SQL Queries Interview Questions
CREATE TABLE PRODUCTS
(
PRODUCT_ID INTEGER,
PRODUCT_NAME VARCHAR2(30)
);
CREATE TABLE SALES
(
SALE_ID INTEGER,
PRODUCT_ID INTEGER,
YEAR INTEGER,
Quantity INTEGER,
PRICE INTEGER
);
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 SALES VALUES ( 1, 100, 2010, 25, 5000);
INSERT INTO SALES VALUES ( 2, 100, 2011, 16, 5000);
INSERT INTO SALES VALUES ( 3, 100, 2012, 8, 5000);
INSERT INTO SALES VALUES ( 4, 200, 2010, 10, 9000);
INSERT INTO SALES VALUES ( 5, 200, 2011, 15, 9000);
INSERT INTO SALES VALUES ( 6, 200, 2012, 20, 9000);
INSERT INTO SALES VALUES ( 7, 300, 2010, 20, 7000);
INSERT INTO SALES VALUES ( 8, 300, 2011, 18, 7000);
INSERT INTO SALES VALUES ( 9, 300, 2012, 20, 7000);
COMMIT;
The products table contains the below data.
SELECT * FROM PRODUCTS;
PRODUCT_ID PRODUCT_NAME
-----------------------
100 Nokia
200 IPhone
300 Samsung
The sales table contains the following data.
SELECT * FROM SALES;
SALE_ID PRODUCT_ID YEAR QUANTITY PRICE
--------------------------------------
1 100 2010 25 5000
2 100 2011 16 5000
3 100 2012 8 5000
4 200 2010 10 9000
5 200 2011 15 9000
6 200 2012 20 9000
7 300 2010 20 7000
8 300 2011 18 7000
9 300 2012 20 7000
Here Quantity is the number of products sold in each year. Price is the sale price of each product.
I hope you have created the tables in your oracle database. Now try to solve the below SQL queries.
1. Write a SQL query to find the products which have continuous increase in sales every year?
Solution:
Here “Iphone” is the only product whose sales are increasing every year.
STEP1: First we will get the previous year sales for each product. The SQL query to do this is
SELECT P.PRODUCT_NAME,
S.YEAR,
S.QUANTITY,
LEAD(S.QUANTITY,1,0) OVER (
PARTITION BY P.PRODUCT_ID
ORDER BY S.YEAR DESC
) QUAN_PREV_YEAR
FROM PRODUCTS P,
SALES S
WHERE P.PRODUCT_ID = S.PRODUCT_ID;
PRODUCT_NAME YEAR QUANTITY QUAN_PREV_YEAR
-----------------------------------------
Nokia 2012 8 16
Nokia 2011 16 25
Nokia 2010 25 0
IPhone 2012 20 15
IPhone 2011 15 10
IPhone 2010 10 0
Samsung 2012 20 18
Samsung 2011 18 20
Samsung 2010 20 0
Here the lead analytic function will get the quantity of a product in its previous year.
STEP2: We will find the difference between the quantities of a product with its previous year’s quantity. If this difference is greater than or equal to zero for all the rows, then the product is a constantly increasing in sales. The final query to get the required result is
SELECT PRODUCT_NAME
FROM
(
SELECT P.PRODUCT_NAME,
S.QUANTITY -
LEAD(S.QUANTITY,1,0) OVER (
PARTITION BY P.PRODUCT_ID
ORDER BY S.YEAR DESC
) QUAN_DIFF
FROM PRODUCTS P,
SALES S
WHERE P.PRODUCT_ID = S.PRODUCT_ID
)A
GROUP BY PRODUCT_NAME
HAVING MIN(QUAN_DIFF) >= 0;
PRODUCT_NAME
------------
IPhone
2. Write a SQL query to find the products which does not have sales at all?
Solution:
“LG” is the only product which does not have sales at all. This can be achieved in three ways.
Method1:
Using the NOT EXISTS operator.
SELECT P.PRODUCT_NAME
FROM PRODUCTS P
WHERE NOT EXISTS
(SELECT 1 FROM SALES S WHERE S.PRODUCT_ID = P.PRODUCT_ID);
PRODUCT_NAME
------------
LG
Method2: Using the NOT IN operator.
SELECT P.PRODUCT_NAME
FROM PRODUCTS P
WHERE P.PRODUCT_ID NOT IN
(SELECT DISTINCT PRODUCT_ID FROM SALES);
PRODUCT_NAME
------------
LG
Method3:
Using left outer join.
SELECT P.PRODUCT_NAME
FROM PRODUCTS P
LEFT OUTER JOIN
SALES S
ON (P.PRODUCT_ID = S.PRODUCT_ID);
WHERE S.QUANTITY IS NULL
PRODUCT_NAME
------------
LG
3. Write a query to select the top product sold in each year?
Solution:
Nokia is the top product sold in the year 2010. Similarly, Samsung in 2011 and IPhone, Samsung in 2012. The query for this is
SELECT PRODUCT_NAME,
YEAR
FROM
(
SELECT P.PRODUCT_NAME,
S.YEAR,
RANK() OVER (
PARTITION BY S.YEAR
ORDER BY S.QUANTITY DESC
) RNK
FROM PRODUCTS P,
SALES S
WHERE P.PRODUCT_ID = S.PRODUCT_ID
) A
WHERE RNK = 1;
PRODUCT_NAME YEAR
--------------------
Nokia 2010
Samsung 2011
IPhone 2012
Samsung 2012
4. Write a SQL query to find the products whose sales decreased in 2012 compared to 2011?
Solution:
Here Nokia is the only product whose sales decreased in year 2012 when compared with the sales in the year 2011. The SQL query to get the required output is
SELECT P.PRODUCT_NAME
FROM PRODUCTS P,
SALES S_2012,
SALES S_2011
WHERE P.PRODUCT_ID = S_2012.PRODUCT_ID
AND S_2012.YEAR = 2012
AND S_2011.YEAR = 2011
AND S_2012.PRODUCT_ID = S_2011.PRODUCT_ID
AND S_2012.QUANTITY < S_2011.QUANTITY;
PRODUCT_NAME
------------
Nokia
5. Write a query to find the total sales of each product.?
Solution:
This is a simple query. You just need to group by the data on PRODUCT_NAME and then find the sum of sales.
SELECT P.PRODUCT_NAME,
NVL( SUM( S.QUANTITY*S.PRICE ), 0) TOTAL_SALES
FROM PRODUCTS P
LEFT OUTER JOIN
SALES S
ON (P.PRODUCT_ID = S.PRODUCT_ID)
GROUP BY P.PRODUCT_NAME;
PRODUCT_NAME TOTAL_SALES
---------------------------
LG 0
IPhone 405000
Samsung 406000
Nokia 245000
6. 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
);
PRODUCT_NAME YEAR QUANTITY
--------------------------
Nokia 2010 25
IPhone 2012 20
Samsung 2012 20
Samsung 2010 20
7. 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
8. 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);
PRODUCT_NAME YEAR RATIO
-----------------------------
IPhone 2011 0.333333333
IPhone 2012 0.444444444
IPhone 2010 0.222222222
Nokia 2012 0.163265306
Nokia 2011 0.326530612
Nokia 2010 0.510204082
Samsung 2010 0.344827586
Samsung 2012 0.344827586
Samsung 2011 0.310344828
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