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Most Important SQL Queries


Most Important SQL Queries

Important SQL Queries :
---------------------------

Table Name : Employee
EMPLOYEE_ID
FIRST_NAME
LAST_NAME
SALARY
JOINING_DATE
DEPARTMENT
1
Jhon
Abraham
1000000
01-JAN-13 12.00.00 AM
Banking
2
Michael
Clarke
800000
01-JAN-13 12.00.00 AM
Insurance
3
Roy
Thomas
700000
01-FEB-13 12.00.00 AM
Banking
4
Tom
Jose
600000
01-FEB-13 12.00.00 AM
Insurance
5
Jerry
Pinto
650000
01-FEB-13 12.00.00 AM
Insurance
6
Philip
Mathew
750000
01-JAN-13 12.00.00 AM
Services
7
TestName1
123
650000
01-JAN-13 12.00.00 AM
Services
8
TestName2
Lname%
600000
01-FEB-13 12.00.00 AM
Insurance

Table Name : Incentives

EMPLOYEE_REF_ID
INCENTIVE_DATE
INCENTIVE_AMOUNT
1
01-FEB-13
5000
2
01-FEB-13
3000
3
01-FEB-13
4000
1
01-JAN-13
4500
2
01-JAN-13
3500

Database SQL Queries Interview Questions and answers on "SQL Select"


Database SQL Queries Interview Questions and answers on "SQL Select"

1. Get all employee details from the employee table

 Select * from employee 

2. Get First_Name,Last_Name from employee table

 Select first_name, Last_Name from employee 

3. Get First_Name from employee table using alias name “Employee Name”

 Select first_name Employee Name from employee 

4. Get First_Name from employee table in upper case

 Select upper(FIRST_NAME) from EMPLOYEE 

5. Get First_Name from employee table in lower case

Select lower(FIRST_NAME) from EMPLOYEE

6. Get unique DEPARTMENT from employee table

select distinct DEPARTMENT from EMPLOYEE

7. Select first 3 characters of FIRST_NAME from EMPLOYEE

Oracle Equivalent of SQL Server SUBSTRING is SUBSTR, Query : select substr(FIRST_NAME,0,3) from employee

SQL Server Equivalent of Oracle SUBSTR is SUBSTRING, Query : select substring(FIRST_NAME,0,3) from employee

MySQL Server Equivalent of Oracle SUBSTR is SUBSTRING. In MySQL start position is 1, Query : select substring(FIRST_NAME,1,3) from employee


8. Get position of 'o' in name 'Jhon' from employee table

Oracle Equivalent of SQL Server CHARINDEX is INSTR, Query : Select instr(FIRST_NAME,'o') from employee where first_name = 'Jhon'

SQL Server Equivalent of Oracle INSTR is CHARINDEX,Query: Select CHARINDEX('o',FIRST_NAME,0) from employee where first_name = 'Jhon'

MySQL Server Equivalent of Oracle INSTR is LOCATE, Query: Select LOCATE('o',FIRST_NAME) from employee where first_name = 'Jhon'


9. Get FIRST_NAME from employee table after removing white spaces from right side

select RTRIM(FIRST_NAME) from employee


10. Get FIRST_NAME from employee table after removing white spaces from left side

select LTRIM(FIRST_NAME) from employee


11. Get length of FIRST_NAME from employee table

Oracle,MYSQL Equivalent of SQL Server Len is Length , Query :select length(FIRST_NAME) from employee

SQL Server Equivalent of Oracle,MYSQL Length is Len, Query :select len(FIRST_NAME) from employee


12. Get First_Name from employee table after replacing 'o' with '$'

select REPLACE(FIRST_NAME,'o','$') from employee


13. Get First_Name and Last_Name as single column from employee table separated by a '_'

Oracle Equivalent of MySQL concat is '||', Query : Select FIRST_NAME|| '_' ||LAST_NAME from EMPLOYEE

SQL Server Equivalent of MySQL concat is '+', Query : Select FIRST_NAME + '_' +LAST_NAME from EMPLOYEE

MySQL Equivalent of Oracle '||' is concat, Query : Select concat(FIRST_NAME,'_',LAST_NAME) from EMPLOYEE


14. Get FIRST_NAME ,Joining year,Joining Month and Joining Date from employee table

SQL Queries in Oracle
Select FIRST_NAME, 
to_char(joining_date,'YYYY') JoinYear , to_char(joining_date,'Mon'), to_char(joining_date,'dd') from EMPLOYEE
SQL Queries in SQL Server, select SUBSTRING (convert(varchar,joining_date,103),7,4) , SUBSTRING (convert(varchar,joining_date,100),1,3) , SUBSTRING (convert(varchar,joining_date,100),5,2) from EMPLOYEE

SQL Queries in MySQL
select year(joining_date),month(joining_date), DAY(joining_date) from EMPLOYEE



Database SQL Queries Interview Questions and answers on "SQL Order By"

15. Get all employee details from the employee table order by First_Name Ascending

Select * from employee order by FIRST_NAME asc


16. Get all employee details from the employee table order by First_Name descending

Select * from employee order by FIRST_NAME desc


17. Get all employee details from the employee table order by First_Name Ascending and Salary descending

Select * from employee order by FIRST_NAME asc,SALARY desc


Database SQL Queries Interview Questions and answers on "SQL Where Condition"

18. Get employee details from employee table whose employee name is “Jhon”

Select * from EMPLOYEE where FIRST_NAME = 'Jhon'


19. Get employee details from employee table whose employee name are “Jhon” and “Roy”

Select * from EMPLOYEE where FIRST_NAME in ('Jhon','Roy')


20. Get employee details from employee table whose employee name are not “Jhon” and “Roy”

Select * from EMPLOYEE where FIRST_NAME not in ('Jhon','Roy')


Database SQL Queries Interview Questions and answers on "SQL Wild Card"

21. Get employee details from employee table whose first name starts with 'J'

Select * from EMPLOYEE where FIRST_NAME like 'J%'


22. Get employee details from employee table whose first name contains 'o'

Select * from EMPLOYEE where FIRST_NAME like '%o%'


23. Get employee details from employee table whose first name ends with 'n'

Select * from EMPLOYEE where FIRST_NAME like '%n'


Database SQL Queries Interview Questions and answers on "SQL Pattern Matching"

24. Get employee details from employee table whose first name ends with 'n' and name contains 4 letters

Select * from EMPLOYEE where FIRST_NAME like '___n' (Underscores)


25. Get employee details from employee table whose first name starts with 'J' and name contains 4 letters

Select * from EMPLOYEE where FIRST_NAME like 'J___' (Underscores)


26. Get employee details from employee table whose Salary greater than 600000

Select * from EMPLOYEE where Salary > 600000


27. Get employee details from employee table whose Salary less than 800000

Select * from EMPLOYEE where Salary < 800000


28. Get employee details from employee table whose Salary between 500000 and 800000

Select * from EMPLOYEE where Salary between 500000 and 800000


29. Get employee details from employee table whose name is 'Jhon' and 'Michael'

Select * from EMPLOYEE where FIRST_NAME in ('Jhon','Michael')



Database SQL Queries Interview Questions and answers on "SQL DATE Functions"

30. Get employee details from employee table whose joining year is “2013”

SQL Queries in Oracle, 
Select * from EMPLOYEE where to_char(joining_date,'YYYY') = '2013'

SQL Queries in SQL Server,
Select * from EMPLOYEE where SUBSTRING(convert(varchar,joining_date,103),7,4) = '2013'

SQL Queries in MySQL,
 Select * from EMPLOYEE where year(joining_date) = '2013'


31. Get employee details from employee table whose joining month is “January”

SQL Queries in Oracle
Select * from EMPLOYEE where to_char(joining_date,'MM') = '01' or Select * from EMPLOYEE where to_char(joining_date,'Mon') = 'Jan'

SQL Queries in SQL Server,
 Select * from EMPLOYEE where SUBSTRING(convert(varchar,joining_date,100),1,3) = 'Jan'

SQL Queries in MySQL, Select * from EMPLOYEE where month(joining_date) = '01'


32. Get employee details from employee table who joined before January 1st 2013

SQL Queries in Oracle, 
Select * from EMPLOYEE where JOINING_DATE < to_date('01/01/2013','dd/mm/yyyy')

SQL Queries in SQL Server (Format - “MM/DD/YYYY”)
Select * from EMPLOYEE where joining_date < '01/01/2013'

SQL Queries in MySQL (Format - “YYYY-DD-MM”),
Select * from EMPLOYEE where joining_date < '2013-01-01'


33. Get employee details from employee table who joined after January 31st

SQL Queries in Oracle, 
Select * from EMPLOYEE where JOINING_DATE > to_date('31/01/2013','dd/mm/yyyy')

SQL Queries in SQL Server and MySQL (Format - “MM/DD/YYYY”), Select * from EMPLOYEE where joining_date >'01/31/2013'

SQL Queries in MySQL (Format - “YYYY-DD-MM”), 
Select * from EMPLOYEE where joining_date > '2013-01-31'

34. Get employee details from employee table who joined between January 1st and January 31st

SQL Queries in Oracle, 
Select * from EMPLOYEE where JOINING_DATE between to_date('01/01/2013','dd/mm/yyyy') and to_date('31/01/2013','dd/mm/yyyy')

SQL Queries in SQL Server (Format - “MM/DD/YYYY”), 
Select * from EMPLOYEE where joining_date between '01/01/2013' and '01/31/2013'

SQL Queries in MySQL (Format - “YYYY-DD-MM”),
 Select * from EMPLOYEE where joining_date between '2013-01-01' and '2013-01-31'


35. Get Joining Date and Time from employee table

SQL Queries in Oracle, 
select to_char(JOINING_DATE,'dd/mm/yyyy hh:mi:ss') from EMPLOYEE

SQL Queries in SQL Server, 
Select convert(varchar(19),joining_date,121) from EMPLOYEE

SQL Queries in MySQL
Select CONVERT(DATE_FORMAT(joining_date,'%Y-%m-%d-%H:%i:00'),DATETIME) from EMPLOYEE


36. Get Joining Date,Time including milliseconds from employee table

SQL Queries in Oracle, 
select to_char(JOINING_DATE,'dd/mm/yyyy HH:mi:ss.ff') from EMPLOYEE . Column Data Type should be “TimeStamp”

SQL Queries in SQL Server,
 select convert(varchar,joining_date,121) from EMPLOYEE

SQL Queries in MySQL, 
Select MICROSECOND(joining_date) from EMPLOYEE



37. Get difference between JOINING_DATE and INCENTIVE_DATE from employee and incentives table

Select FIRST_NAME,INCENTIVE_DATE - JOINING_DATE from employee a inner join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

38. Get database date

SQL Queries in Oracle, 
select sysdate from dual

SQL Queries in SQL Server, 
select getdate()

SQL Query in MySQL
select now()



Database SQL Queries Interview Questions and answers on "SQL Escape Characters"




39. Get names of employees from employee table who has '%' in Last_Name. Tip : Escape character for special characters in a query.

SQL Queries in Oracle,
Select FIRST_NAME from employee where Last_Name like '%?%%'

SQL Queries in SQL Server,
Select FIRST_NAME from employee where Last_Name like '%[%]%'

SQL Queries in MySQL,Select FIRST_NAME from employee where Last_Name like '%\%%'


40. Get Last Name from employee table after replacing special character with white space
SQL Queries in Oracle,
 Select translate(LAST_NAME,'%',' ') from employee

SQL Queries in SQL Server adn MySQL,
 Select REPLACE(LAST_NAME,'%',' ') from employee



Database SQL Queries Interview Questions and answers on "SQL Group By Functions"



41. Get department,total salary with respect to a department from employee table.

Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by department


42. Get department,total salary with respect to a department from employee table order by total salary descending

Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by DEPARTMENT order by Total_Salary descending




Database SQL Queries Interview Questions and answers on "SQL Mathematical Operations and Group By"





43. Get department,no of employees in a department,total salary with respect to a department from employee table order by total salary descending


Select DEPARTMENT,count(FIRST_NAME),sum(SALARY) Total_Salary from employee group by DEPARTMENT order by Total_Salary descending



44. Get department wise average salary from employee table order by salary ascending


select DEPARTMENT,avg(SALARY) AvgSalary from employee group by DEPARTMENT order by AvgSalary asc



45. Get department wise maximum salary from employee table order by salary ascending


select DEPARTMENT,max(SALARY) MaxSalary from employee group by DEPARTMENT order by MaxSalary asc


46. Get department wise minimum salary from employee table order by salary ascending


select DEPARTMENT,min(SALARY) MinSalary from employee group by DEPARTMENT order by MinSalary asc


47. Select no of employees joined with respect to year and month from employee table

SQL Queries in Oracle, 
select to_char (JOINING_DATE,'YYYY') Join_Year,to_char (JOINING_DATE,'MM') Join_Month,count(*) Total_Emp from employee group by to_char (JOINING_DATE,'YYYY'),to_char(JOINING_DATE,'MM')

SQL Queries in SQL Server, 
select datepart (YYYY,JOINING_DATE) Join_Year,datepart (MM,JOINING_DATE) Join_Month,count(*) Total_Emp from employee group by datepart(YYYY,JOINING_DATE), datepart(MM,JOINING_DATE)

SQL Queries in MySQL
select year (JOINING_DATE) Join_Year,month (JOINING_DATE) Join_Month,count(*) Total_Emp from employee group by year(JOINING_DATE), month(JOINING_DATE)



48. Select department,total salary with respect to a department from employee table where total salary greater than 800000 order by Total_Salary descinding

Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by DEPARTMENT having sum(SALARY) > 800000 order by Total_Salary desc



Database SQL Queries Interview Questions and answers on "SQL Inner Join"




49. Select first_name, incentive amount from employee and incentives table for those employees who have incentives

Select FIRST_NAME,INCENTIVE_AMOUNT from employee a inner join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID


50. Select first_name, incentive amount from employee and incentives table for those employees who have incentives a
d incentive amount greater than 3000

Select FIRST_NAME,INCENTIVE_AMOUNT from employee a inner join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID and INCENTIVE_AMOUNT > 3000


51. Select first_name, incentive amount from employee and incentives table for all employess even if they didn't get incentives

Select FIRST_NAME,INCENTIVE_AMOUNT from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID


52. Select first_name, incentive amount from employee and incentives table for all employees even if they didn't get incentives and set incentive amount as 0 for those employees who didn't get incentives.

SQL Queries in Oracle
Select FIRST_NAME,nvl(INCENTIVE_AMOUNT,0) from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in SQL Server,
Select FIRST_NAME, 
ISNULL(INCENTIVE_AMOUNT,0) from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in MySQL
Select FIRST_NAME, IFNULL(INCENTIVE_AMOUNT,0) from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID


53. Select first_name, incentive amount from employee and incentives table for all employees who got incentives using left join


SQL Queries in Oracle,
 Select FIRST_NAME,nvl(INCENTIVE_AMOUNT,0) from employee a right join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID


SQL Queries in SQL Server,
 Select FIRST_NAME, isnull(INCENTIVE_AMOUNT,0) from employee a right join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in MySQL, Select FIRST_NAME, IFNULL(INCENTIVE_AMOUNT,0) from employee a right join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID


54. Select max incentive with respect to employee from employee and incentives table using sub query

SQL Queries in Oracle,
select DEPARTMENT,(select nvl(max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE

SQL Queries in SQL Server,
select DEPARTMENT,(select ISNULL(max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE

SQL Queries in SQL Server, 
select DEPARTMENT,(selectIFNULL (max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE



Database SQL Queries Interview Questions and answers on "Top N Salary"

55. Select TOP 2 salary from employee table

SQL Queries in Oracle, 
select * from (select * from employee order by SALARY desc) where rownum < 3

SQL Queries in SQL Server, 
select top 2 * from employee order by salary desc

SQL Queries in MySQL, 
select * from employee order by salary desc limit 2


56. Select TOP N salary from employee table

SQL Queries in Oracle
, select * from (select * from employee order by SALARY desc) where rownum < N + 1

SQL Queries in SQL Server, 
select top N * from employee

SQL Queries in MySQL,
select * from employee order by salary desc limit N

57. Select 2nd Highest salary from employee table

SQL Queries in Oracle, 
select min(salary) from (select * from (select * from employee order by SALARY desc) where rownum < 3)

SQL Queries in SQL Server, 
select min(SALARY) from (select top 2 * from employee) a

SQL Queries in MySQL,
select min(SALARY) from (select * from employee order by salary desc limit 2) a


58. Select Nth Highest salary from employee table

SQL Queries in Oracle,
select min(salary) from (select * from (select * from employee order by SALARY desc) where rownum < N + 1)

SQL Queries in SQL Server
, select min(SALARY) from (select top N * from employee) a

SQL Queries in MySQL,
select min(SALARY) from (select * from employee order by salary desc limit N) a



Database SQL Queries Interview Questions and answers on "SQL Union"



59. Select First_Name,LAST_NAME from employee table as separate rows

select FIRST_NAME from EMPLOYEE union select LAST_NAME from EMPLOYEE


60. Select employee details from employee table if data exists in incentive table


select * from EMPLOYEE where exists (select * from INCENTIVES)



61. Select 20 % of salary from Jhon , 10% of Salary for roy and for other 15 % of salary from employee table


SELECT FIRST_NAME, CASE FIRST_NAME WHEN 'Jhon' THEN SALARY * .2 WHEN 'Roy' THEN SALARY * .10 ELSE SALARY * .15 END "Deduced_Amount" FROM EMPLOYEE

62. Select Banking as 'Bank Dept', Insurance as 'Insurance Dept' and Services as 'Services Dept' from employee table


SQL Queries in Oracle, 
SELECT distinct DECODE (DEPARTMENT, 'Banking', 'Bank Dept', 'Insurance', 'Insurance Dept', 'Services', 'Services Dept') FROM EMPLOYEE


SQL Queries in SQL Server and MySQL, 
SELECT case DEPARTMENT when 'Banking' then 'Bank Dept' when 'Insurance' then 'Insurance Dept' when 'Services' then 'Services Dept' end FROM EMPLOYEE


63. Delete employee data from employee table who got incentives in incentive table

delete from EMPLOYEE where EMPLOYEE_ID in (select EMPLOYEE_REF_ID from INCENTIVES)


64. Insert into employee table Last Name with ''' (Single Quote - Special Character, Use single quote before special character )

Insert into employee (LAST_NAME) values ('Test''')


65. Select Last Name from employee table which contain only numbers

Select * from EMPLOYEE where lower(LAST_NAME) = upper(LAST_NAME)



Database SQL Queries Interview Questions and answers on "SQL Table Scripts"




66. Write create table syntax for employee table
Oracle -

CREATE TABLE EMPLOYEE (
EMPLOYEE_ID NUMBER,
FIRST_NAME VARCHAR2(20 BYTE),
LAST_NAME VARCHAR2(20 BYTE),
SALARY FLOAT(126),
JOINING_DATE TIMESTAMP (6) DEFAULT sysdate,
DEPARTMENT VARCHAR2(30 BYTE) )


SQL Server -
CREATE TABLE EMPLOYEE(
EMPLOYEE_ID int NOT NULL,
FIRST_NAME varchar(50) NULL,
LAST_NAME varchar(50) NULL,
SALARY decimal(18, 0) NULL,
JOINING_DATE datetime2(7) default getdate(),
DEPARTMENT varchar(50) NULL)


67. Write syntax to delete table employee

DROP table employee;


68. Write syntax to set EMPLOYEE_ID as primary key in employee table

ALTER TABLE EMPLOYEE add CONSTRAINT EMPLOYEE_PK PRIMARY KEY(EMPLOYEE_ID)


69. Write syntax to set 2 fields(EMPLOYEE_ID,FIRST_NAME) as primary key in employee table

ALTER TABLE EMPLOYEE add CONSTRAINT EMPLOYEE_PK PRIMARY KEY(EMPLOYEE_ID,FIRST_NAME)


70. Write syntax to drop primary key on employee table

Alter TABLE EMPLOYEE drop CONSTRAINT EMPLOYEE_PK;


71. Write Sql Syntax to create EMPLOYEE_REF_ID in INCENTIVES table as foreign key with respect to EMPLOYEE_ID in employee table

ALTER TABLE INCENTIVES ADD CONSTRAINT INCENTIVES_FK FOREIGN KEY (EMPLOYEE_REF_ID) REFERENCES EMPLOYEE(EMPLOYEE_ID)


72. Write SQL to drop foreign key on employee table

ALTER TABLE INCENTIVES drop CONSTRAINT INCENTIVES_FK;


73. Write SQL to create Orcale Sequence

CREATE SEQUENCE EMPLOYEE_ID_SEQ
START WITH 0 NOMAXVALUE MINVALUE 0 NOCYCLE NOCACHE NOORDER;


74. Write Sql syntax to create Oracle Trigge before insert of each row in employee table

CREATE OR REPLACE TRIGGER EMPLOYEE_ROW_ID_TRIGGER
BEFORE INSERT ON EMPLOYEE FOR EACH ROW
DECLARE
seq_no number(12);
BEGIN
select EMPLOYEE_ID_SEQ.nextval into seq_no from dual ;
:new EMPLOYEE_ID := seq_no;
END;
SHOW ERRORS;


75. Oracle Procedure


76. Oracle View


77. Oracle materialized view



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