structured query language stat 598 w lecture 27. outline introduction to sql & mysql single...
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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', '[email protected]'),
('Website', 'www.stat.purdue.edu/~wang913'),
('Address', 'Purdue University'),
('Phone', '765-714-4263');
+--------------+-------------+---------------------------------+
| ID | TYPE | DETAILS |
+--------------+-------------+---------------------------------+
| 1 | Email | [email protected] |
| 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)