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DBMS Interview Questions and Answers

Ques 11. Have you heard about sixth normal form?

Ans.

If we want relational system in conjunction with time we use sixth normal form. At this moment
SQL Server does not supports it directly.

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Ques 12. What are DML and DDL statements?
Ans.
DML stands for Data Manipulation Statements. They update data values in table. Below are the most important DDL statements:- 
=>SELECT - gets data from a database table 
=> UPDATE - updates data in a table 
=> DELETE - deletes data from a database table 
=> INSERT INTO - inserts new data into a database table
DDL stands for Data definition Language. They change structure of the database objects like table, index etc. Most important DDL statements are as shown below:- 
=>CREATE TABLE - creates a new table in the database. 
=>ALTER TABLE – changes table structure in database. 
=>DROP TABLE - deletes a table from database 
=> CREATE INDEX - creates an index 
=> DROP INDEX - deletes an index
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Ques 13. How do we select distinct values from a table?
Ans.
DISTINCT keyword is used to return only distinct values. Below is syntax:- Column age and
Table wbEmp
SELECT DISTINCT age FROM wbEmp
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Ques 14. What is Like operator for and what are wild cards in DMBS?
Ans.
LIKE operator is used to match patterns. A "%" sign is used to define the pattern.
Below SQL statement will return all words with letter "S"
SELECT * FROM pcdsEmployee WHERE EmpName LIKE 'S%'
Below SQL statement will return all words which end with letter "S"
SELECT * FROM pcdsEmployee WHERE EmpName LIKE '%S'
Below SQL statement will return all words having letter "S" in between
SELECT * FROM pcdsEmployee WHERE EmpName LIKE '%S%'
"_" operator (we can read as “Underscore Operator”). “_” operator is the character defined at that point. In the below sample fired a query Select name from pcdsEmployee where name like
'_s%' So all name where second letter is “s” is returned.
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Ques 15. Can you explain Insert, Update and Delete query in DBMS?
Ans.
Insert statement is used to insert new rows in to table. Update to update existing data in the
table. Delete statement to delete a record from the table. Below code snippet for Insert, Update and Delete :-
INSERT INTO wbEmployee SET name='maxwell',age='22';
UPDATE wbEmployee SET age='22' where name='maxwell';
DELETE FROM wbEmployee WHERE name = 'david';
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