A
PIVOT ( MAX(QUANTITY) AS QUAN FOR (YEAR) IN (2010,2011,2012));

If you are not running oracle 11g database, then use the below query for transposing the row data into column data.

SELECT P.PRODUCT_NAME,
       MAX(DECODE(S.YEAR,2010, S.QUANTITY)) QUAN_2010,
       MAX(DECODE(S.YEAR,2011, S.QUANTITY)) QUAN_2011,
       MAX(DECODE(S.YEAR,2012, S.QUANTITY)) QUAN_2012
FROM   PRODUCTS P,
       SALES S
WHERE (P.PRODUCT_ID = S.PRODUCT_ID)
GROUP BY P.PRODUCT_NAME;

Write a query to find the number of products sold in each year?

Solution:

To get this result we have to group by on year and the find the count. The SQL query for this question is

SELECT YEAR,
       COUNT(1) NUM_PRODUCTS
FROM   SALES
GROUP BY YEAR;

Write a query to generate sequence numbers from 1 to the specified number N?

Solution:

SELECT LEVEL FROM DUAL CONNECT BY LEVEL<=&N;

Write a query to display only Sunday dates from Jan, 2000 to till now?

Solution:

SELECT  C_DATE,
        TO_CHAR(C_DATE,'DY')
FROM
(
  SELECT TO_DATE('01-JAN-2000','DD-MON-YYYY')+LEVEL-1 C_DATE
  FROM   DUAL
  CONNECT BY LEVEL <=
       (SYSDATE - TO_DATE('01-JAN-2000','DD-MON-YYYY')+1)
)
WHERE TO_CHAR(C_DATE,'DY') = 'SUN';

Write a query to duplicate each row based on the value in the repeat column? The input table data looks like as below

Products, Repeat
----------------
A,         3
B,         5
C,         2

Now in the output data, the product A should be repeated 3 times, B should be repeated 5 times and C should be repeated 2 times. The output will look like as below

Products, Repeat
----------------
A,        3
A,        3
A,        3
B,        5
B,        5
B,        5
B,        5
B,        5
C,        2
C,        2

Solution:

SELECT PRODUCTS,
       REPEAT
FROM   T,
      ( SELECT LEVEL L FROM DUAL
        CONNECT BY LEVEL <= (SELECT MAX(REPEAT) FROM T)
      ) A
WHERE T.REPEAT >= A.L
ORDER BY T.PRODUCTS;

Write a query to display each letter of the word "BIG" in a separate row?

B
I
G

Solution:

SELECT SUBSTR('SMILE',LEVEL,1) A
FROM   DUAL
CONNECT BY LEVEL <=LENGTH('BIG');

Convert the string "SMILE" to Ascii values?  The output should look like as 83,77,73,76,69. Where 83 is the ascii value of S and so on.

The ASCII function will give ascii value for only one character. If you pass a string to the ascii function, it will give the ascii value of first letter in the string. Here i am providing two solutions to get the ascii values of string.

Solution 1:

SELECT SUBSTR(DUMP('SMILE'),15)
FROM DUAL;

Solution2:

SELECT WM_CONCAT(A)
FROM
(
SELECT ASCII(SUBSTR('SMILE',LEVEL,1)) A
FROM   DUAL
CONNECT BY LEVEL <=LENGTH('SMILE')
);

Consider the following friends table as the source

Name, Friend_Name

-----------------

sam,   ram

sam,   vamsi

vamsi, ram

vamsi, jhon

ram,   vijay

ram,   anand

Here ram and vamsi are friends of sam; ram and jhon are friends of vamsi and so on. Now write a query to find friends of friends of sam. For sam; ram,jhon,vijay and anand are friends of friends. The output should look as

Name, Friend_of_Firend

----------------------

sam,    ram

sam,    jhon

sam,    vijay

sam,    anand

Solution:

SELECT  f1.name,

        f2.friend_name as friend_of_friend

FROM    friends f1,

        friends f2

WHERE   f1.name = 'sam'

AND     f1.friend_name = f2.name;

In the output, you can see ram is displayed as friends of friends. This is because, ram is mutual friend of sam and vamsi. Now extend the above query to exclude mutual friends. The output should look as

Name, Friend_of_Friend

----------------------

sam,    jhon

sam,    vijay

sam,    anand

Solution:

SELECT  f1.name,

        f2.friend_name as friend_of_friend

FROM    friends f1,

        friends f2

WHERE   f1.name = 'sam'

AND     f1.friend_name = f2.name

AND     NOT EXISTS 

        (SELECT 1 FROM friends f3 

         WHERE f3.name = f1.name 

         AND   f3.friend_name = f2.friend_name);

Write a query to get the top 5 products based on the quantity sold without using the row_number analytical function? The source data looks as

Products, quantity_sold, year

-----------------------------

A,         200,          2009

B,         155,          2009

C,         455,          2009

D,         620,          2009

E,         135,          2009

F,         390,          2009

G,         999,          2010

H,         810,          2010

I,         910,          2010

J,         109,          2010

L,         260,          2010

M,         580,          2010

Solution:

SELECT  products,

        quantity_sold,

        year

FROM

(

  SELECT  products,

          quantity_sold, 

          year,

          rownum r

  from    t

  ORDER BY quantity_sold DESC

)A

WHERE r <= 5;

Write a query to produce the same output using row_number analytical function?

Solution:

SELECT  products,

        quantity_sold,

        year

FROM

(

  SELECT products,

         quantity_sold,

         year,

         row_number() OVER(

            ORDER BY quantity_sold DESC) r

  from   t

)A

WHERE r <= 5;

write a query to get the top 5 products in each year based on the quantity sold?

Solution:

SELECT  products,

        quantity_sold,

        year

FROM

(

   SELECT products,

          quantity_sold,

          year,

          row_number() OVER(

               PARTITION BY year 

               ORDER BY quantity_sold DESC) r

   from   t

)A

WHERE r <= 5;

Load the below products table into the target table.

CREATE TABLE PRODUCTS

(

       PRODUCT_ID     INTEGER,

       PRODUCT_NAME   VARCHAR2(30)

);

INSERT INTO PRODUCTS VALUES ( 100, 'Nokia');

INSERT INTO PRODUCTS VALUES ( 200, 'IPhone');

INSERT INTO PRODUCTS VALUES ( 300, 'Samsung');

INSERT INTO PRODUCTS VALUES ( 400, 'LG');

INSERT INTO PRODUCTS VALUES ( 500, 'BlackBerry');

INSERT INTO PRODUCTS VALUES ( 600, 'Motorola');

COMMIT;

SELECT * FROM PRODUCTS;

PRODUCT_ID PRODUCT_NAME

-----------------------

100        Nokia

200        IPhone

300        Samsung

400        LG

500        BlackBerry

600        Motorola

The requirements for loading the target table are:

Select only 2 products randomly.

Do not select the products which are already loaded in the target table with in the last 30 days.

Target table should always contain the products loaded in 30 days. It should not contain the products which are loaded prior to 30 days.

Solution:

First we will create a target table. The target table will have an additional column INSERT_DATE to know when a product is loaded into the target table. The target 

table structure is

CREATE TABLE TGT_PRODUCTS

(

       PRODUCT_ID     INTEGER,

       PRODUCT_NAME   VARCHAR2(30),

       INSERT_DATE    DATE

);

The next step is to pick 5 products randomly and then load into target table. While selecting check whether the products are there in the 

INSERT INTO TGT_PRODUCTS

SELECT  PRODUCT_ID,

        PRODUCT_NAME,

        SYSDATE INSERT_DATE

FROM

(

SELECT  PRODUCT_ID,

 PRODUCT_NAME

FROM PRODUCTS S

WHERE   NOT EXISTS (

           SELECT 1

           FROM   TGT_PRODUCTS T

           WHERE  T.PRODUCT_ID = S.PRODUCT_ID

        )

ORDER BY DBMS_RANDOM.VALUE --Random number generator in oracle.

)A

WHERE ROWNUM <= 2;

The last step is to delete the products from the table which are loaded 30 days back. 

DELETE FROM TGT_PRODUCTS

WHERE  INSERT_DATE < SYSDATE - 30;

Load the below CONTENTS table into the target table. 

CREATE TABLE CONTENTS

(

  CONTENT_ID  INTEGER,

  CONTENT_TYPE VARCHAR2(30)

);

INSERT INTO CONTENTS VALUES (1,'MOVIE');

INSERT INTO CONTENTS VALUES (2,'MOVIE');

INSERT INTO CONTENTS VALUES (3,'AUDIO');

INSERT INTO CONTENTS VALUES (4,'AUDIO');

INSERT INTO CONTENTS VALUES (5,'MAGAZINE');

INSERT INTO CONTENTS VALUES (6,'MAGAZINE');

COMMIT;

SELECT * FROM CONTENTS;

CONTENT_ID CONTENT_TYPE

-----------------------

1          MOVIE

2          MOVIE

3          AUDIO

4          AUDIO

5          MAGAZINE

6          MAGAZINE

The requirements to load the target table are: 

Load only one content type at a time into the target table.

The target table should always contain only one contain type.

The loading of content types should follow round-robin style. First MOVIE, second AUDIO, Third MAGAZINE and again fourth Movie.

Solution: 

First we will create a lookup table where we mention the priorities for the content types. The lookup table “Create Statement” and data is shown below. 

CREATE TABLE CONTENTS_LKP

(

  CONTENT_TYPE VARCHAR2(30),

  PRIORITY     INTEGER,

  LOAD_FLAG  INTEGER

);

INSERT INTO CONTENTS_LKP VALUES('MOVIE',1,1);

INSERT INTO CONTENTS_LKP VALUES('AUDIO',2,0);

INSERT INTO CONTENTS_LKP VALUES('MAGAZINE',3,0);

COMMIT;

SELECT * FROM CONTENTS_LKP;

CONTENT_TYPE PRIORITY LOAD_FLAG

---------------------------------

MOVIE         1          1

AUDIO         2          0

MAGAZINE      3          0

Here if LOAD_FLAG is 1, then it indicates which content type needs to be loaded into the target table. Only one content type will have LOAD_FLAG as 1. The other content types will have LOAD_FLAG as 0. The target table structure is same as the source table structure. 

The second step is to truncate the target table before loading the data 

TRUNCATE TABLE TGT_CONTENTS;

The third step is to choose the appropriate content type from the lookup table to load the source data into the target table. 

INSERT INTO TGT_CONTENTS

SELECT  CONTENT_ID,

 CONTENT_TYPE 

FROM CONTENTS

WHERE CONTENT_TYPE = (SELECT CONTENT_TYPE FROM CONTENTS_LKP WHERE LOAD_FLAG=1);

The last step is to update the LOAD_FLAG of the Lookup table. 

UPDATE CONTENTS_LKP

SET LOAD_FLAG = 0

WHERE LOAD_FLAG = 1;

UPDATE CONTENTS_LKP

SET LOAD_FLAG = 1

WHERE PRIORITY = (

SELECT DECODE( PRIORITY,(SELECT MAX(PRIORITY) FROM CONTENTS_LKP) ,1 , PRIORITY+1)

FROM   CONTENTS_LKP

WHERE  CONTENT_TYPE = (SELECT DISTINCT CONTENT_TYPE FROM TGT_CONTENTS)

);