DBMS: Week 05 - Introduction to SQL Query

International Islamic University H-10, Islamabad, Pakistan
Database Managements Systems
Week 05
Introduction to SQL
Engr. Rashid Farid Chishti
http://youtube.com/rfchishti
http://sites.google.com/site/chisht
i

 Definition: Structured Query Language (SQL) is used to interact with and
manipulate databases.
 Purpose:
 Query, update, and manage data
 Define database structures (tables, schemas)
 Control access and permissions
 Key Features:
 Simple and intuitive syntax
 Standardized across most RDBMS
 Highly efficient for large data sets
What is SQL?

 Data Definition Language (DDL): Define and manage database schema
 Commands: CREATE, ALTER, RENAME, TRUNCATE, DROP
 Data Query Language (DQL): Query and retrieve data
 Command: SELECT, DISTINCT
 Data Manipulation Language (DML): Manipulate data in tables
 Commands: INSERT, UPDATE, DELETE
 Data Control Language (DCL): Manage access permissions to users
 Commands: GRANT, REVOKE
 Transaction Control Language (TCL): manages database transactions.
Commands: START, COMMIT, ROLLBACK, SAVEPOINT, SET TRANSACTION
Categories of SQL Commands

 Integer Data Types: Used for storing exact numbers.
Data Types in MySQL
Storage
(Bytes)
Range (Signed) Range (Unsigned)
TINYINT 1 -128 to 127 0 to 255
SMALLINT 2 -32,768 to 32,767 0 to 65,535
MEDIUMINT 3 -8,388,608 to 8,388,607 0 to 16,777,215
INT (INTEGER) 4 -2,147,483,648 to 2,147,483,647 0 to 4,294,967,295
BIGINT 8
-9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
0 to
18,446,744,073,709,55
1,615

 Fixed-Point Types : Used for storing exact numbers with decimal places.
 Floating-Point Types : Used for storing approximate numbers.
Data Types in MySQL
Data Type Storage (Bytes) Description
DECIMAL(p,s)
(NUMERIC)
Varies
Stores exact decimal values. p (precision) is total
digits, s (scale) is decimal places. e.g., DECIMAL(10,2)
stores up to 10 digits with 2 decimal places.
FIXED Varies Synonym for DECIMAL
FLOAT(p)
4 (for p ≤ 24)
8 (for p > 24)
Single-precision floating-point number.
DOUBLE(REAL) 8 Double-precision floating-point number.

 Bitwise Data Type : Used for storing binary values.
 Date and Time Data Types: Used for storing date and time.
Data Types in MySQL
BIT(n) Varies Stores binary values (BIT(8) stores 8 bits).
Data Type
Storage
(Bytes)
Format Description
DATE 3 YYYY-MM-DD
Stores only the date.
Range: 1000-01-01 to 9999-12-31
DATETIME 8 YYYY-MM-DD HH:MM:SS Stores date and time.
TIMESTAMP 4 YYYY-MM-DD HH:MM:SS
Stores date and time
(auto-updates).
TIME 3 HH:MM:SS Stores only time.
YEAR 1 YYYY
Stores only year
Range: 1901 to 2155.

 String (Character) Data Types: Used for storing text data.
Data Types in MySQL
Data Type
Storage
(Bytes)
Description
CHAR(n) Fixed (0-255)
Fixed-length string
CHAR(10) always uses 10 bytes.
VARCHAR(n) Varies (0-65,535)
Variable-length string
VARCHAR(10) uses actual length + 1 byte.
TINYTEXT Up to 255 Small text (up to 255 characters).
TEXT Up to 65,535 Medium Text
MEDIUMTEXT Up to 16,777,215 Large Text
LONGTEXT Up to 4GB Very Large Text

 Binary Types: Used For Storing Files & Encrypted Data.
 Binary objects can be images, audio, videos, etc.
Data Types in MySQL
Data Type
Storage
(Bytes)
Description
TINYBLOB Up to 255 Small binary objects.
BLOB Up to 65,535 Medium binary object.
MEDIUMBLOB Up to 16,777,215 Large binary object.
LONGBLOB Up to 4GB Very large binary object.

 DDL stands for DATA DEFINATION LANGUAGE.
 DDL changes the structure of the table like creating, deleting & altering a table.
 All the command of DDL are auto-committed that means it permanently save
all the changes in the database
 DDL Commands:
 CREATE: Defines new tables, databases, indexes
 ALTER: Modifies existing tables or databases
 ADD, MODIFY, CHANGE, DROP, RENAME.
 TRUNCATE: Deletes all rows from a table
 DROP: Deletes tables or databases
Data Definition Language (DDL)

CREATE: Creates a new database, table, index, or view
RENAME: Renames an existing table
TRUNCATE: Removes all records from a table but keeps its
structure
DROP: Deletes a database, table, index, or view permanently
Data Definition Language (DDL) Commands
ALTER: Modifies an existing table, column, or database
structure
ADD COLUMN: to add a new column to an existing table.
CHANGE COLUMN: modify an existing column's name, data
type
MODIFY COLUMN: change the data type, constraints, or
position of an existing column without renaming it.
DROP COLUMN: Delete a Column, Once dropped, the column
and its data cannot be recovered unless a backup
exists.

 The CREATE command is used to define and create database objects such as
databases, tables, indexes, views, triggers, stored procedures, and users.
 Creating a Database
 Creating a Table
Creating Tables with CREATE Command
DROP TABLE IF EXISTS Student;
CREATE TABLE Student (
id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
age INT,
email VARCHAR(100) UNIQUE
);
CREATE DATABASE student_db; USE
student_db;

 The ALTER command in MySQL is used to modify an existing database object
such as a table, column, index, or constraint.
 Adding a new Column
 Verify column addition
 Renaming a Column
 Verify changes
 Dropping a Column
 Verify changes
Modifying Tables with ALTER Command
ALTER TABLE Student ADD COLUMN gender
VARCHAR(10);
ALTER TABLE Student MODIFY COLUMN age
SMALLINT;
ALTER TABLE Student DROP COLUMN
age;
DESCRIBE
Student;
DESCRIBE
Student;
DESCRIBE
Student;

 Renaming a column
 Verify
 Renaming a table
 Again renaming a table and verify
Modifying Tables with ALTER Command
ALTER TABLE Student CHANGE COLUMN name full_name
VARCHAR(150);
DESCRIBE
Student;
RENAME TABLE Student TO
Students;
SHOW
TABLES;
RENAME TABLE Students TO
Student;
SHOW
TABLES;

 The TRUNCATE command in MySQL is used to remove all rows from a table
while resetting the auto-increment counter (if applicable).
 Key Features:
 Deletes All Data – Unlike DELETE, which requires a WHERE clause to remove specific
rows, TRUNCATE removes all rows.
 Faster than DELETE – It does not log individual row deletions, making it more efficient.
 Resets AUTO_INCREMENT Counter – If the table has an AUTO_INCREMENT column, it
resets to 1.
 Does Not Activate Triggers – Unlike DELETE, TRUNCATE does not execute BEFORE
DELETE or AFTER DELETE triggers.
 Cannot Be Rolled Back in MySQL – Since it is a DDL command, it commits immediately
and cannot be undone with ROLLBACK.
 Truncate a Table:
Using TRUNCATE Command (1/2)
TRUCCATE TABLE

 Add some data first:
 Show data:
 Truncate a table:
 Show data again:
Using TRUNCATE Command (2/2)
TRUCCATE TABLE
Student;
INSERT INTO Student VALUE
(101,'Rashid','chishti@gmail.com','male');
INSERT INTO Student (full_name, email, gender)
VALUE ('Farid','farid@gmail.com','male');
SELECT * FROM Student;
SELECT * FROM Student;

Key Differences: TRUNCATE vs. DELETE vs. DROP
Feature TRUNCATE DELETE DROP
Removes all rows ✅ Yes
✅ Yes
(if no WHERE)
✅ Yes
Can use WHERE
clause
❌ No ✅ Yes ❌ No
Resets auto-
increment
✅ Yes ❌ No ✅ Yes
Affects table
structure
❌ No ❌ No
✅ Yes
(removes table)
Triggers execution ❌ No ✅ Yes ❌ No
Can be rolled back ❌ No (DDL)
✅ Yes
(if inside TRANSACTION)
❌ No
Speed ⚡ Faster 🐢 Slower ⚡ Fastest

 The DROP command in MySQL is used to permanently remove a database
object, such as a table, database, index, or view. This operation cannot be
rolled back.
 Drop a Table and verify deletion of table:
 Drop a database and verify deletion:
 Removing a primary key constraint
 First Remove AUTO_INCREMENT
 Then remove PRIMARY KEY
 Change back to primary key with auto increment
Using DROP Command
DROP TABLE IF EXISTS
student;
SHOW
TABLES;
DROP DATABASE IF EXISTS
student_db;
SHOW
DATABASES;
ALTER TABLE Student MODIFY ID INT;
ALTER TABLE Student DROP PRIMARY
KEY;
DESCRIBE
Student;
ALTER TABLE Student MODIFY ID INT AUTO_INCREMENT PRIMARY

 Data Query Language (DQL) is a subset of SQL (Structured Query Language)
that focuses on retrieving data from a database. It consists of commands used
to query and fetch data from relational databases.
 Key Features of DQL:
 Primarily deals with retrieving data.
 Uses the SELECT statement to fetch records.
 Supports filtering, sorting, grouping, and aggregation.
 Works with clauses like WHERE, ORDER BY, GROUP BY, HAVING, and JOIN
to refine queries.
Data Query Language (DQL)

ASC: Ascending Order
DESC: Descending
Order
ORDER BY: Column Name(s)
HAVING: Condition(s)
GROUP BY : Column Name(s)
WHERE: Condition(s)
JOIN: table ON
table.column
FROM: Name of Table(s)
DISTINCT: Name of Table
SELECT: retrieve data from one or more tables in a
database.
Data Query Language (DQL) Command
LIMIT: Number

First Make a Student Table
DROP TABLE IF EXISTS Student;
CREATE TABLE Student (
id INT AUTO_INCREMENT PRIMARY KEY,
roll_no VARCHAR(20) NOT NULL,
name VARCHAR(50) NOT NULL,
age INT NOT NULL CHECK(Age>=0),
dob DATE NOT NULL DEFAULT (CURDATE()),
degree VARCHAR(30) NOT NULL
);
DROP DATABASE IF EXISTS student_db;
CREATE DATABASE student_db;
USE student_db;

First INSERT Some Data
INSERT INTO Student(ID, Roll_No, Name, Age, DoB, Degree)
VALUES
(1, '3-FET/BSCE/F22', 'Nawal Mudassar', 21, '2003-11-09',
'BSCE' ),
(2, '3-FET/BSCET/F23', 'Waleed Khan', 20, '2005-02-18',
'BSCET'),
(3, '4-FET/BSCE/F22', 'M. Zain Tariq', 21, '2003-08-04',
'BSCE' ),
(4, '4-FET/BSCET/F23', 'Abdul Manan', 22, '2002-10-23',
'BSCET'),
(5, '6-FET/BSCE/F22', 'Haseen Ullah', 19, '2005-03-16',
'BSCE' ),
(6, '6-FET/BSCET/F23', 'Saif Ullah', 19, '2005-11-27',
'BSCET'),
TRUNCATE Student; # Delete all records from Student Table

 The SELECT statement is used to retrieve data from one or more tables.
 Retrieve all columns from a table
 Retrieve specific columns
 Overriding column names
 Sort data using ORDER BY
Using SELECT Command (1/2)
SELECT * FROM
student;
SELECT roll_no, email FROM
student;
SELECT roll_no AS 'Roll Number' FROM
student;
SELECT roll_no AS 'Roll Number', name AS 'Student’s
Name' FROM student;
SELECT * FROM student ORDER BY name
DESC;
SELECT * FROM student ORDER BY name
ASC;
SELECT age, name FROM student ORDER BY age DESC, name
ASC;

 Limit number of rows.
 Get unique values.
 Filter data using WHERE
Using SELECT Command (1/2)
SELECT * FROM student LIMIT
2;
SELECT DISTINCT Age FROM
student;
SELECT * FROM student WHERE ID =
101;
SELECT * FROM student ORDER BY name DESC
LIMIT 3;
SELECT * FROM student ORDER BY name ASC LIMIT
3;

DBMS: Week 05 - Introduction to SQL Query

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