Structured Query Language

Structured Query Language

STAT 598 W

Lecture 27

Outline

Introduction to SQL & MySQL

Single table Queries

– Using computed columns

– Using special operators: LIKE, IN, BETWEEN

– Columns with NULL values

– Sorting data

– Using group functions

– The GROUP BY clause

Structured Query Language (SQL)

Mid-1970s:– SQL was developed at IBM under the name SEQUEL

1980:– Renamed as SQL to avoid confusion with an unrelated

hardware product called SEQUEL

Most relational DBMSes use some version of SQL

SQL (cont.)

Is an English-like language

Communicates with an SQL Server

Manipulates data and table definitions in the

database

Supports operations of Relational Algebra

SQL Statements Data Retrieval

SELECT

Data Definition Language (DDL) CREATE, ALTER, DROP, RENAME, TRUNCATE

Data Manipulation Language (DML) INSERT, UPDATE, DELETE

Data Control Language (DCL) GRANT, REVOKE

Transaction control COMMIT, ROLLBACK, SAVEPOINT

SQL Statements (cont.)

SQL statements are free format

SQL statements can be placed on one or more lines

Statements are entered in SQL Buffer

Keywords cannot be abbreviated or split across lines

Clauses are usually placed one per line

Indentations are used to improve readability

Functions are utilized to perform data manipulation as well

as formatting output of a query

The end of a statement is indicated by a semicolon

MySQL Database Universe

MySQL Administrator MySQL Workbench

mysqldmin mysql mysqldump

MySQL Clients and Tools

mysqld MySQL Server

MySQL APIs

Connector/Net

Connector/ODBCConnector/J

GUI Tools

Command Line Tools

Connector/PHP Connector/C Connector/C++

MySQL Command Line Tools

mysql

mysqld Server Process

mysqladmin

mysqldump

SELECTUPDATE. . .BACKUPRESTORECHECK. . .

SHUTDOWN

BACKUP

DB

Essential mysql Commands

mysql> SHOW databases; to show available databases

mysql> CREATE DATABASE premiere; to create new database

mysql> USE premiere; to start using Premiere database

mysql> SHOW tables; to show available tables in default db

mysql> SOURCE c:\premiere.txt to run a script file

mysql> DESCRIBE customer; to show structure of customer table

mysql> EXIT to exit the mysql client

Help in MySQL Type “help” at mysql> prompt, or

Type “help” followed by name of a statemente.g.:– help select– help union

Also available:– Reference Manual: on-line or pdf version

mysql> help

For information about MySQL products and services, visit: http://www.mysql.com/For developer information, including the MySQL Reference Manual, visit: http://dev.mysql.com/To buy MySQL Enterprise support, training, or other products, visit: https://shop.mysql.com/

List of all MySQL commands:Note that all text commands must be first on line and end with ';'? (\?) Synonym for 'help'.clear (\c) Clear the current input statement.connect (\r) Reconnect to the server. Optional arguments are db and host.delimiter (\d) Set statement delimiter.ego (\G) Send command to mysql server, display result vertically.exit (\q) Exit mysql. Same as quit.go (\g) Send command to mysql server.help (\h) Display this help.notee (\t) Don't write into outfile.print (\p) Print current command.prompt (\R) Change your mysql prompt.quit (\q) Quit mysql.rehash (\#) Rebuild completion hash.source (\.) Execute an SQL script file. Takes a file name as an argument.status (\s) Get status information from the server.tee (\T) Set outfile [to_outfile]. Append everything into given outfile.use (\u) Use another database. Takes database name as argument.charset (\C) Switch to another charset. Might be needed for processing binlog

with multi-byte charsets.warnings (\W) Show warnings after every statement.nowarning (\w) Don't show warnings after every statement.

SQL Editor SQL server is built in most computers, but in

some cases only administrator has full access to it. In order to practice your SQL editing skills, you

may download some “SQL Editor” online for free. To make it even simpler, you can directly use

some kind of SQL online-editor, such as “SQL Fiddle”.

Create a simple table

CREATE TABLE Contacts

(

id int auto_increment primary key,

type varchar(20),

details varchar(80)

);

INSERT INTO Contacts

(type, details)

VALUES

('Email', 'wang913@purdue.edu'),

('Website', 'www.stat.purdue.edu/~wang913'),

('Address', 'Purdue University'),

('Phone', '765-714-4263');

+--------------+-------------+---------------------------------+

| ID | TYPE | DETAILS |

+--------------+-------------+---------------------------------+

| 1 | Email | wang913@purdue.edu |

| 2 | Website | www.stat.purdue.edu/~wang913 |

| 3 | Address | Purdue University |

| 4 | Phone | 765-714-4263 |

+--------------+----------------------------+------------------+

Insert from a data file

BULK INSERT MyTable FROM 'c:\data.csv'

WITH

(

FIELDTERMINATOR = ',',

ROWTERMINATOR = '\n'

)

Use “BULK INSERT”:

Premiere Products Model

REP (Rep_num, Last_Name, First_Name, Street, City, State, Zip, Commission, Rate)

CUSTOMER (Customer_num, Customer_Name, Street, City, State, Zip, Balance,

Credit_limit, Rep_num*)

ORDER (Order_num, Order_date, Customer_num*)

ORDER_LINE (Order_num*, Part_num*, Num_ordered, Quoted_price)

PART (Part_num, Description, Warehouse, Class, Price, On_hand)

places(1, 1)

(1, N)

represents(1, 1) (1, N)

CUSTOMER

ORDERhasORDER_LINEincluded inPART(1, N) (1, 1)(0, N)(1, 1)

REP

Source: “A Guide to MySQL” by Philip J. Pratt and Mary Z. Last , Course Technology, 2006

Existing Tables in a Default DB To find out what tables exist in the default

database, use the SHOW command:

mysql> show tables;+--------------------+| Tables_in_premiere |+--------------------+| customer || order_line || orders || part || rep |+--------------------+5 rows in set (0.00 sec)

Displaying a Table Structure

The DESCRIBE command:

mysql> desc customer;+---------------+--------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+---------------+--------------+------+-----+---------+-------+| CUSTOMER_NUM | char(3) | NO | PRI | NULL | || CUSTOMER_NAME | char(35) | NO | | NULL | || STREET | char(15) | YES | | NULL | || CITY | char(15) | YES | | NULL | || STATE | char(2) | YES | | NULL | || ZIP | char(5) | YES | | NULL | || BALANCE | decimal(8,2) | YES | | NULL | || CREDIT_LIMIT | decimal(8,2) | YES | | NULL | || REP_NUM | char(2) | YES | | NULL | |+---------------+--------------+------+-----+---------+-------+9 rows in set (0.01 sec)

SELECT Statement

SELECT column(s)

FROM table(s)

WHERE row condition

GROUP BY column(s)

HAVING group condition

ORDER BY column(s)

LIMIT m, n;

WHERE Clause Find the number, name, balance, and credit limit

for each customer with balance that exceeds the credit limit.

mysql> SELECT customer_num,customer_name, balance, credit_limit -> FROM customer -> WHERE balance > credit_limit;+--------------+---------------------+---------+--------------+| customer_num | customer_name | balance | credit_limit |+--------------+---------------------+---------+--------------+| 408 | The Everything Shop | 5285.25 | 5000.00 || 842 | All Season | 8221.00 | 7500.00 |+--------------+---------------------+---------+--------------+2 rows in set (0.02 sec)

Compound Condition List the description of every part that is not in

warehouse number 3 and that has more than 20 units on hand.

mysql> SELECT description -> FROM part -> WHERE warehouse <> '3' -> AND on_hand > 20;+----------------+| description |+----------------+| Home Gym || Microwave Oven |+----------------+2 rows in set (0.05 sec)

Expressions Find the number, name, and available credit for

each customer with at least $5,000 of available credit.

mysql> SELECT customer_num, customer_name, -> (credit_limit - balance) as "Available Credit" -> FROM customer -> WHERE (credit_limit - balance) >= 5000;+--------------+----------------------------+------------------+| customer_num | customer_name | Available Credit |+--------------+----------------------------+------------------+| 282 | Brookings Direct | 9568.50 || 462 | Bargains Galore | 6588.00 || 608 | Johnson's Department Store | 7894.00 || 725 | Deerfield's Four Seasons | 7252.00 |+--------------+----------------------------+------------------+4 rows in set (0.00 sec)

BETWEEN operator BETWEEN operator makes certain SELECT statements

simpler

List customer number, name, and balance for customers with their balance between $2,000 and $5,000.

mysql> SELECT customer_num, customer_name, balance -> FROM customer -> WHERE balance BETWEEN 2000 AND 5000;+--------------+----------------------------+---------+| customer_num | customer_name | balance |+--------------+----------------------------+---------+| 462 | Bargains Galore | 3412.00 || 608 | Johnson's Department Store | 2106.00 || 687 | Lee's Sport and Appliance | 2851.00 |+--------------+----------------------------+---------+3 rows in set (0.00 sec)

LIKE operator LIKE operator is used when exact character type

matches are not applicable

LIKE is used with wildcard searches

% (percent) – matches any string of zero or more characters

_ (underscore) – matches any individual character

The ESCAPE option can be used to define escape character symbol

LIKE operator (cont.) List customer number, name, and complete address

of each customer with a street name that contains “Central”.

mysql> SELECT customer_num, customer_name, street, city, state, zip -> FROM customer -> WHERE street LIKE '%Central%';+--------------+-----------------+--------------+-------+-------+-------+| customer_num | customer_name | street | city | state | zip |+--------------+-----------------+--------------+-------+-------+-------+| 462 | Bargains Galore | 3829 Central | Grove | FL | 33321 |+--------------+-----------------+--------------+-------+-------+-------+1 row in set (0.00 sec)

LIKE operator (cont.) You have a difficulty reading a report because someone spilled

coffee on it. You can only tell the first digit (‘4’) of the customer# and the last digit (‘8’). The second digit is hard to read. Can you find the customer name and complete address?

mysql> SELECT customer_num, customer_name, street, city, state, zip -> FROM customer -> WHERE customer_num LIKE '4_8';+--------------+---------------------+------------+---------+-------+-------+| customer_num | customer_name | street | city | state | zip |+--------------+---------------------+------------+---------+-------+-------+| 408 | The Everything Shop | 1828 Raven | Crystal | FL | 33503 |+--------------+---------------------+------------+---------+-------+-------+1 row in set (0.03 sec)

IN operator The IN operator provides a concise way to test for

values in a specified set.

List the customer number, name, and credit limit for each customer with a credit limit of $5,000, $10,000, or $15,000.mysql> SELECT customer_num, customer_name, credit_limit -> FROM customer -> WHERE credit_limit IN (5000, 10000, 15000);+--------------+----------------------------+--------------+| customer_num | customer_name | credit_limit |+--------------+----------------------------+--------------+| 282 | Brookings Direct | 10000.00 || 408 | The Everything Shop | 5000.00 || 462 | Bargains Galore | 10000.00 || 524 | Kline's | 15000.00 || 608 | Johnson's Department Store | 10000.00 || 687 | Lee's Sport and Appliance | 5000.00 |+--------------+----------------------------+--------------+6 rows in set (0.00 sec)

Null Values Occasionally, when you enter a new row into a

table or modify an existing row, the values for one or more columns are unknown or unavailablee.g., A sales representative is not assigned to a customer

This special value is called a null data value, or null. The null is not the same as zero or blank space.

Three Valued Logic Any comparison with null returns unknown value

e.g.15 > null, null = null, column < null,

column = null

Result of WHERE clause predicate is treated as false if it evaluates to unknown

Three Valued Logic (cont.)

AND TRUE FALSE UNKNOWNTRUE TRUE FALSE UNKNOWNFALSE FALSE FALSE FALSE

UNKNOWN UNKNOWN FALSE UNKNOWN

OR TRUE FALSE UNKNOWNTRUE TRUE TRUE TRUEFALSE TRUE FALSE UNKNOWN

UNKNOWN TRUE UNKNOWN UNKNOWN

NOT(not unknown) evaluates to unknown

Selecting rows with NULL values Do we have a complete address for each customer?

List the number and name of each customer with an unknown/missing street information.

mysql> SELECT customer_num, customer_name -> FROM customer -> WHERE street IS NULL;Empty set (0.00 sec)

Rules of Precedence The rules determine the order in which expressions

are evaluated

The default order:1. Parenthesis2. Arithmetic operators3. Comparison conditions, IS, LIKE, IN4. BETWEEN, CASE5. NOT logical condition6. AND logical condition7. OR logical condition

This order can be modified by using parentheses

Sorting Typically rows are displayed in the order in which

they were inserted The ORDER BY clause can be used to list data in a

desired order The column(s) on which data is to be sorted is

called a sort key(s)– The sort keys are listed in the order of importance

To sort in descending order use the DESC operator (default is ASC)

Sorting List the customer number, name, and balance of

each customer. Order the output in ascending (increasing) order of balance.

mysql> SELECT customer_num, customer_name, balance -> FROM customer -> ORDER BY balance -> LIMIT 5;+--------------+----------------------------+----------+| customer_num | customer_name | balance |+--------------+----------------------------+----------+| 725 | Deerfield's Four Seasons | 248.00 || 282 | Brookings Direct | 431.50 || 608 | Johnson's Department Store | 2106.00 || 687 | Lee's Sport and Appliance | 2851.00 || 462 | Bargains Galore | 3412.00 |+--------------+----------------------------+----------+5 rows in set (0.00 sec)

Sorting with multiple keys List the customer number, name, and credit limit

of every customer, ordered by credit limit in descending order and by name within credit limit.

mysql> SELECT customer_num, customer_name cname, credit_limit -> FROM customer -> ORDER BY credit_limit DESC, cname -> LIMIT 5;+--------------+----------------------------+--------------+| customer_num | cname | credit_limit |+--------------+----------------------------+--------------+| 524 | Kline's | 15000.00 || 462 | Bargains Galore | 10000.00 || 282 | Brookings Direct | 10000.00 || 608 | Johnson's Department Store | 10000.00 || 148 | Al's Appliance and Sport | 7500.00 |+--------------+----------------------------+--------------+5 rows in set (0.00 sec)

Group Functions

SUM – Sum of values in a column

AVG – Average value in a column

COUNT – Number of values in a column

MAX – Maximum value in a column

MIN – Minimum value in a column

STDDEV – Standard Deviation of values in a column

VARIANCE – Variance of values in a column

Group Functions (cont.)

They operate on a set of values as input and give

one value as a result

COUNT, MAX and MIN functions can be used with

any data type

SUM, AVG, STDDEV, and VARIANCE can be used

only with numeric data types

All group functions ignore null values except

COUNT(*)

Counting rows in a table

How many parts are in item class HW?

mysql> SELECT COUNT(*) -> FROM part -> WHERE class = 'HW';+----------+| COUNT(*) |+----------+| 3 |+----------+1 row in set (0.00 sec)

SUM function Find the total number of customers and the total

of their balances.

mysql> SELECT COUNT(*) "Number of Customers", -> SUM(balance) "Total Balance" -> FROM customer;+---------------------+---------------+| Number of Customers | Total Balance |+---------------------+---------------+| 10 | 47651.75 |+---------------------+---------------+1 row in set (0.00 sec)

Summary statistics Provide summary statistics of customer balance.

mysql> SELECT COUNT(balance) N, AVG(balance) Xbar,

-> MIN(balance) Min, MAX(balance) Max,

-> STD(balance) S

-> FROM customer;

+----+-------------+--------+----------+-------------+

| N | Xbar | Min | Max | S |

+----+-------------+--------+----------+-------------+

| 10 | 4765.175000 | 248.00 | 12762.00 | 3635.106972 |

+----+-------------+--------+----------+-------------+

1 row in set (0.00 sec)

MIN function with character type Alphabetically, what is the first and the last part

description in the PART Table.

mysql> SELECT MIN(description) First, -> MAX(description) Last -> FROM part;+----------------+--------+| First | Last |+----------------+--------+| Cordless Drill | Washer | +----------------+--------+1 row in set (0.00 sec)

DISTINCT operator

To avoid duplicates, either when listing or

counting values, precede the column name with

the DISTINCT operator

DISTINCT operator is not a function

Useful when used within COUNT function

Results with repeated rows Find the customer number of each customer that

currently has an open order (i.e., an order in the ORDERS table).

mysql> SELECT customer_num -> FROM orders;+--------------+| customer_num |+--------------+| 148 || 356 || 408 || 282 || 608 || 148 || 608 |+--------------+7 rows in set (0.03 sec)

Results without repeated rows Find the customer number of each customer that

currently has an open order. List each customer only once.

mysql> SELECT DISTINCT customer_num -> FROM orders;+--------------+| customer_num |+--------------+| 148 || 356 || 408 || 282 || 608 |+--------------+5 rows in set (0.00 sec)

DISTINCT used with COUNT Count the number of customers who currently

have open orders.

mysql> SELECT COUNT(customer_num) -> FROM orders;+---------------------+| COUNT(customer_num) |+---------------------+| 7 |+---------------------+1 row in set (0.00 sec)

mysql> SELECT COUNT(DISTINCT customer_num) -> FROM orders;+------------------------------+| COUNT(DISTINCT customer_num) |+------------------------------+| 5 |+------------------------------+1 row in set (0.00 sec)

Describing Groups of Data

SELECT column(s), ...

group_function(column)

FROM table(s)

WHERE row condition

GROUP BY column(s)

HAVING group condition

ORDER BY column(s)

LIMIT m, n;

Using the GROUP BY clause

GROUP BY clause allows rows that share some

common characteristics to be grouped Multiple columns and expressions can be used for

grouping Specified group functions are performed on each

group Columns in the GROUP BY clause do not have to

be in the SELECT list

Grouping Data

List class ID and the average unit price of products in each class.

mysql> SELECT class, AVG(price) -> FROM part -> GROUP BY class;+-------+-------------+| class | AVG(price) |+-------+-------------+| AP | 400.988000 || HW | 104.950000 || SG | 1092.475000 |+-------+-------------+3 rows in set (0.00 sec)

How does it work?

Part_Num Description On_hand Class Warehouse PriceAT94 Iron 50 HW 3 24.95BV06 Home Gym 45 SG 2 794.95CD52 Microwave Oven 32 AP 1 165.00DL71 Cordless Drill 21 HW 3 129.95DR93 Gas Range 8 AP 2 495.00DW11 Washer 12 AP 3 399.99FD21 Stand Mixer 22 HW 3 159.95KL62 Dryer 12 AP 1 349.95KT03 Dishwasher 8 AP 3 595.00KV29 Treadmill 9 SG 2 1390.00

Original PART table:

How does it work?

PART table sorted by “class”:

Part_Num Description On_hand Class Warehouse PriceCD52 Microwave Oven 32 AP 1 165.00DR93 Gas Range 8 AP 2 495.00DW11 Washer 12 AP 3 399.99KL62 Dryer 12 AP 1 349.95KT03 Dishwasher 8 AP 3 595.00AT94 Iron 50 HW 3 24.95DL71 Cordless Drill 21 HW 3 129.95FD21 Stand Mixer 22 HW 3 159.95BV06 Home Gym 45 SG 2 794.95KV29 Treadmill 9 SG 2 1390.00

We have 5 rows in AP class, 3 rows in HW class, 2 rows in SG class

AVR =400.99

AVR =1092.48

AVR =104.95

Do use group functions with GROUP BY

List class and average unit price in each class.

mysql> SELECT class, price -> FROM part -> GROUP BY class;+-------+--------+| class | price |+-------+--------+| AP | 165.00 || HW | 24.95 || SG | 794.95 |+-------+--------+3 rows in set (0.00 sec)

Grouping with GROUP_CONCAT()

The GROUP_CONCAT() function returns a string result with the concatenated values from a group

mysql> SELECT class, -> GROUP_CONCAT(DISTINCT description) List -> FROM part -> GROUP BY class;+-------+--------------------------------------------------+| class | List |+-------+--------------------------------------------------+| AP | Washer,Dishwasher,Microwave Oven,Dryer,Gas Range || HW | Stand Mixer,Iron,Cordless Drill || SG | Home Gym,Treadmill |+-------+--------------------------------------------------+3 rows in set (0.00 sec)

Grouping with GROUP_CONCAT()

mysql> SELECT class, -> GROUP_CONCAT(DISTINCT description) List -> FROM part -> GROUP BY class \G*************************** 1. row ***************************class: AP List: Washer,Dishwasher,Microwave Oven,Dryer,Gas Range*************************** 2. row ***************************class: HW List: Stand Mixer,Iron,Cordless Drill*************************** 3. row ***************************class: SG List: Home Gym,Treadmill3 rows in set (0.00 sec)

Using WITH ROLLUP clause For each warehouse and class, provide the average price

of part. Also provide the average price in each warehouse.

mysql> SELECT warehouse, class, AVG(price) -> FROM part -> GROUP BY warehouse, class -> WITH ROLLUP;+-----------+-------+-------------+| warehouse | class | AVG(price) |+-----------+-------+-------------+| 1 | AP | 257.475000 || 1 | NULL | 257.475000 || 2 | AP | 495.000000 || 2 | SG | 1092.475000 || 2 | NULL | 893.316667 || 3 | AP | 497.495000 || 3 | HW | 104.950000 || 3 | NULL | 261.968000 || NULL | NULL | 450.474000 |+-----------+-------+-------------+9 rows in set (0.00 sec)

Counting the rows in a group List each credit limit and the number of customers

having each credit limit.

mysql> SELECT credit_limit, COUNT(*) -> FROM customer -> GROUP BY credit_limit;+--------------+----------+| credit_limit | COUNT(*) |+--------------+----------+| 5000.00 | 2 || 7500.00 | 4 || 10000.00 | 3 || 15000.00 | 1 |+--------------+----------+4 rows in set (0.00 sec)

Using a HAVING clause List the order number and the total value for

orders over $1,000.

mysql> SELECT order_num, -> SUM(num_ordered*quoted_price) total -> FROM order_line -> GROUP BY order_num -> HAVING SUM(num_ordered*quoted_price) > 1000;+-----------+---------+| order_num | total |+-----------+---------+| 21613 | 1319.80 || 21614 | 1190.00 || 21617 | 2189.90 || 21623 | 2580.00 |+-----------+---------+4 rows in set (0.00 sec)

Displaying specific groups List each credit limit and the number of customers

having each credit limit held by more than one customer.

mysql> SELECT credit_limit, COUNT(*) -> FROM customer -> GROUP BY credit_limit -> HAVING COUNT(*) > 1;+--------------+----------+| credit_limit | COUNT(*) |+--------------+----------+| 5000.00 | 2 || 7500.00 | 4 || 10000.00 | 3 |+--------------+----------+3 rows in set (0.00 sec)

HAVING vs. WHERE

WHERE clause limits/restricts individual rows

HAVING clause limits/restricts output to certain

groups on the basis of aggregate information

Restricting the rows to be grouped List each credit limit and the number of customers

of sales rep 20 that have this credit limit.

mysql> SELECT credit_limit, COUNT(*) -> FROM customer -> WHERE rep_num = '20' -> GROUP BY credit_limit;+--------------+----------+| credit_limit | COUNT(*) |+--------------+----------+| 7500.00 | 2 || 15000.00 | 1 |+--------------+----------+2 rows in set (0.00 sec)

Restricting the rows and the groups Repeat previous example, but list only those credit

limits held by more than one customer.

mysql> SELECT CREDIT_LIMIT, COUNT(*) -> FROM CUSTOMER -> WHERE REP_NUM = '20' -> GROUP BY CREDIT_LIMIT -> HAVING COUNT(*) > 1;+--------------+----------+| CREDIT_LIMIT | COUNT(*) |+--------------+----------+| 7500.00 | 2 |+--------------+----------+1 row in set (0.00 sec)