HCL Technologies Oracle SQL Queries In Written Test

HCL Technologies Frequently Asked Oracle SQL Queries In Written Test Interview Questions

How to add column in a table

Syntax:

ALTER TABLE table_name
  ADD column_name column-definition;
Example:

Consider that already existing table customers. Now, add a new column customer_age into the table customers.

ALTER TABLE customers
  ADD customer_age varchar2(50);
Now, a new column "customer_age" will be added in customers table.

How to add multiple columns in the existing table

Syntax:

ALTER TABLE table_name
  ADD (column_1 column-definition,
       column_2 column-definition,
       ...
       column_n column_definition);
Example

ALTER TABLE customers
  ADD (customer_type varchar2(50),
       customer_address varchar2(50));
Now, two columns customer_type and customer_address will be added in the table customers.

HCL Technologies Frequently Asked Oracle SQL Queries In Written Test Interview Questions

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.

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')
);