Databases (MariaDB/MySQL) CS401, Fall 2015

Transcription

1 Databases (MariaDB/MySQL) CS401, Fall 2015

2 Database Basics Relational Database Method of structuring data as tables associated to each other by shared attributes. Tables (kind of like a Java class) have rows (records or tuples) (kind of like an object) columns (attributes or fields of records) (kind of like an instance variable)

3 Database Basics Use Structured Query Language (SQL) to define, manage, and search data. Why do we use them? Fast compared to files. Scale well for large data sets. Built-in failure recovery. Concurrency (multi-user) features.

4 Database Software Oracle Microsoft SQL Server PostgreSQL MySQL/MariaDB We will use MariaDB in this course. Basically the same as MySQL.

5 Example Database

6 Website Concept Imagine we have an online discussion board with a diverse user group. When a user signs up, they will provide a username, password, address, name, age, and species. Users can leave posts. We want to keep track of who posts what.

7 users id username password first_name last_name age gender 123 snoopy snoopypass com Snoopy Brown 7 M 222 blackwidow nataliapass natalia@example.com Natalia Romanova 30 F 223 mulan mulanpass mulan@example.com Mulan Hua 18 F species users_species posts id species user_id species_id id user_id message posted 2276 human Woof woof! :23: dog 2278 rabbit This is better, but for simplicity in our example, we don t do this. Why is it better than having it in users? I ll never make my father happy :( :18: woof woof woof!! :22:19

8 Setting up your database on WebDev SSH to onyx, then SSH to webdev. Login to MariaDB. mysql -u yourlogin -p You can change your password if you wish. set password for localhost = PASSWORD( sup3rs3cr3t ); Specify which database you want to use use yourlogin;

9 Running Your First Query To see your current set of tables, run show tables; You have no tables, so this should return empty set (0.0 sec)

10 SQL Basics

11 SQL Basics

12 Creating a table CREATE TABLE name ( columnname type constraints, columnname type constraints ); DROP TABLE name; DROP TABLE IF EXISTS name;

13 Creating a table DROP TABLE IF EXISTS users; CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, username VARCHAR(50) NOT NULL UNIQUE, VARCHAR(100) NOT NULL, password VARCHAR(128) NOT NULL, first_name VARCHAR(50) NOT NULL, last_name VARCHAR(50) NOT NULL, age INT NOT NULL );

14 Types (most common)

15 Column Constraints

16 Let s do it. Create the table as shown in create_tables. sql Follow tutorial as shown in sql_tutorial.sql Show and describe tables after creating. SHOW TABLES; DESCRIBE users;

17 Inspecting the database. Show and describe tables after creating. SHOW DATABASES; SHOW TABLES; DESCRIBE table;

18 INSERTing data. INSERT INTO table VALUES(value1, value2,...); INSERT INTO table(col1, col2,...) VALUES(value1, value2,...);

19 SELECTing data. SELECT column(s) FROM table; SELECT * FROM table; SELECT col1, col2 FROM table;

20 SELECTing DISTINCT data. DISTINCT SELECT DISTINCT column(s) FROM table; SELECT DISTINCT gender FROM users;

21 Filtering data using WHERE clause WHERE SELECT column(s) FROM table WHERE condition(s); WHERE SELECT = > >= < <= <> BETWEEN min AND max

22 Multiple WHERE clauses: AND/OR AND OR SELECT column(s) FROM table WHERE condition AND condition;

23 Wildcard Matching: LIKE / REGEX SELECT column(s) FROM table WHERE column LIKE pattern; SELECT column(s) FROM table WHERE column REGEX expression;

24 Ordering Output: ORDER BY SELECT column(s) FROM table WHERE column LIKE pattern ORDER BY column; ORDER BY column DESC;

25 Limiting Output: LIMIT SELECT column(s) FROM table WHERE column LIKE pattern ORDER BY column LIMIT n;

26 Aggregate Data: AVG / COUNT SELECT AVG(column) FROM table; SELECT COUNT(*) FROM table;

27 UPDATEing Rows UPDATE table SET column_name = value, column_name = value WHERE condition(s);

28 DELETEing Rows DELETE FROM table WHERE condition(s); DELETE FROM table; -- Will delete ALL rows.

29 Multi-table Queries: JOIN JOIN ON SELECT JOIN WHERE ON FROM

30 Multi-table Queries: JOIN SELECT FROM JOIN ON users posts id username password snoopy snoopypass id user_id message posted Woof woof! :23: blackwidow nataliapass I ll never make my father happy :( :18: mulan mulanpass mulan@example.com woof woof woof!! :22:19

31 SELECT FROM Multi-table JOIN Queries: ON JOIN users posts id username password snoopy snoopypass id user_id message posted Woof woof! :23: blackwidow nataliapass I ll never make my father happy :( :18: mulan mulanpass mulan@example.com woof woof woof!! :22:19 users JOIN posts username message snoopy Woof woof! mulan I ll never make my father happy :( snoopy woof woof woof!!