MySQL Quick Guide

ISYS 475

Working with MySQL

• MySQL executable is stoted in this folder:– c:\xampp\mysql\bin

Managing MySQL using phpMyAdmin

• Start XAMPP control panel• Click MySQL Admin button• This will open the phpMyAdmin with the default

browser. FireFox works better than IE.

phpMyAdmin Windows

Create a New MySQL Database: HRDB

• Add a new table: EmployeeTable– EID Char 10 *** Under Index, select

Primary– Ename VARChar 30– Sex Char 1– Salary Decimal and enter 10,2 for value– HireDate Date

• Enter data:– Click the Insert button.

To Create a New Database• 1. Click the Home button of phpMyAdmin• 2. Click the Databases button• 3. Enter a new database name and click Create

Add A New Table in the New Database

• 1. Click the Home button• 2. Select the database• 3.Click the Create Table button

Enter Data

• Click the Insert button.

• Enter data

• Click GO button

To View Data

• Click SQL button

• Enter a query

• Click GO

MySQL Command Line

• To get Windows command prompt:– Start/Enter cmd

• Change directory to:– C:\xampp\mysql\bin– C:\Users\David>cd c:\xampp\mysql\bin

• Enter command:– c:\xampp\mysql\bin>mysql -u root -p

Creating and Use a Database

• CREATE DATABASE mydb;

• USE mydb

Show

• SHOW DATABASES– Show all databases

• SHOW TABLES– List all tables in the default database

• SHOW COLUMNS FROM tableName– List all columns in a given table.

Editing SQL Commands

• MySQL stores the most recent commands. We can edit the command as follow:– Use the Up, Down arrow key to select and

correct the command, then press Enter.

Creating Command Files• Use a text editor to create a file with SQL

commands and save it with extension .txt• To run the command file:

– SOURCE commandFileName.txt• Ex: mysql> source c:\MySQLCommand.txt

mysql> source c:\teaching\475\ProcShowCustomers.txt;Outfile disabled.ERROR:Unknown command '\4'.ERROR:Unknown command '\P'.ERROR:Failed to open file 'c:eaching\475\ProcShowCustomers.txt', error: 2mysql> Source C:/teaching/475/ProcShowCustomers.txt;Query OK, 0 rows affected, 1 warning (0.01 sec)

Query OK, 0 rows affected (0.01 sec)

Note: Use the “/” for Windows

Example of a command file

Drop table IF EXISTS customers;Create table customers (cid char(3), cname varchar(20),city varchar(20), rating char(1));Insert into customers values('C1', 'MYERS','CHICAGO','A');Insert into customers values('C2', 'GOODMAN','SAN FRANCISCO','B');Insert into customers values('C3', 'LEE','CHICAGO','A');Insert into customers values('C4', 'GRAUER','LOS ANGELES','C');

User-Defined Variables

• User variables are written as @var_name.

mysql> SET @t1=1, @t2=2, @t3:=4;mysql> SELECT @t1, @t2, @t3, @t4 := @t1+@t2+@t3;+------+------+------+--------------------+| @t1 | @t2 | @t3 | @t4 := @t1+@t2+@t3 |+------+------+------+--------------------+| 1 | 2 | 4 | 7 | +------+------+------+--------------------+

Create a New Database from a command file using PHPMyAdmin

• 1. Click the Home button and click the Databases button; enter a new database name and click Create.

• 2. Click the Import button and the Browse button to select the command file.

Basic Query Language Operations

• Selection

• Projection

• Join

• Aggregates: Max, Min, Sum, Avg, Count– Totals and SubTotals– GroupBy

• Having

• Calculated fields

Selection

• Selection operation retrieves records that satisfy user’s criteria.

• Criteria: >, >=, <, <=, =, <>

: Range: odate between '2006-01-01' and '2007-01-01‘

Projection

SELECT fields FROM tableName WHERE criteria;

To eliminate duplication:• SELECT DISTINCT fields FROM tableName WHERE

criteria;

• Field name alias: AS• Ex: select cid as CustomerID, cname as customerName from

customers;

Natural Join• SELECT * FROM table1 NATURAL JOIN table2;

– SELECT * FROM customers NATURAL JOIN orders;

• SELECT * FROM table1, table2 WHERE table1.JoinAttribute = table2.JoinAttribute;– SELECT * FROM customers, orders – WHERE customers.cid = orders.cid;

• Table name alias:– SELECT * FROM customers c, orders o

• WHERE c.cid = o.cid;

• Other forms:– FROM customers c JOIN orders o ON c.cid=o.cid;– FROM customers c INNER JOIN orders o ON c.cid=o.cid;

Aggregates

• SELECT AVG(fieldName) FROM tableName;– COUNT(fieldName), COUNT(*)– COUNT(DISTINCT fieldName)– MAX(fieldName)– MIN(fieldName)– SUM(fieldName)

• More than one aggregate:• SELECT AVG(fieldName), MAX(fieldName),

MIN(fieldName) FROM tableName;• With alias:

– SELECT COUNT(cid) AS NumberOfCustomer FROM customers;

GROUP BY• SELECT groupingFields, function(fieldname) FROM tablename GROUP

BY groupingFields;– SELECT cIty, count(cid) FROM customers GROUP BY city;– SELECT city, rating, count(cid) FROM customers GROUP BY city, rating;

• Compute subtotals from a join Compute the number of courses taken by each student:– SELECT cid, cname, COUNT(oid)

• FROM customers NATURAL JOIN orders• GROUP BY cid;

• Note 1: WHERE clause must come before the GROUP BY:– SELECT major, count(sid) FROM student WHERE GPA > 3.0 GROUP BY

major;

Adding a Criteria for the Sub Totals with HAVING

• SELECT city, count(cid) FROM customers– GROUP BY city– HAVING count(cid) > 5;

• Sometime the aggregates are not required to display:– Find majors that have more than 5 students:– SELECT city FROM customers

• GROUP BY city• HAVING count(cid) > 5;

Calculated Fields

• Define a calculated field:– (salary*.15) as Tax– (Year(Now()) – Year(DOB)) AS Age– IF function

Calculated Field Examples

• Using functions:– Select oid, cid, year(odate) as OrderYear from

orders;

• Using expression:– select pid, pname,sum(qty*price) as

TotalSales from products natural join odetails group by pid;

• Using IF function:– SELECT pid, pname, if( price >500, 'Expensive', ‘Not

expensive' ) FROM products;

SQL Insert CommandINSERT INTO tableName VALUES (field values separated by commas);

INSERT INTO tableName (Column names separated by commas)VALUES (field values separated by commas);

Ex 1. Customer table with CID, CNAME, CITY, RATING.

a. INSERT INTO CUSTOMER VALUES (‘C1’, ‘SMITH’, ‘SF’, ‘A’);

b. INSERT INTO CUSTOMER (CID, CNAME,RATING) VALUES (‘C1’, ‘SMITH’, ‘A’);

SQL Delete Command

DELETE FROM tableName [WHERE criteria];

Ex 1. Delete a record from the Customer table.

DELETE FROM CUSTOMER WHERE CID = ‘C1’;

SQL Update Command

UPDATE tableName SET field = new value [WHERE criteria];

Ex 1.

UPDATE CUSTOMER SET RATING = ‘A’ WHERE CID=‘C1’;

Ex 2.

UPDATE CUSTOMER SET CITY = ‘SF’, RATING = ‘A’ WHERE CID=‘C1’;

Practice: University Database ERD

Student Account

Faculty Course

Has1 1

EnrollM MAdvise

M

1

SIDSname Major SID Balance

FID Fname CID CnameUnitsPhone

Grade

GPA

Use SQL Statements to Answer

• Q1: Display students’ ID, name and account balance who owe university more than $2000.

• Q2: Display student’s ID, name and total units.

• Q3: Find students taking at least 9 units and display their ID, Name and total units.

• Q4: Display CID, Cname, SID, Sname• Q5: Display CID, Cname, number of

students in each course.• Q6: Display faculty’s name and phone if the

faculty advises at least three students.