Relational DBs and SQL

Designing Your Web Database (Ch. 8)→Creating and Working with a MySQL Database (Ch. 9, 10)

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Relational DBs and SQL

Topics:Relational database concepts and terminologyDesigning your web databaseWeb database architecture – three-tier web applicationsSQL → MySQL, command line

Creating tables Inserting data into the database Updating records from the database Deleting records from the database Retrieving data from the database Dropping tables

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A RDBMS exposes to the user:A collection of independent tables

A set of relationships between the tables

A powerful and flexible 4GL, called the SQL language (Structured Query Language), for managing and querying data in tables.

The Relational Model

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The database schema for the Book-O-Rama database we use in chapters 9 and 10:

Customers (CustomerID, Name, Address, City)

Orders (OrderID, CustomerID, Amount, Date)

Books (ISBN, Author, Title, Price)

Order_Items (OrderID, ISBN, Quantity) → composite PK, 2 FKs to Orders and Books!

Book_Reviews (ISBN, Reviews) → a PK which is also a FK!

The Relational Model

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After designing the relational DB, you need a RDBMS to implement, populate, and query your database → we use MySQLInstalled on cscdb.nku.edu server

The MySQL DBMS: Can support many different databases → usually there is one

database per application

Each one of you has a database called db_yourusername (ex db_campana1)

Can have many users, each has an account & password → usually at least one user per web application

Each one of you has an account yourusername (ex campana1) with same password as for FTP access

MySQL

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The MySQL DBMS: Supports a sophisticated privilege system.

Privilege = the right to perform a particular action on a particular db object (table, index etc) and is associated with (aka granted to) a particular user.

Principle of least privilege = a user should have the lowest level of privilege required to perform his assigned task.

Each one of you has been granted: The privilege to connect to the MySQL server running on cscdb.nku.edu

The privileges to create/drop tables and execute insert/delete/update/select commands on tables in your own database only!

MySQL

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A command line client, for setting up tables …Find client mysql.exe at http://www.nku.edu/~frank/csc301/Handouts/mysql.zip.

→ download, set up path environment variableConnect from a command line interface (= command window) →

mysql –h cscdb.nku.edu –u yourusername –p →

password will be automatically requested →Go to your database with command use db_yourusername; →You can issue now SQL commands to create tables, manipulate and query

data → all commands should end with “;” !

Web script connections – later!

MySQL – Connect and Log In

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Structured Query Language = the “programming language” for relational databasesSQL is a nonprocedural language = the user specifies what

must be done (ex. create a table), but not how it is to be done.SQL Standards: SQL-99 or SQL3 → portabilitySeveral SQL dialects exist, in different RDBMSs; minor

differences among them.

SQL

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SQL is a command language; its functions fit into two broad categories:Data definition language (DDL) → commands to:

Create database objects, such as tables, indexes, and views Define access rights to database objects

Data manipulation language (DML) → commands to insert, update, delete, and retrieve data within database tables

At the heart of SQL is the concept of a query = any SQL command (statement) that must be executed; can be:a question that must be answered an action to be executed (e.g. adding or deleting table rows).

SQL

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Use CREATE TABLE command for each db table, basic syntax:

CREATE TABLE tablename (column_1 data_type [constraints] [,column_2 data_type [constraints],…column_k data_type [constraints] ] [,PRIMARY KEY (column_i [, column_j …]) ]

);

Notes:End each SQL command with a semicolon to execute it;A comma separates all table element (column, PK) definitions;[…] indicates an optional parameter / part of the statement

SQL – Creating DB Tables

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Constraints:not null = all the rows in the table must have a value in that

column

→ all primary key columns should be not null; are automatically.auto_increment = if column set to null or no value provided for it

when inserting a new row, MySQL sets it to (last value generated for column | max value) + 1

→ can be used for at most one integer column in a table (usually for the PK)

primary keyunsigned = only values 0 allowed → for an integer type only

SQL – Creating DB Tables

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Example:

CREATE TABLE CUSTOMERS (customer_id int unsigned not null auto_increment primary key,name char(50) not null,address char(100) not null,city char(30) not null

);A SQL script with all Book-O-Rama db table definitions:

http://www.nku.edu/~frank/csc301/Examples/MySQL/bookorama.sql

To run a SQL command file sql_cmd_file.sql:

mysql –h host –u username –D database –p < sql_cmd_file.sql

SQL – Creating DB Tables

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Most identifiers have a 64-character length limit Identifiers for:

Databases – databases in MySQL map to directories in the underlying OS file structure

Tables – tables in MySQL map to files in the underlying file structure case-sensitivity for database and table names is same as OS’s

names & chars allowed: those allowed for directory/file names in OSColumns, indexes, aliases

identifiers are case insensitive, but different cases not allowed in the same SQL query

most ASCII chars allowed, but recommended to use letters and “normal” & meaningful names

MySQL Identifiers

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MySQL Identifiers – cont.

Do not use the /, \, . characters in database and table namesAvoid using mathematical symbols in column names, such

as +, - CUSTOMER-ID error!

Avoid using SQL reserved words as column names;Reserved words = words used by SQL to perform specific

functions; for example, CREATE.

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Numeric types

Type Options Description

INT UNSIGNED An integer between +/- 2 billion or 0 to 4 billion if UNSIGNED

ZEROFILL adds zeros on left to pad to full field width

TINYINT -same- -127.. 128 or 0..255 if UNSIGNED

  FLOAT (precision) Floating point nr. Precision: 4 or 8 (# bytes)

FLOAT(width, #decimals) Same as FLOAT(4) with specified display width and # of decimal places

DOUBLE(width, #decimals) Same as FLOAT(8) with specified display width and # of decimal places

MySQL – Common Column Data Types

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Date and Time typesType DescriptionDATE Date in format YYYY-MM-DDDATETIME Date and time in format YYYY-MM-DD HH:MM:SS

String typesType Options DescriptionCHAR (maxl) BINARY A string 'maxl' characters long; fixed length. maxl: 0 to 255 Default is case-insensitive; BINARY makes

the field case-sensitive.

VARCHAR(maxl) BINARY A string 'maxl' characters long; variable length.

TEXT A text block up to 65535 characters long.

ENUM('val1','val2','val3‘ ...) A string column that can only have values from the specified list or NULL.

MySQL – Common Column Data Types

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After you create the tables in your database, you can view:All tables in the currently used database

with:

show tables;

The structure of any of the tables in the

current database with:

describe table_name;

MySQL - SHOW and DESCRIBE

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Use DROP TABLE command for each db table you want to delete; basic syntax:

DROP TABLE tablename;

Note:This command deletes all the rows in the table tablename and the

table tablename itself!

SQL – Deleting DB Tables

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