This document provides an overview of SQL and database management. It begins by outlining the learning objectives which are to change database table structures and retrieve data from databases. It then provides examples of SQL queries for altering tables, retrieving data using SELECT statements, and joining tables. It demonstrates queries for selecting, updating, and altering data as well as using functions, operators, and joins. Tables are created and sample data is inserted to demonstrate example queries.

1. SQL - 1
DSE003 – DATABASE MANAGEMENT SYSTEM
HASANKA WIJESINGHE M I T, B . S c
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2. Learning Outcomes
End of this lesson student will be able to
Change structure of database tables
Retrieve data from database
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3. Create Query
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4. SQL Not Null
 By default, MySQL can hold NULL values.
 The NOT NULL constraint enforces a column to NOT accept NULL values
 SQL NOT NULL on create table
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
Age int
);
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5. SQL Not Null cont.
 SQL NOT NULL on alter table
ALTER TABLE Persons MODIFY COLUMN Age int NOT NULL;
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6. Alter Query
CHANGE STRUCTURE OF DATABASE TABLES
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7. Add New Column
Syntax:
ALTER TABLE [table_name] ADD [column_name] [datatype][size];
Ex:
ALTER TABLE Customers ADD Email varchar(255);
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8. Delete Column
 Syntax:
ALTER TABLE [table_name] DROP COLUMN [column_name];
Ex:
ALTER TABLE Customers DROP COLUMN Email;
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9. Remove Primary Key
 Syntax:
ALTER TABLE [table_name] DROP PRIMARY KEY;
Ex:
ALTER TABLE Customers DROP PRIMARY KEY;
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10. Add Primary Key
 Syntax:
ALTER TABLE [table_name] ADD PRIMARY KEY ([column name]);
Ex:
ALTER TABLE Customers ADD PRIMARY KEY (id);
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11. Add Foreign Key
 Syntax:
ALTER TABLE [table_name] ADD FOREIGN KEY ([column name]) REFERENCES [reference
table]([column name]);
Ex:
ALTER TABLE Orders ADD FOREIGN KEY (PersonID) REFERENCES
Persons(PersonID);
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12. Select Query
RETRIEVE DATA FROM DATABASE TABLES
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13. Retrieve All Data
 Syntax:
SELECT * FROM [table name];
Ex:
SELECT * FROM customers;
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14. Retrieve Selected Columns
 Syntax:
SELECT [column name],[column name],…. FROM [table name];
Ex:
SELECT c_id, c_name FROM customers;
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15. Select with WHERE Clause
 Syntax:
SELECT [column name],[column name],…. FROM [table name] WHERE [condition];
Ex:
SELECT * FROM customers WHERE c_id = 1;
SELECT order_id FROM orders WHERE qty > 5;
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16. Select with LIMIT Clause
 Syntax:
SELECT [column name],[column name],…. FROM [table name]
WHERE [condition]
LIMIT [number];
Ex:
SELECT * FROM customers LIMIT 5;
SELECT order_id FROM orders WHERE qty > 5 LIMIT 2;
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17. Select with MIN() Function
 Syntax:
SELECT MIN([column name]) FROM [table name]
WHERE [condition];
Ex:
SELECT MIN(qty) FROM orders WHERE order_id = 2;
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18. Select with MAX() Function
 Syntax:
SELECT MAX([column name]) FROM [table name]
WHERE [condition];
Ex:
SELECT MAX(qty) FROM orders WHERE order_id = 2;
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19. Select with COUNT() Function
 Syntax:
SELECT COUNT([column name]) FROM [table name]
WHERE [condition];
Ex:
SELECT COUNT(qty) FROM orders WHERE order_id = 2;
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20. Select with AVG() Function
 Syntax:
SELECT AVG([column name]) FROM [table name]
WHERE [condition];
Ex:
SELECT AVG(qty) FROM orders WHERE order_id = 2;
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21. Select with SUM() Function
 Syntax:
SELECT SUM([column name]) FROM [table name]
WHERE [condition];
Ex:
SELECT SUM(qty) FROM orders WHERE order_id = 2;
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22. Select with LIKE operator
 Syntax:
SELECT [column name], [column name],… FROM [table name]
WHERE [column name] LIKE [pattern];
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Like Operator Description
WHERE [column name] LIKE 'a%' Finds any values that start with "a"
WHERE [column name] LIKE '%a' Finds any values that end with "a"
WHERE [column name] LIKE ‘%or%' Finds any values that have "or" in any position
WHERE [column name] LIKE ‘_r%' Finds any values that have "r" in the second position
WHERE [column name] LIKE 'a_%' Finds any values that start with "a" and are at least 2 characters in length
WHERE [column name] LIKE 'a__%' Finds any values that start with "a" and are at least 3 characters in length
WHERE [column name] LIKE 'a%o' Finds any values that start with "a" and ends with "o"

23. emp_no name address emp_district emp_dep contact_no Salary des
A0001 Kamal Perera Temple Road,
Homagama
Colombo Finance 0771234567 75000/= Accountant
A0002 Namal de
Silva
Main Street,
Badulla
Badulla Sales 0711234567 65000/= Group
Leader
A0003 Nimali Peries New Town,
Embilipitiya
Ratnapura Finance 0781234567 78000/= Manager
A0004 Kasun
Wijesinghe
New Town,
Ratnapura
Ratnapura HR 0721234567 25000/= Trainee
A0005 Ridmi Perera Galle Road,
Moratuwa
Colombo Marketing 0781234566 50000/= Manager
A0006 Nalin Peries Jaffna Road,
Anuradhapura
Anuradhapura Transport NULL 35000/= Driver
Emp_details
Create following table and insert data

24. 1. Show all employee details
2. Show name and designation of the employees
3. Show details of Finance Department employees
4. Display employee details in descending salary order
5. Display the total number of employees
6. Display max salary
7. Display min salary
8. Display average salary
9. List the number of employees in each district
10. List more than two employees in each department

25. JOIN QUERY
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26. Join Query
 LEFT JOIN
 RIGHT JOIN
 INNER JOIN
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27. Create following table and insert data
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emp_no name address emp_district emp_dep contact_no Salary des
A0001 Kamal Perera Temple Road,
Homagama
1 3 0771234567 75000/= 1
A0002 Namal de
Silva
Main Street,
Badulla
2 2 0711234567 65000/= 2
A0003 Nimali Peries New Town,
Embilipitiya
3 1 0781234567 78000/= 3
A0004 Kasun
Wijesinghe
New Town,
Ratnapura
3 1 0721234567 25000/= 4
A0005 Ridmi Perera Galle Road,
Moratuwa
1 2 0781234566 50000/= 3
A0006 Nalin Peries Jaffna Road,
Anuradhapura
4 NULL NULL 35000/= 5
Emp_details

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Dep_id dname
1 Finance
2 Sales
3 HR
4 Transport
department_details
id Dis_name
1 Colombo
2 Badulla
3 Ratnapura
4 Anuradhapura
dis_details
id De_name
1 Accountant
2 Group Leader
3 Manager
4 Trainee
5 Driver
desi_details
emp_no month value
A0001 January 75000/=
A0004 January 24150/=
A0005 February 48500/=
A0006 May 35000/=
Sal_payment

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1. List employees name and their designation (Use left join)
2. List employees name and their district (Use right join)
3. List employees name and their department (Use inner join)
4. List all employees full details
5. List the employees not included in the salary table

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Q & A

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Thank You!