Lecture on DBMS & MySQL.pdf v. C. .

LECTURE ON
Introduction to DBMS &
MySQL
BY: ABHISHEK BHARDWAJ
PGT- COMPUTER SCIENCE

Introduction to DBMS
DBMS
RDBMS
SQL
Database Database is a collection of related data.
Database System = Database + Software
Data is stored in the form of rows and columns, i.e. in a table.
Structured Query Language

Why Database?
Advantages of Database :
 Data Security eg. Database of a banking system, Database of a
Social Networking Site like Facebook.
 Data is arranged in a specific order.
 Data retrieval is too fast.
 Data manipulation becomes very fast.
 Minimized data inconsistency (anomaly or discrepancy) eg.
Student name is saved as “John Asthana” on a main computer of
school but on teacher registered system same student name is “J.
Asthana”

Relational Database Management System (RDBMS)
RDBMS : In Relational Database Management System (RDBMS),
data is stored in the form of rows and columns, i.e. in a table.
Example: A table named ‘Student’ is shown below
Roll No Name Class Gender
3204 Ram IX M
3205 Sita X F
3206 Mohan XI M
Total Rows/ Tuples/ Cardinality : 03
Total Columns/ Degree : 04
Student
Terms in Relational DB
Ser Term
Terminology in
RDBMS
1. Table Relation
2. Rows Tuples
3. Columns Attribute
4. Pool of Values Domain
NOTE :
(i) Headings are not included in the
counting of rows.
(ii) For attribute Gender, character
values F / M are called domain.

MySQL Installation for Windows
https://www.mysql.com/ : Copy this link in a Browser
Click Here
Click Here

Click Here
Click Here

Click Here
Download
Double Click on downloaded file to run setup.
Click Here

Database Management System (DBMS)
“A DBMS is a collection of programs that enables the users to
create and maintain the database”.
 Hence DBMS is a general-purpose software system that
facilitates the processes of defining, constructing and
manipulating databases for various applications.
 Defining a database involves specifying the data types,
structures and constraints for the data to be stored in the
database.
 Constructing is the process of storing the database itself on
some storage medium that is controlled by the DBMS.
 Manipulating includes such functions as querying the database
to retrieve specific data, updating the database to reflect
changes in the mini world, and generating reports from the data.

Database Management System (DBMS)

Purpose/ Intended Uses of a DBMS
Controlling Redundancy and removing Data Inconsistency : Data
duplication is not possible in DBMS as data is stored at one place
in the database and accessed through a unique key. It also
controls the inconsistency of data i.e. multiple copies of same
data.
Restricting unauthorized access : Multiple users can share a
database at a same time but all users will not be authorized to
access all information in the database because of role of each
user is already defined.
Providing multiple user interface : Casual (random) users may
interact using query language, application programmers uses
programming language interface and menu driven interfaces or
natural languages interface is used for standalone users.

Purpose/ Intended Uses of a DBMS
Enforcing integrity constraints : We can apply certain integrity
constraints that must hold for the data.
e.g. The value of ‘Name’ in STUDENT record must be an string of
no more than 30 alphabetic characters.
Backup and recovery : Provides facility for recovering from
hardware or software failures.
 The backup and recovery subsystem of a DBMS is responsible
for recovery.

SQL (Structured Query Language)
SQL stands for Structured Query Language. It is used to create a
database, which will be there in the form of rows and columns
i.e. in a table.
SQL is a collection of different commands & for every task we
have a command.
All the SQL commands are divided into four sections/Processing
capabilities of SQL :
(i) DDL (Data Definition Language)
(ii) DML (Data Manipulation Language)
(iii) TCL (Transaction Control Language)
(iv) DCL (Data Control Language)

DDL (Data Definition Language) :
 DDL use commands to create or modify existing structure of
database objects like create, alter, drop or truncate database
objects in database. In SQL server following operations will
come under DDL operations.
CREATE – By using this operation we can create objects (like
Tables, procedures, etc…) in database.
ALTER – We can modify objects (like Tables, procedures,
etc…) in database.
DROP – We can drop or delete objects in database.
TRUNCATE – It will delete all the records from table and it
will reset identity of column to initial value.
A database object is any defined object in a database that is used to store or reference
data. Anything which we make from create command is known as Database Object.

DML (Data Manipulation Language) :
 DML use commands to perform multiple operations like
insert, update, retrieve and delete data in database.
 In SQL server following operations will come under DML
operations.
INSERT – By using this operation we can insert data in
table.
SELECT – We can get or retrieve data from table.
DELETE – We can delete data from table.
UPDATE – We can update data in the table.

TCL (Transaction Control Language) :
 TCL use commands to perform multiple transactional
operations like commit, rollback, save transactions in
database.
 In SQL server following operations will come under TCL
operations.
COMMIT – By using this operation we can save work we
done in transactions.
ROLLBACK – We can rollback database to original state
before COMMIT operation on transactions.
SAVE TRANSACTION – We can set save point in transactions.

DCL (Data Control Language) :
 DCL use commands to secure database objects by creating
roles, permissions using GRANT, REVOKE operations in
database.
 In SQL server following operations will come under DCL
operations.
GRANT – By using this operation we can create access
permissions for users to database.
REVOKE – We can rollback or take back user access
permissions for database.

Characteristics of SQL
(i) SQL is easy to learn.
(ii) SQL is used to access data from relational database
management systems.
(iii) SQL can execute queries against the database.
(iv) SQL is used to describe the data.
(v) SQL is used to define the data in the database and
manipulate it when needed.
(vi) SQL is used to create and drop the database and table.
(vii) SQL is used to create a view, stored procedure, function in a
database.
(viii) SQL allows users to set permissions on tables, procedures,
and views.

Data Types of SQL
Following are some important data types of SQL :
char : char stores only fixed-length character string
(1-255 characters) data types. Use this when
the length of the characters are concise and
known.
varchar : varchar stores variable-length string where
an upper limit of length (65535 characters) is
specified. Use this when the data entries
length is varying.
integer : Stores integer value.
decimal : Stores decimal value.
date : Stores date in year, month, and day.
time : Stores time in hour, minute, and second.

SQL Constraints
Constraints : Constraints are set of rules that are applied to a
table. Constraints enforce limits to the data or type of data
that can be inserted/updated/deleted from a table. The
whole purpose of constraints is to maintain the data
integrity during an update/delete/insert into a table.
Some important SQL constraints are :
(i) Primary Key
(ii) Unique
(iii) NOT NULL
(iv) Default
(v) Check
(vi) Foreign Key

SQL Constraints
 Primary Key constraint states that a field/ attribute/ column
cannot contain duplicate value and it can’t be left blank. It
must uniquely identify each row.
Employee
 In Employee table Emp_Code is Primary Key and this field
does not contain any duplicate value as well as it must not
left with blank.
Emp_Code Emp_Name Emp_Salary
101 Ram 20,000
102 Ravi 25,0000
103 Mohan 15,000
Primary Key = Unique + NOT NULL

SQL Constraints
 Unique constraint states that a field/ attribute/ column
cannot contain duplicate value. UNIQUE constraint enforces
a column or set of columns to have unique values.
Employee
 In Employee table Mobile_No. is Unique, now this field does
not contain any duplicate value but can be left with blank
(null values).
Emp_Code Emp_Name Emp_Salary Mobile_No.
101 Ram 20,000 9925223311
102 Ravi 25,0000 null
103 Mohan 15,000 8906204482

SQL Constraints
 NOT NULL constraint states that a field/ attribute/ column
cannot be left blank. It is used to ensure that a given column
of a table is never assigned the null value.
Employee
 In Employee table if Salary is assigned as NOT NULL
constraint, then this field can’t be left with blank (null
values).
Emp_Code Emp_Name Emp_Salary Mobile_No.
101 Ram 20,000 9925223311
102 Ravi 25,0000 null
103 Mohan 15,000 8906204482

SQL Constraints
 Default constraint states that a field/ attribute/ column may
be given a default value when no values are specified for
that column.
Employee
 In Employee table if Gender is assigned as Default constraint
with value ‘M’, and if no other value is specified in any of the
records then default value ‘M’ will be added to all new
records.
Emp_Code Emp_Name Emp_Salary Mobile_No. Gender
101 Ram 20,000 9925223311 M
102 Rashmi 25,0000 null F
103 Mohan 15,000 8906204482 M

SQL Constraints
 Check constraint states that a field/ attribute/ column can be
checked for a particular condition before entering it into the
table. It will allow only certain values for this column.
Employee
 In Employee table if Emp_Salary is assigned as Check
constraint with a condition Emp_Salary > 10,000, then values
<= 10,000 cannot be assigned to this particular field.
Emp_Code Emp_Name Emp_Salary Mobile_No. Gender
101 Ram 20,000 9925223311 M
102 Rashmi 25,0000 null F
103 Mohan 15,000 8906204482 M

SQL Constraints
 Foreign Key : A Foreign Key is a field (or collection of fields) in
one table, that refers to the Primary Key in another table. The
table with the foreign key is called the child table, and the table
with the primary key is called the referenced or parent table.
The keyword used to create Foreign Key is called references.
Employee Department
 In Employee table Dept_Code is Non Primary Key, while in
Department table Dept_Code is Primary Key. Dept_Code in
Employee table will be treated as Foreign Key.
Emp_Code Emp_Name Dept_Code
101 Ram 2001
102 Rashmi 2001
103 Mohan 2002
Dept_Code Dept_Name
2001 Computer
2002 Biology
2003 Maths

SQL Commands
(CREATE DATABASE)
CREATE DATABASE : This command is used to create database.
Remember that a database is a logical concept.
eg. by using this command a database named employee will be
created on a portion of our hard disk, on which we may create
multiple tables related to this database.
Syntax : mysql> CREATE DATABASE database_name;

SQL Commands
(USE Database)
USE Database : This command is used to select a database. A
database needs to be created only once, but must be selected for
use each time, we begin a mysql session.
eg. by using this command a database named employee will be
selected.
Syntax : mysql> USE database_name;

SQL Commands
(SHOW DATABASES)
SHOW DATABASES : This command list all databases in mysql.
Syntax : mysql> SHOW DATABASES;

SQL Commands
(CREATE TABLE)
After creating database employee, now if we want to create
table emp by the selecting data base employee, then we must
decide the structure of table emp in advance.
Emp_Code Emp_Name Emp_Designation Emp_Mobile Emp_Salary Emp_DOJ
emp
Creating a table means, creating the structure of the table with
column names and its type of data along with their length, which
particular column will hold.
int varchar(50) varchar(40) char(10) decimal date

SQL Commands
(CREATE TABLE)
CREATE TABLE : The statement is used to create a new table in a
database.
Syntax : mysql> CREATE TABLE table_name(
column1 datatype contraint,
……….
);
Constraint is optional. It may be added as per requirement.

SQL Commands
(CREATE TABLE)
CREATE TABLE : The statement is used to create a new table in a
database.

SQL Commands
(SHOW TABLES)
SHOW TABLES : The statement is used to get a list of the tables in
a mysql database.
eg. In our previous example we have created a table emp under
employee database, so after using this command list of all tables
under employee database will be displayed.
Syntax : mysql> SHOW TABLES;

SQL Commands
(INSERT INTO)
INSERT INTO : The INSERT INTO statement is used to insert new
records (row) in a table.
It is possible to write the INSERT INTO statement in two ways:
Syntax -1 : mysql> INSERT INTO table_name
VALUES(value1, value2, value3,……..);
Syntax-1 is used when, we have values for each field. If not so, use Syntax-2.

SQL Commands
(INSERT INTO)
INSERT INTO : The INSERT INTO statement is used to insert new
records (row) in a table.
Syntax-2:
mysql> INSERT INTO table_name (column1, column2,...)
VALUES (value1, value2, ...);
• In Syntax-2 select the columns/fields then assign values in the sequence of fields.
• Only those fields can be left in Syntax-2 which do not have constraint NOT NULL.

SQL Commands
(UPDATE)
UPDATE : The UPDATE statement is used to modify the existing
records in a table.
Syntax : mysql> UPDATE table_name
SET field1=value1, field2=value2,….
WHERE condition;
• WHERE clause is used because if, condition is not added, then, all employees having salary
=70000 will be updated to salary=90000.

SQL Commands
(ALTER)
ALTER : The ALTER statement is used to add, delete, or modify
columns in an existing table.
 The ALTER TABLE statement is also used to add and drop
various constraints on an existing table
Syntax to ADD column/field :
mysql> ALTER TABLE table_name
ADD column_name data type;
• After ADDING column/ field, it is required to fill values with respect to that
field in each record.
• Data type char by default takes 1 character , so we may write it as char(1)
or simply char, while executing query on SQL prompt.

SQL Commands
(ALTER)
Syntax to ADD column/field : To add a column in a table.
ADD column_name data type;
ADDING new column in existing
table emp.
UPDATING record wrt new
column in existing table emp.

SQL Commands
(ALTER)
Syntax to DROP column/field : To delete a column in a table.
DROP column_name;
Column deleted after
drop statement.

SQL Commands
(ALTER)
Syntax to MODIFY column/field : To change the data type of a
column in a table.
MODIFY column_name data type;

SQL Commands
(ALTER)
Syntax to RENAME column/field for MySQL version 5.7 :
CHANGE old_column_name new_column_name data type;
Syntax to RENAME Column in MySQL 8.0 :
ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name;

SQL Commands
(DESCRIBE)
DESCRIBE/ DESC : The DESC is the short form of DESCRIBE
command and used to display the information about a table like
column names and constraints on column name.
Syntax : mysql> DESC table_name;
The DESCRIBE/ DESC command is equivalent to the following command :
Syntax : mysql> SHOW COLUMS FROM table_name;

SQL Commands
(SELECT)
SELECT : The SELECT statement is used to select data from a
database. The data returned is stored in a result table, called the
result-set.
Syntax 1: mysql> SELECT * FROM table_name;

SQL Commands
(SELECT)
SELECT : The SELECT statement is used to select data from a
database. Here, column1, column2, ... are the field names of the
table, we want to select data from.
Syntax 2:
mysql> SELECT column1, column2, … FROM table_name;

SQL Commands
(SELECT with WHERE clause)
SELECT with WHERE clause : The WHERE clause is used to filter
records. It is used to extract only those records that fulfill a
specified condition.
Syntax 3: mysql> SELECT * FROM table_name WHERE condition;
WHERE clause is not only used in SELECT statements, it is also used in UPDATE, DELETE, etc.!

SQL Commands
(Examples of SELECT with WHERE clause)
 Select the list of all the employees having salary >90000.

SQL Commands
 Display the list of all the employees, who have joined before
2022.

SQL Commands
 Display the list of all the employees, who have been
appointed as Developer.

SQL Commands
2022 AND have salary<100000.
MySQL logical AND operator compares two expressions and returns true if both of the
expressions are true.

SQL Commands
2022 OR have salary<100000.
MySQL logical OR operator compares two expressions and returns true if any of the
expressions is true.

SQL Commands
 Display the list of all the employees, who have salary in
between 80000 - 100000.

SQL Commands
(SELECT DISTINCT)
SELECT DISTINCT : The SELECT DISTINCT statement is used to
return only distinct (different) values.
Inside a table, a column often contains many duplicate values;
and DISTINCT keyword list the different (distinct) values.
Syntax: mysql> SELECT DISTINCT column1, column2, ...
FROM table_name;

SQL Commands
(BETWEEN)
BETWEEN : The BETWEEN operator selects values within a given
range. The values can be numbers, text, or dates.
The BETWEEN operator is inclusive : begin and end values are
included.
Syntax: mysql> SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

SQL Commands
(IN Operator)
IN : The IN operator allows you to specify multiple values in
a WHERE clause.
The IN operator is a shorthand for multiple OR conditions.
Syntax : mysql> SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1, value2, ...);

SQL Commands
(NOT IN Operator)
NOT IN : The NOT operator negates the IN operator.
Syntax : mysql> SELECT column_name(s)
FROM table_name
WHERE column_name NOT IN (value1, value2, ...);

SQL Commands
(Pattern Matching & LIKE Operator)
SQL pattern matching enables us to use _ to match any single
character and % to match an arbitrary number of characters
(including zero characters). In MySQL, SQL patterns are case-
insensitive by default.
LIKE :The LIKE operator is used in a WHERE clause to search for a
specified pattern in a column.
There are two wildcards often used in conjunction with
the LIKE operator:
(a) The percent sign (%) represents zero, one, or multiple
characters.
(b) The underscore sign (_) represents one, single character
The percent sign and the underscore can also be used in combinations!
NOT LIKE : NOT operator negates the LIKE operator.

SQL Commands
Syntax : mysql> SELECT * FROM table_name
WHERE column LIKE pattern;
Examples of LIKE Operator :
LIKE Operator Description
WHERE Emp_Name LIKE 'a%' Finds any values that start with "a"
WHERE Emp_Name LIKE '%a' Finds any values that end with "a"
WHERE Emp_Name LIKE '%or%' Finds any values that have "or" in any
position
WHERE Emp_Name LIKE '_r%' Finds any values that have "r" in the second
position
WHERE Emp_Name LIKE 'a_%' Finds any values that start with "a" and are
at least 2 characters in length
WHERE Emp_Name LIKE 'a_ _%' Finds any values that start with "a" and are
at least 3 characters in length
WHERE Emp_Name LIKE 'a%o' Finds any values that start with "a" and ends
with "o"

SQL Commands
After A here are 4 Underscores to
match with Designation – Admin
If there is no match in record, then it
shows Empty Set as output.

SQL Commands
(Foreign Key Concept)
Foreign Key : The foreign key is used to link one or more than one
table together.
 It is also known as the referencing key.
 A foreign key matches the primary key field of another table.
 It means a foreign key field in one table refers to the primary
key field of the other table.
 It identifies each row of another table uniquely that
maintains the referential integrity in MySQL.
MySQL defines the foreign key in two ways:
 Using CREATE TABLE Statement
 Using ALTER TABLE Statement

SQL Commands
(Foreign Key Theory Concept Not to be written in Exam)
Using CREATE TABLE (Method-1) : Use it, when, we are declaring
Foreign Key at the time of Creating New Table.
E_Code E_Name E_Salary Dept_Code
child
Dept_Code Dept_Name Dept_HoD
parent
Foreign Key
Primary Key
Primary Key
1. Data type of Dept_Code field must be same in both tables i.e. here it is declared as INTEGER.
2. REFERENCES keyword is used in child table to make Dept_Code Foreign Key for parent table.
3. Dept_Code in child table REFERENCES Dept_Code in parent table (parent.Dept_Code) which
creates a connection between two tables i.e. parent and child table.

SQL Commands
(Foreign Key Practical Concept For Exam Purpose)
Using CREATE TABLE (Method-2) : Use it, when, we are declaring
Foreign Key at the time of Creating New Table.
child
parent
Foreign Key
Primary Key
Primary Key

SQL Commands
(Foreign Key Concept)
Using ALTER TABLE : Use it, when, we have existing tables and
want to ADD constraint Foreign Key.
children
parents
Foreign Key
Primary Key
Primary Key

SQL Commands
(MySQL Functions)
MySQL Functions : MySQL has many built-in functions.
This reference contains string, numeric, date and time, functions
in MySQL.
1. String / Char Function
2. Numeric Function
3. Date & Time Function

SQL Commands
(MySQL Functions – String / Char Function)
CHAR() : MySQL CHAR() returns the character value of the given
integer value according to the ASCII table. It ignores the NULL
value.
Example : SELECT CHAR(65);
Output : A
Example : SELECT CHAR(67,72,65,82);
Output : CHAR

SQL Commands
CONCAT() : Adds two or more expressions together.
Example : SELECT CONCAT(“MEERA”, “DESAI”);
Output : MEERADESAI

SQL Commands
LOWER() / LCASE() : Converts a string to lower-case.
Example : SELECT LCASE(“I LOVE MY COUNTRY”);
Output : i love my country

SQL Commands
UPPER() / UCASE() : Converts a string to upper-case.
Example : SELECT UCASE(“i love my country”);
Output : I LOVE MY COUNTRY

SQL Commands
SUBSTR() : Extracts a substring from a string (starting at any
position).
Syntax : SUBSTRING(string, position, no_of_characters)
Example : SELECT SUBSTR(“MOHAN”,3, 3 );
Output : HAN
-3 will be counted from
last character of the
string i.e. N but after
counting -3 from last
character, 3 characters
of substring will taken in
sequence i.e. HAN

SQL Commands
LTRIM() : Removes leading spaces from a string.
Syntax : LTRIM(string)
Example : SELECT LTRIM(“ MOHAN” );
Output : MOHAN

SQL Commands
RTRIM() : Removes trailing spaces from a string.
Syntax : RTRIM(string)
Example : SELECT RTRIM(“MOHAN ” );
Output : MOHAN

SQL Commands
TRIM() : Removes leading and trailing spaces from a string.
Syntax : TRIM(string)
Example : SELECT TRIM(“ MOHAN ” );
Output : MOHAN
Removing Leading
Character “X” from the
String.
Removing Trailing
Character “X” from the
String.
Removing Trailing &
Leading Character “X”
from the String.

SQL Commands
INSTR() : Returns the position of the first occurrence of a string in
another string. If string2 is not found, this function returns 0.
Syntax : INSTR(string1, string2)
Example : SELECT INSTR(“MOHAN”, “HAN” );
Output : 3

SQL Commands
LENGTH() : Returns the length of a string (in bytes).
Syntax : LENGTH(string)
Example : SELECT LENGTH(“MOHAN” );
Output : 5

SQL Commands
LEFT() : Extracts a number of characters from a string (starting
from left).
Syntax : LEFT(string, number_of_chars)
Example : SELECT LEFT(“MOHAN”, 4 );
Output : MOHA
If this parameter is
larger than the
number of characters
in string, this function
will return string.

SQL Commands
RIGHT() : Extracts a number of characters from a string (starting
from right).
Syntax : RIGHT(string, number_of_chars)
Example : SELECT RIGHT(“MOHAN”, 4 );
Output : OHAN
If this parameter is
larger than the
number of characters
in string, this function
will return string.

SQL Commands
MID() : Extracts a substring from a string (starting at any
position)
Syntax : MID(string, start_pos, number_of_chars)
Example : SELECT MID(“MOHAN”, 2, 3 );
Output : OHA
The start position, Can
be both a positive or
negative number. If it is a
positive number, this
function extracts from the
beginning of the string. If
it is a negative number,
this function extracts
from the end of the string

SQL Commands
(MySQL Functions – Numeric Function)
MOD() : Returns the remainder of a number divided by another
number.
Syntax : MOD(x, y)
Example : SELECT MOD(5, 2);
Output : 1
If the divisor is zero,
The MOD (dividend,
0) returns NULL.

SQL Commands
POWER()/POW() : Returns the value of a number raised to the
power of another number.
Syntax : POW(x, y)
Example : SELECT POW(5, 2);
Output : 25

SQL Commands
ROUND() : Rounds a number to a specified number of decimal
places.
Syntax : ROUND(number, decimal_places)
Example : SELECT ROUND(15.567, 2);
Output : 15.57
Nearest TENS
Nearest HUNDRED
Nearest THOUSAND

SQL Commands
SIGN() : Returns the sign of a number.
If number > 0, it returns 1
If number = 0, it returns 0
If number < 0, it returns -1
Syntax : SIGN(number)
Example : SELECT SIGN(15);
Output : 1

SQL Commands
SQRT() : Return the square root of a number
Syntax : SQRT(number)
Example : SELECT SQRT(64);
Output : 8

SQL Commands
TRUNCATE() : The TRUNCATE() function truncates (to make something
shorter) a number to the specified number of decimal places.
Syntax : TRUNCATE(number, decimals)
Example : SELECT TRUNCATE(15.565);
Output : 15.56
Nearest TENS
Nearest HUNDRED
Nearest THOUSAND

SQL Commands
Implementation of TRUNCATE() on a Table Column :
TRUNCATE() can be used with other function like AVG(), which will calculate the AVERAGE
SALARY of a particular department . Also TRUNCATE() function can be used to view records of
numeric data to the specified number of decimal places.

SQL Commands
(MySQL Functions – Date & Time Function)
CURDATE()/ CURRENT_DATE() : Returns the current date.
Syntax : CURDATE() /CURRENT_DATE()
Example : SELECT CURDATE();
Output : 2022-03-18
The date is returned as "YYYY-MM-DD" (string) or as YYYYMMDD (numeric)
format depending on whether numeric or string is used in the function.
* Result is depending upon
current System date.
* Result is depending upon
current System date.

SQL Commands
Ques : Display the date after 10 days from the Current Date.
Ques : Display the date before 10 days from the Current Date.
Syntax : SELECT DATE_ADD(DATE, INTERVAL N DAY);
Syntax : SELECT DATE_SUB(DATE, INTERVAL N DAY);

SQL Commands
DATE() : Extracts the date part from a date-time expression.
Returns NULL if expression is not a date or a date-time.
Syntax : DATE()
Example : SELECT DATE(“2022-03-18 10:50:00”);
Output : 2022-03-18
In database many entries are done in date and time stamp format. This format is used to
extract date from that format.

SQL Commands
MONTH() : Returns the month part for a given date.
Syntax : MONTH()
Example : SELECT MONTH(“2022-03-18”);
SELECT MONTH(CURDATE());
Output : 3

SQL Commands
MONTHNAME() : The MONTHNAME() function returns the name
of the month for a given date.
Syntax : MONTHNAME()
Example : SELECT MONTHNAME(“2022-03-18”);
SELECT MONTHNAME(CURDATE());
Output : MARCH

SQL Commands
DAY() : Return the day of the month for a date.
Syntax : DAY()
Example : SELECT DAY(“2022-03-18”);
SELECT DAY(CURDATE());
Output : 18

SQL Commands
DAYNAME() : Returns the weekday name for a given date.
Syntax : DAYNAME()
Example : SELECT DAYNAME(“2022-03-18”);
SELECT DAYNAME(CURDATE());
Output : FRIDAY

SQL Commands
YEAR() : Returns the year part for a given date.
Syntax : YEAR()
Example : SELECT YEAR(“1983-02-08”);
SELECT YEAR(CURDATE());
Output : 1983, 2022

SQL Commands
DAYOFMONTH() : Returns the day of the month for a given date.
Syntax : DAYOFMONTH()
Example : SELECT DAYOFMONTH(“2022-03-18”);
Output : 18
DAY() and DAYOFMONTY() both returns the Day of a given date, but the difference is DAY()
returns the Day of a particular date, while DAYOFMONTH() returns the day in terms of ‘nth ‘
day of the month.

SQL Commands
DAYOFWEEK() : Returns the weekday index for a given date.
Syntax : DAYOFWEEK()
Example : SELECT DAYOFWEEK(“2022-03-18”);
Output : 6
1ST DAY OF WEEK IS SUNDAY.

SQL Commands
DAYOFYEAR() : Returns the day of the year for a given date.
Syntax : DAYOFYEAR()
Example : SELECT DAYOFYEAR(“2022-03-18”);
Output : 77

SQL Commands
NOW() : Returns the current date and time.
Syntax : NOW()
Example : SELECT NOW();
Output : 2022-03-18 11:50:00

SQL Commands
SYSDATE() : Return the current date and time.
Syntax : SYSDATE()
Example : SELECT SYSDATE();
Output : 2022-03-18 11:52:50

SQL Commands
Difference between NOW() and SYSDATE() : The output of both of
them depends upon the execution time.
 NOW() function returns a steady (fix) time that indicates the
time at which the particular statement began to execute.
 SYSDATE() function returns the accurate time at which the
statement executes.

SQL Commands
(Two Types of SQL Functions)
Functions
Multiple- row
functions
Single- row
functions
String Function
Numeric Function
Date Function
Aggregate Function
• Single-row functions operate on single row only and return one result per row.
• Multiple-row functions can manipulate groups of rows to give one result per group of rows.
These functions are also known as group functions.

SQL Commands
(MySQL Functions – Aggregate Function)
AVG() : The AVG() function returns the average value of a
numeric column.
Syntax : SELECT AVG (column_name) FROM table_name
WHERE condition;

SQL Commands
MAX() : The MAX() function returns the largest value of the
selected column.
Syntax : SELECT MAX (column_name) FROM table_name
WHERE condition;

SQL Commands
Ques : Display the details of the employee, getting MAX Salary.
Syntax : SELECT * FROM table_name
WHERE column_name=(SELECT MAX (column_name)
FROM table_name);
Nested Query

SQL Commands
MIN() : The MIN() function returns the smallest value of the
selected column.
Syntax : SELECT MIN (column_name) FROM table_name
WHERE condition;

SQL Commands
Ques : Display the details of the employee, getting MIN Salary.
Syntax : SELECT * FROM table_name
WHERE column_name=(SELECT MIN (column_name)
FROM table_name);
Nested Query

SQL Commands
COUNT() : The COUNT() function returns the number of rows that
matches a specified criterion.
Syntax : SELECT COUNT (column_name) FROM table_name
WHERE condition;
Returns Nos. of
Records/ Rows
in a Table.
Returns Nos. of
Records/ Rows who
have salary<100000.

SQL Commands
SUM() : The SUM() function returns the total sum of a numeric
column.
Syntax : SELECT SUM (column_name) FROM table_name
WHERE condition;
Sum of Salary of
employees, having,
Emp_Code BETWEEN
101 AND 103
Sum of Salary of all
employees.

SQL Commands
(ALTERNATE KEY)
ALTERNATE KEYS : is a column or group of columns in a table that
uniquely identify every row in that table.
 A table can have multiple choices for a primary key but only one
can be set as the primary key.
 All the keys which are not primary key are called an Alternate Key.
Example:
In this table, StudID, Roll No, Email are qualified to become a primary
key. But since StudID is the primary key, Roll No, Email becomes the
alternative key.

SQL Commands
(CANDIDATE KEY)
CANDIDATE KEYS : is a set of attributes that uniquely identify tuples in
a table.
The Primary key should be selected from the candidate keys.
Every table must have at least a single candidate key.
A table can have multiple candidate keys but only a single primary key.
Properties of Candidate key:
 It must contain unique values.
 Must not contain null values.
 Uniquely identify each record in a table.

SQL Commands
(ADD PRIMARY KEY)
ADD PRIMARY KEY : Creates Primary Key constraint on the table.
Syntax : mysql> ALTER TABLE table_name
ADD PRIMARY KEY (column_name);

SQL Commands
(REMOVE PRIMARY KEY)
DROP PRIMARY KEY : Removes Primary Key constraint from the
table.
Syntax : mysql> ALTER TABLE table_name DROP PRIMARY KEY;

SQL Commands
(DELETE RECORD/ROW/TUPLE)
DELETE : The DELETE statement is used to delete existing records
in a table.
Syntax : mysql> DELETE FROM table_name WHERE CONDITION;
Be careful when deleting records in a table! If you omit
the WHERE clause, all records in the table will be deleted!
DELETE FROM STUD;
QUERY WILL DELETE
ALL THE RECORDS AT
ONCE.

SQL Commands
(GROUP BY)
GROUP BY : GROUP BY clause is used to collect data from
multiple records and group the result by one or more column.
 It is generally used in a SELECT statement.
 We can also use some aggregate functions like COUNT, SUM,
MIN, MAX, AVG etc. on the grouped column.
Syntax : mysql> SELECT column(s), AGGREGATE function
FROM table_name
WHERE condition
GROUP BY column;
Continue……

SQL Commands
(GROUP BY)
Query : Count repetitive number of Employees’ names in
EMP_NAME column from database table EMP.

SQL Commands
(ORDER BY)
ORDER BY : Using the ORDER BY clause, we can sort the records
in ascending or descending order as per our requirement.
 The records will be sorted in ascending order whenever
the ASC keyword is used with ORDER BY clause.
 DESC keyword will sort the records in descending order.
If no keyword is specified after the column based on which we
have to sort the records, in that case, the sorting will be done by
default in the ascending order.
Syntax : mysql> SELECT Column_Name(s)
FROM Table_Name
ORDER BY Column_Name ASC/DESC;
Continue……

SQL Commands
(ORDER BY)
Query : Sort the records in the descending order by using sorting
on EMP_ID column from the EMP table.

SQL Commands
(GROUP BY VS. ORDER BY)
 The GROUP BY clause is applicable when we want to use
aggregate functions to more than one set of rows.
 The ORDER BY clause is applicable when we want to get the
data obtained by a query in the sorting order.

Lecture on DBMS & MySQL.pdf v. C. .

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