Download Sql queries notes for placement and more Cheat Sheet Database Management Systems (DBMS) in PDF only on Docsity!
SQL Queries Interview Questions and Answers on "SQL
Select" - Examples
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 'John' from employee table
Oracle Equivalent of SQL Server CHARINDEX is INSTR , Query : Select instr(FIRST_NAME,'o') from employee where first_name = 'John'
SQL Server Equivalent of Oracle INSTR is CHARINDEX , Query: Select CHARINDEX('o',FIRST_NAME,0) from employee where first_name = 'John'
MySQL Server Equivalent of Oracle INSTR is LOCATE , Query: Select LOCATE('o',FIRST_NAME) from employee where first_name = 'John'
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
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 'John' and 'Michael'
Select * from EMPLOYEE where FIRST_NAME in ('John','Michael')
SQL Queries Interview Questions and Answers on "SQL
DATE Functions" - Examples
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) =
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'
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()
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 descending
Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by DEPARTMENT having sum(SALARY) > 800000 order by Total_Salary desc
SQL Queries Interview Questions and Answers on "SQL
Joins" - Examples
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 and 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
employes 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,(select IFNULL (max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE
Advanced SQL Queries Interview Questions and
Answers on "Top N Salary" - Examples
55. Select TOP 2 salary from employee table
type of both the columns are VARCHAR, union is made possible. Difference between UNION and UNION ALL is that , UNION query return only distinct values.
"Advanced SQL Queries Interview Questions and
Answers"
61. Select employee details from employee table if data exists in incentive table?
select * from EMPLOYEE where exists (select * from INCENTIVES)
Explanation : Here exists statement helps us to do the job of If statement. Main
query will get executed if the sub query returns at least one row. So we can
consider the sub query as "If condition" and the main query as "code block" inside
the If condition. We can use any SQL commands (Joins, Group By , having etc) in
sub query. This command will be useful in queries which need to detect an event
and do some activity.
62. How to fetch data that are common in two query results?
select * from EMPLOYEE where EMPLOYEE_ID INTERSECT select * from EMPLOYEE where EMPLOYEE_ID < 4
Explanation : Here INTERSECT command is used to fetch data that are common in 2 queries. In this example, we had taken EMPLOYEE table in both the queries.We can apply INTERSECT command on different tables. The result of the above query will return employee details of "ROY" because, employee id of ROY is 3, and both query results have the information about ROY.
63. Get Employee ID's of those employees who didn't receive incentives without using
sub query?
select EMPLOYEE_ID from EMPLOYEE
MINUS
select EMPLOYEE_REF_ID from INCENTIVES
Explanation : To filter out certain information we use MINUS command. What MINUS Command odes is that, it returns all the results from the first query, that are not part of the second query. In our example, first three employees received the incentives. So query will return employee id's 4 to
64. Select 20 % of salary from John , 10% of Salary for Roy and for other 15 % of
salary from employee table
SELECT FIRST_NAME, CASE FIRST_NAME WHEN 'John' THEN SALARY * .2 WHEN 'Roy' THEN SALARY * .10 ELSE SALARY * .15 END "Deduced_Amount" FROM EMPLOYEE
Explanation : Here we are using SQL CASE statement to achieve the desired results. After case statement, we had to specify the column on which filtering is applied. In our case it is "FIRST_NAME". And in then condition, specify the name of filter like John, Roy etc. To handle conditions outside our filter, use else block where every one other than John and Roy enters.
65. 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
Explanation : Here DECODE keyword is used to specify the alias name. In oracle we had specify, Column Name followed by Actual Name and Alias Name as arguments. In SQL Server and MySQL, we can use the earlier switch case statements for alias names.
66. 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)
Explanation : Trick about this question is that we can't delete data from a table based on some condition in another table by joining them. Here to delete multiple entries from EMPLOYEE table, we need to use Subquery. Entries will get deleted based on the result of Subquery.
67. Insert into employee table Last Name with " ' " (Single Quote - Special Character)
Tip - Use another single quote before special character
Insert into employee (LAST_NAME) values ('Test''')
68. Select Last Name from employee table which contain only numbers
Select * from EMPLOYEE where lower(LAST_NAME) = upper(LAST_NAME)
Explanation : Here in order to achieve the desired result, we use ASCII property of the database. If we get results for a column using Lower and Upper commands, ASCII of both results will be same for numbers. If there is any alphabets in the column, results will differ.
69. Write a query to rank employees based on their incentives for a month
select FIRST_NAME,INCENTIVE_AMOUNT,DENSE_RANK() OVER (PARTITION BY INCENTIVE_DATE ORDER BY INCENTIVE_AMOUNT DESC) AS Rank from EMPLOYEE a, INCENTIVES b where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID
DEPARTMENT varchar(50) NULL)
72. Write syntax to delete table employee
DROP table employee;
73. Write syntax to set EMPLOYEE_ID as primary key in employee table
ALTER TABLE EMPLOYEE add CONSTRAINT EMPLOYEE_PK PRIMARY KEY(EMPLOYEE_ID)
74. 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)
75. Write syntax to drop primary key on employee table
Alter TABLE EMPLOYEE drop CONSTRAINT EMPLOYEE_PK;
76. 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)
77. Write SQL to drop foreign key on employee table
ALTER TABLE INCENTIVES drop CONSTRAINT INCENTIVES_FK;
78. Write SQL to create Orcale Sequence
CREATE SEQUENCE EMPLOYEE_ID_SEQ START WITH 0 NOMAXVALUE MINVALUE 0 NOCYCLE
NOCACHE NOORDER;
79. Write Sql syntax to create Oracle Trigger 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;
80. Oracle Procedure 81. Oracle View
An example oracle view script is given below
create view Employee_Incentive as select FIRST_NAME,max(INCENTIVE_AMOUNT) INCENTIVE_AMOUNT from EMPLOYEE a, INCENTIVES b where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID group by FIRST_NAME
82. Oracle materialized view - Daily Auto Refresh
CREATE MATERIALIZED VIEW Employee_Incentive
REFRESH COMPLETE
START WITH SYSDATE
NEXT SYSDATE + 1 AS
select FIRST_NAME,INCENTIVE_DATE,INCENTIVE_AMOUNT from EMPLOYEE a, INCENTIVES b
where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID
83. Oracle materialized view - Fast Refresh on Commit
Create materialized view log for fast refresh. Following materialized view script wont get executed if materialized view log doesn't exists
CREATE MATERIALIZED VIEW MAT_Employee_Incentive_Refresh
BUILD IMMEDIATE
REFRESH FAST ON COMMIT AS
select FIRST_NAME,max(INCENTIVE_AMOUNT) from EMPLOYEE a, INCENTIVES b
where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID group by FIRST_NAME
84. What is SQL Injection?
SQL Injection is one of the the techniques uses by hackers to hack a website by injecting SQL commands in data fields.
