sql kho tài liệu training

LEARN SQL AND PHP
INTRODUCTION TO SQL


WHAT IS SQL ?!
• Structural Query Language is a language to
manage and
• To manage data inside database
• By manage we mean:
•
•
•
•
•
•
•

Selecting;
Deleting;
Updating;
Adding;
Creating on-demand Functions;
Views;
Procedures.


WHAT IS DATABASES
• A database is a collection of information that is
organized so that it can easily be accessed,
managed, and updated.

WHAT IS DATABASES
• FOOD
•
•
•
•
•

FISH
MEAT
VEGETABLES
FRUITS
…


WHAT IS DATABASES
RELATIONAL + DATABASES


DATA TYPE OF A DATABASE
• A database can contain multiple types of data:
• VARCHAR(n): characters where n is a number of characters
that admin chose;
• INT: integers;
• BLOB: for binary data fields(like images, files, maps,…);
• LONGBLOB: for long binary files;
• DATETIME: date and time field as: YYYY-MM-DD HH:mm:ss;
• DATE: for dates only as YYYY-MM-DD;
• TIME : for time fields;

• YEAR, DECIMAL, TIMESTAMP,…


CREATE DATABASE
• Regrouping multiple tables that hold a connected
information into one environment, represent a
database.
• Syntax: to create a database test_db
CREATE SCHEMA IF NOT EXISTS `test_db`;
USE `test_db` ;


CREATE A TABLE
• To create a table inside a database, let us assume
that we have a table called test_db that contains 2
columns (id and name) where id is primary key:
CREATE TABLE IF NOT EXISTS `test_db`.`test_tbl` ( `id`
INT NOT NULL, `name` VARCHAR(20) NOT NULL,
PRIMARY KEY (`id `))

• NOT NULL represent a mandatory field to be filled
by admins or users.


SELECT QUERY
• Select query consist of selecting all or specific rows
or columns of a table when a condition is true;
• It provide GROUP BY and ORDER BY functionality;
• Syntax:
DATA

QUERY

All data

SELECT * FROM tbl_name;

Specific columns

SELECT id, name, address FROM
tbl_name;

Specific rows

SELECT * FROM tbl_name WHERE
id_column >10;


SELECT QUERY
• GROUP BY:
• If sometimes, a specific user in a table has multiple rows of
data, we can regroup all of his rows into 1.
• Syntax:
SELECT * FROM tbl_name GROUP BY column_name;

• ORDER BY:
• To order data by ascending ASC or descending DESC;
• So if we want to re-order the table by placing
name_column from A to Z we can use the following query:
SELECT * FROM tbl_name GROUP BY column_name

ORDER BY column_name ASC;


SELECT QUERY
• LIMIT 1:
• If a user has multiple rows in a table and we want to select
at most 1 row for him we add LIMIT 1 clause to the query;
• Syntax:

SELECT * FROM tbl_name WHERE column_name = ‘X’
LIMIT 1;


INSERT QUERY
• Insert query help us to add more rows into a table;
• Syntax:
INSERT INTO tbl_name (name, address,
phone_number) VALUES (‘X’, ‘DC’, ‘1234567890’);

• If the primary key (usually an ID column) of the table
is not Auto-Increment, we should add id to the
query.
INSERT INTO tbl_name (id, name, address,
phone_number) VALUES (23, ‘X’, ‘DC’, ‘1234567890’);


UPDATE QUERY
• If we have a table called test_tbl and contain id as
primary key, name, and address, and we need to
update a row where an id=29 to new values:

• Syntax:
UPDATE test_tbl SET name=‘new name’, address =
‘new address’ WHERE id =29;


FOREIGN KEYS
• A foreign key in a table is a primary key of another;
• If we have the following table:
• Tbl_address
id

Name

Address

1

X

DC

2

Y

NY

3

Z

LA

• Tbl_phone
Another_id

id

Phone_number

5436

1

123456

5453

2

534535

5478

3

324227


FOREIGN KEY

• So, the id of the first table is a foreign key into the
other;
• To create a table with a foreign Key:
CREATE TABLE IF NOT EXIST tbl_phone (
new_id INT NOT NULL AUTO INCREMENT,
phone_number VARCHAR(18) NOT NULL,
PRIMARY KEY (new_id),
FOREIGN KEY (id) REFERENCES tbl_address);


JOINS
• To select multiple rows from different tables we use
JOIN;
• There is various types of JOINS but the most used is
INNER JOIN;
• Syntax:
SELECT tbl_phone.id, tbl_phone.phone_number,
tbl_address.name FROM tbl_phone INNER JOIN
tbl_address WHERE tbl_phone.id = tbl_phone.id


JOINS
• The result of the previous query is:
id

address

Phone_number

1

X

123456

2

Y

534535

3

Z

324227


FUNCTIONS – AVG
• AVG(): to calculate the average of a column when
a certain condition is true;
• Syntax:

SELECT avg(tbl_name.age_column) FROM tbl_name
WHERE age_column > 18;


FUNCTIONS – COUNT()
• TO count number of rows in a table;
• Syntax:

SELECT COUNT(id) FROM tbl_name;

• Or:
SELECT COUNT(id) FROM tbl_name WHERE id <18;


FUNCTIONS – MAX, MIN, SUM
•
•
•
•

MAX() to return the maximum value of a column;
MIN() to return the minimum value of a column;
SUM() to return the sum of a column;
Syntax:
Function

Query

MIN()

SELECT MIN(salary) FROM
tbl_name

MAX()

SELECT MAX(salary) FROM
tbl_name

SUM

SELECT SUM(salary) FROM
tbl_name


TABLES AND RELATIONS
• Primary Keys vs Foreign Keys
Id

Name

Address

12

John

WDC

13

Peter

NY

14

Sarah

LA

Id

Emp_id

Social Number

5426

12

56569

5427

13

23654

5428

14

71254


TABLES AND RELATIONS
• Primary Keys vs Foreign Keys

Id

Name

Address

12

John

WDC

13

Peter

NY

14

Sarah

LA

1:1
Id

Emp_id

Social Number

5426

12

56569

5427

13

23654

5428

14

71254


TABLES AND RELATIONS
• Primary Keys vs Foreign Keys
Id

Name

12

John

13

Peter

14

Sarah
1:N

Id

Emp_id

Project

5426

12

CIVIL

5427

13

ELECTRIC

5428

14

ELECTRONIC


TABLES AND RELATIONS
• Primary Keys vs Foreign Keys
Id

Name

12

John

13

Peter

14

Sarah
M:N

Id

Emp_id

Project

5426

12

MANAGER

5427

12

MANAGER

5428

14

IT SPECIALIST