This document introduces SQL (Structured Query Language), highlighting its role in managing relational databases and performing operations such as creating, updating, and extracting data. It covers selecting, filtering, and utilizing aggregate functions to analyze data, providing numerous examples and syntax for various operations. Additionally, it includes exercises for practicing SQL queries based on specified conditions.

1. SQL Introduction (Part 1)
Part 1

2. Database
Example:
- Personal Data
- customer transaction
- medical records
- etc
Stored
from
Multiple
Sources
Extracted
for
Multiple
Purposes
Form of
relational
tables

3. SQL (Structured Query Language)
Standardized programming language that's used to manage relational databases and
perform various operations on the data in them.
Operations example:
1. Create, Update, Delete -> mainly used by engineering
2. Extract and Wrangle -> mainly used by Analyst/Science
SQL Technology example:

4. Data engineer
Data Analyst/
Business Intelligence

5. Selecting Columns
SELECT column1, column2, …
FROM table_name;
Customers Table
Syntax
SELECT CustomerName, Address
FROM Customers;
Example 1
SELECT *
FROM Customers;
Example 2
source

6. Selecting Distinct
SELECT DISTINCT column1,
column2,
FROM table_name;
Customers Table
Syntax
SELECT DISTINCT Country
FROM Customers;
Example 1
source
SELECT DISTINCT Address
FROM Customers;
Example 2

7. WHERE Clause : To Filter Records
SELECT column1, column2, ...
FROM table_name
WHERE condition;
Customers Table
Syntax
SELECT * FROM Customers
WHERE Country= 'Mexico';
Example 1
source
SELECT * FROM Customers
WHERE CustomerID=1;
Example 2
*requires single/double quotes
around text values

8. WHERE other operators
Customers Table
Other Operator
SELECT * FROM Customers
WHERE CustomerName like 'D%';
Example 1
source
SELECT * FROM Customers
WHERE CustomerID>=88;
Example 2
= , >, <, >=, <=, <>/!=
Between, Like, In

9. WHERE AND, OR and NOT Operators
Syntax And
source
SELECT column1, column2,
FROM table_name
WHERE condition1 OR
condition2 OR condition3 ;
Syntax Or
The WHERE clause can be combined with AND, OR, and NOT operators.
The AND and OR operators are used to filter records based on more than one condition:
● The AND operator displays a record if all the conditions separated by AND are TRUE.
● The OR operator displays a record if any of the conditions separated by OR is TRUE.
The NOT operator displays a record if the condition(s) is NOT TRUE.
SELECT column1, column2,
FROM table_name
WHERE condition1 AND
condition2 AND condition3
SELECT column1, column2, ...
FROM table_name
WHERE NOT condition;
Syntax Not

10. WHERE AND, OR and NOT Operators: Example
Customer Table
SELECT * FROM Customers
WHERE Country='Germany' AND
(City='Berlin' OR City='München');
Example 1
source
SELECT * FROM Customers
WHERE Country Not in ('Germany','USA');
Example 2

11. Aggregate Functions: to summarize data
source
MIN() returns the smallest value of the selected column
MAX() returns the largest value of the selected column
COUNT() returns the number of rows that matches a specified criterion
AVG() returns the average value of a numeric column
SUM() returns the total sum of a numeric column
SELECT ‘Aggregate Funct’(column_name)
FROM table_name
WHERE condition;
Syntax

12. MIN() & MAX() + Alias
Products Table
SELECT MIN(Price) AS SmallestPrice
FROM Products;
Example 1
source
SELECT MAX(Price) AS LargestPrice
FROM Products;
Example 2

13. COUNT() & AVG() + Alias
Products Table
SELECT COUNT(ProductID) AS TotalProducts
FROM Products;
Example 1
source
SELECT AVG(Price) Average_Price
FROM Products;
Example 2

14. SUM() + Alias + Where
OrderDetails Table
SELECT SUM(Quantity) TotalQuantity
FROM OrderDetails;
Example 1
source
SELECT SUM(Quantity)TotalQuantity
FROM OrderDetails
WHERE ProductID in (11,14,51)
Example 2

15. Quiz Time!

16. Exercise 1
source
From the following table, write a SQL query to output CustomerName, Address, and City from Country USA
and Germany, except cities: München, Portland, Seattle.
Customer Table

17. Exercise 2
source
How many unique city from USA and Germany?
Customer Table

18. Exercise 3
source
From the following table, write a SQL query to output CustomerName, PostalCode . With customer’s name
ends with ‘a’ letter, and Postal Code start with 1 or 0
Customers Table

19. Exercise 4
source
From the following table, write a SQL query to output Average Price from SupplierID 10-20
Products Table

20. Exercise 5
source
From the following table, write a SQL query to output:
1. Total Unique Order id
2. Min, Max, Total, and Average Quantity
With criteria ProductID >50 or ProductID <10
OrderDetails Table

22. Source
https://searchdatamanagement.techtarget.com/definition/SQL
https://www.w3schools.com/sql/sql_select.asp