Mysql Revision Tour

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Revision Tour of MySQL

Q1. Define primary key, candidate key, alternate key and foreign key?

Ans.

Primary Key : A set of one or more attributes that can uniquely identify a row in a table. It cant be

repeated and cant be NULL.

eg. admno of student table

Candidate Key : Attribute combinations in a table that can serve as a primary key are known as candidate

key.

eg. admno and roll of student table

Alternate Key : A candidate key other than primary key is called alternate key.

eg. admno of student table is primary key then rollno is alternate ey.

Q2. What is Degree, Cardinality?

Ans.

Degree : Number of columns (or) attributes (or) Fields in a table

Cardinality : Number of Rows (or) types (or) records in a table (Relation)

Q3. Difference between CHAR and VARCHAR?

Ans.

CHAR VARCHAR

1. It specifies fixed length character string it specifies variable lengh character string

2. it adds spaces on right of the string it truncates spaces

Q4. Name ACID properties of transaction?

Ans. Atomicity, Consistency, Isolation, Durabillity

Q5. What is SQL? Name the classification of SQL Statements?

Ans.

SQL (Structured Query Language) is a standard language which is used to manipulate relational

database.

1. DDL (Data Defination Language) eg. create, alter, drop

2. DML (Data Manipulation Language) eg. insert, update, delete

3. TCL (Transaction Control Language ) eg. commit, rollback, savepoint

4. DCL (Data Control Language) Grant, Revoke



Q6. How would you display tables in a database?

Ans.

show tables

Q7. Which sql clause is used to restrict the rows returned by a Query?

Ans.

Distinct clause

Q8. Write MySQL command to display list of existing databases?

Ans.

show databases

Q9. Which command is used to add a new tuple in a table?

Ans.

Insert Into

Q10. Difference between WHERE clause and HAVING clause?

Ans.

Where clause is used to retrieve the records by specifying the condition for each individual row.

whereas Having clause is used to place condition on groups and aggregate functions.

Q11. A table Trains has degree 3 and cardinality 8. What is he number of rows and columns in it?

Ans.

Number of columns (degree) = 3

Number of rows (cardinality) = 8

Q12. Difference between count(*) and count(column)?

Ans.

Count(*) counts the number of characters includeing NULL and Not NULL whereas count(column) counts

the Not NULL values.

Q13. How would you view constraints, viewing columns associated in a Relation (table)?

Ans.

Using DESC (or) Describe command

Q14. Difference between DROP TABLE and DELETE?

DROP TABLE DELETE

1. DROP TABLE is DDL Command Delete is DML command

2. It is used to delete the contents and table

structure

It is used to delete row(s) or contents of table



Q15. What is the purpose of ORDER By Clause?

Ans.

Order By clause is used to sort the query output (i.e. in Ascending Order or Descending Order)

Q16. What are the TCL Commands ?

Ans.

Commit, Rollback and Savepoint.

Q17. How would you begin a new transaction?

Ans.

By using START TRANSACTION

Q18. Write a statemnt to set auto commit to off?

Ans.

SET AUTOCOMMIT = 0;

Q19. How would you delete a column from a table (give syntax)?

Ans. ALTER TABLE tablename DROP columnname

Q20. How would you change the data type of a column?

Ans.

ALTER TABLE tablename MODIFY column datatype(size)

Q21. Which command is used to save the changes permanently in the database?

Ans.

COMMIT

Q22. Which command is used to undo (or) cancel the previous transaction is a database?

Ans.

ROLLBACK

Q23. What is the purpose of SELECT statement ? Give its syntax ?

Ans. To display (or) to list (or) to view the information retrieved from a table (s)

SELECT column1,column2, column... from table1, table2, ... where condition order by column group by

column having condition.

Q24. Write operators used in SQL?

(i) BETWEEN..AND to specify range as a condtion

(ii) IN Operation To specify list of values

(iii) LIKE To specify pattern matching condition using %, _ characters



a. % - specify any and all characters

b. _ - any single character

Q25. Neha created a table later on she realize that there is no need to include CLASS column which

command she should use to do so? [tablename is student]

Ans.

ALTER TABLE student Drop Class

Q26. A table name OFFICE has 6 rows 10 columns and another table name STAFF has 3 rows and 5

columns. How many rows and columns will be there, it we obtain the cartesian product of these two

tables?

Ans.

Number of Rows = 18 (6x3)

Number of Columns (15 (10+5)

Q27. What are six relational operations

Ans.

>, =,



Q33. What is Equi-Join?

Ans.

The Query which combines he rows from multiple table by using equality condition on the common

columns (i.e. Primary Key of one table to Foreign key of another table) is called equi join.

Q34. Which command is used to modify existing data in a table?

Ans.

UPDATE Command

Syntax : UPDATE tablename SET columnname=value WHERE condition.

Q35. Which command is used to delete rows from a table?

Ans.

DELETE command

Syntax. DELETE FROM tablename WHERE condition

Q36. What are Constraints? Give examples?

Ans.

Constriant is a limitation or Specification or condition on a column(s).

e.g. Primary key, Not Null, Check , Foreign Key etc.

Q37. In a database there is a table Cabinet. The data entry operator is not able to insert a null value in a

column. What may the possible reason?

Ans.

The column is defined with NOT NULL or primary key constraint.

Q38. Do the Primary key of a table accept null or duplicate values?

Ans. NO. it does not accept duplicate or null values.

Q39. What is a Transaction?

Ans.

A Logical unit or work that must be done in a logical order and successfully as a grouop or not done at all

is called a transaction.

Q40. What is the purpose of inserting savepoint?

Ans.

The savepoint statement defines a marker in a transaction. It is used to rollback a transaction till the

marker.

Q41. Difference between ROLLBACK and ROLLBACK TO?

Ans. ROLLBACK is used to undo the transaction to the beginning whereas ROLLBACK TO is used to undo

the transaction upto the given savepoint name.



Q42. What is the difference between IN and BETWEEN operator?

Ans.

Between operator is used to check for numeric range comparison whereas IN operator is used for batch

comparison.

Q43. What are the types of ROLLBACK?

Ans.

Rollback can be of two types

1. Complete Rollback - it will undo the transaction to its starting point

2. Partial Rollback - it will undo the transaction to the specified savepoint.

Q44. How to check the current setting of autocommit in MySQL?

Ans.

To check the current setting of autocommit we have to issue the following command

select @@autocommit;

Q45. Create a table newstudent which contains those records of student table who got first division

marks.

Ans.

create table newstudent as(select * from student where div="First")

Q46. For what purposes ALTER TABLE command of mysql can be used?

Ans.

This Command can be used for the following purposes

1. to add a column

2. to add a integrity constraint

3. to redefine a column (datatype, size, default value)

4. to delete a column

Q47. Change the Column name First_name of student table to Firstname

Ans.

Alter Table student change First_name fname varchar(20)

Q48. What is a function in MySQL?

Ans.

A function is a special type of predefined command set that performs some operation and returns a

single value.

Q49. What are the categories of Mysql Functions?

Ans.



There are four categories of MySql Functions

1. String Functions

2. Numeric Functions

3. Date and Time Functions

4. Miscelleneous Functions

Q50 . What is a Data Dictionary ?

Ans.

A data dictionary is a file that contains "metadata" which is data about data. It helps the DBMS to find

various elements of a database while execution of a query.

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