Oracle SQL Queries Asked In Apple Written Test Interview

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)

);

Oracle SQL Queries Most Frequently Asked In Apple Written Test Interview

How to retrieve 2nd highest sal in each departement from emp and dept tables using GROUP BY?

SELECT e.DeptNo, MAX(e.Sal),d.DeptName Salary


FROM Emp e left outer join dept d ON e.DeptNo=d.DeptNo


WHERE e.Sal <


(SELECT MAX(Sal)


 FROM Emp


 WHERE DeptNo = e.DeptNo)


GROUP BY e.DeptNo,d.DeptName

Find the 3rd MAX and MIN salary in the emp table?

select distinct sal from emp e1 where 3 = (select count(distinct sal) from emp e2 where e1.sal <= e2.sal);

select distinct sal from emp e1 where 3 = (select count(distinct sal) from emp e2where e1.sal >= e2.sal);

If there are two tables emp1 and emp2, and both have common record. How can I fetch all the records but common records only once?

(Select * from emp) Union (Select * from emp1)

How to fetch only common records from two tables emp and emp1?

(Select * from emp) Intersect (Select * from emp1)

How can I retrive all records of emp1 those should not present in emp2?

(Select * from emp) Minus (Select * from emp1)

Get the first day of the month?

Quickly returns the first day of current month. Instead of current month you want to find first day of month where a date falls, replace SYSDATE with any date column/value.

SELECT TRUNC (SYSDATE, 'MONTH') "First day of current month"
    FROM DUAL;

Get the last day of the month?

This query is similar to above but returns last day of current month. One thing worth noting is that it automatically takes care of leap year. So if you have 29 days in Feb, it will return 29/2. Also similar to above query replace SYSDATE with any other date column/value to find last day of that particular month.

SELECT TRUNC (LAST_DAY (SYSDATE)) "Last day of current month"
    FROM DUAL;

Get the first day of the Year

First day of year is always 1-Jan. This query can be use in stored procedure where you quickly want first day of year for some calculation.

SELECT TRUNC (SYSDATE, 'YEAR') "Year First Day" FROM DUAL;

Get the last day of the year

Similar to above query. Instead of first day this query returns last day of current year.

SELECT ADD_MONTHS (TRUNC (SYSDATE, 'YEAR'), 12) - 1 "Year Last Day" FROM DUAL

Get number of days in current month

Now this is useful. This query returns number of days in current month. You can change SYSDATE with any date/value to know number of days in that month.

SELECT CAST (TO_CHAR (LAST_DAY (SYSDATE), 'dd') AS INT) number_of_days
  FROM DUAL;

Get number of days left in current month

Below query calculates number of days left in current month.

SELECT SYSDATE,
       LAST_DAY (SYSDATE) "Last",
       LAST_DAY (SYSDATE) - SYSDATE "Days left"
  FROM DUAL;

Get number of days between two dates

Use this query to get difference between two dates in number of days.

SELECT ROUND ( (MONTHS_BETWEEN ('01-Feb-2014', '01-Mar-2012') * 30), 0)
          num_of_days
  FROM DUAL;

OR

SELECT TRUNC(sysdate) - TRUNC(e.hire_date) FROM employees;
Use second query if you need to find number of days since some specific date. In this example number of days since any employee is hired.

Display each months start and end date upto last month of the year

This clever query displays start date and end date of each month in current year. You might want to use this for certain types of calculations.

SELECT ADD_MONTHS (TRUNC (SYSDATE, 'MONTH'), i) start_date,
       TRUNC (LAST_DAY (ADD_MONTHS (SYSDATE, i))) end_date
  FROM XMLTABLE (
          'for $i in 0 to xs:int(D) return $i'
          PASSING XMLELEMENT (
                     d,
                     FLOOR (
                        MONTHS_BETWEEN (
                           ADD_MONTHS (TRUNC (SYSDATE, 'YEAR') - 1, 12),
                           SYSDATE)))
          COLUMNS i INTEGER PATH '.');

Get number of seconds passed since today (since 00:00 hr)

SELECT (SYSDATE - TRUNC (SYSDATE)) * 24 * 60 * 60 num_of_sec_since_morning
  FROM DUAL;

Get number of seconds left today (till 23:59:59 hr)

SELECT (TRUNC (SYSDATE+1) - SYSDATE) * 24 * 60 * 60 num_of_sec_left
  FROM DUAL;

Check if a table exists in the current database schema

A simple query that can be used to check if a table exists before you create it. This way you can make your create table script rerunnable. Just replace table_name with actual table you want to check. This query will check if table exists for current user (from where the query is executed).

SELECT table_name
  FROM user_tables
 WHERE table_name = 'TABLE_NAME';