Structured Query Language (SQL) Advanced Topics And How to build something useful

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Structured Query Language (SQL)Advanced Topics

And

How to build something useful

MIS 304 Winter 2006

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Goal for this class

• Advanced SQL Commands• Understand how to use Relational

Technologies to solve “M to N” and other advanced problems.

• Understand Relational Database Cost/Benefit analysis.

• Be able to write SQL queries to solve advanced problems.

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Advanced SQL

• SQL is at the same time simple and yet deceptively complex.

• Worse, simple queries can run very slowly and complex one very quickly.

• The trick to learning SQL is just to do it.

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Sub Queries

• Anything enclosed in Parentheses ( ) is done first as a separate query.

• It returns a result set that you can use in the “main” query.

• Commonly used with the IN operator.

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IN

• SELECT * FROM Product WHERE V_Code = 12345 OR V_Code = 12346;

• SELECT * FROM Product WHERE V_Code IN (12345, 12346);

• SELECT * FROM Product WHERE V_Code IN (SELECT V_CODE FROM VENDOR WHERE State = ‘MI’);

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Sub Query Hints

• Sub Queries can be hard to use.• Develop the Sub Query first as a

separate query. Make sure it works independently first.

• Remember a Sub Query returns a ‘virtual’ table.

• Keep sub queries to a minimum.

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• Listing Unique Values

SELECT DISTINCT P_CODEFROM POLine;

SELECT DISTINCT SELECT DISTINCT

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SELECT TOP*

SELECT TOP n FROM nnn WHERE x=y

Example:SELECT TOP 5 TotalPopFROM CountyORDER BY TotalPop DESC;

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LIKE

• Show all of the data for Products whose Description contains CD (i.e. CD, CD-ROM, CD-RW…)

• SELECT * FROM ProductWHERE Description LIKE ‘CD%’;

• % Multicharacter match (* in Access)• _ Single character match (? In Access)

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6Soundex

There is an “algorithm” that lets you search for words that sound alike.

1. Capitalize all letters in the word and drop all punctuation marks. Pad the word with rightmost blanks as needed during each procedure step.

2. Retain the first letter of the word. 3. Change all occurrence of the following letters to '0' (zero):

'A', E', 'I', 'O', 'U', 'H', 'W', 'Y'. 4. Change letters from the following sets into the digit given:

– 1 = 'B', 'F', 'P', 'V' – 2 = 'C', 'G', 'J', 'K', 'Q', 'S', 'X', 'Z' – 3 = 'D','T' – 4 = 'L' – 5 = 'M','N' – 6 = 'R'

5. Remove all pairs of digits which occur beside each other from the string that resulted after step (4).

6. Remove all zeros from the string that results from step 5.0 (placed there in step 3)

7. Pad the string that resulted from step (6) with trailing zeros and return only the first four positions, which will be of the form <uppercase letter> <digit> <digit> <digit>.

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6Converting Columns to Rows

• Suppose you have a table that has Attributes for the various months and you now need to roll to another year.

• SELECT Code, Jan FROM TestUNION ALL SELECT Code, Feb FROM TestUNION ALL SELECT Code, Mar FROM TestUNION ALL SELECT Code, Apr FROM Test;

Code Jan Feb Mar Apr …

1 20 23 24 25

2 33 56 67 55

3 21 22 22 22

Test

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ExampleCOLA COLB COLC COLD 1 2 3 4 5 6 7 8

ResultCOLX COLY A 1 A 5 B 2 B 6 C 3 C 7 D 4 D 8

SELECT 'A' as COLX, COLA as COLY from Example UNION ALL SELECT 'B' , COLB from Example UNION ALL SELECT 'C' , COLC from Example UNION ALLSELECT 'D' , COLDfrom Example order by COLX, COLY

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How to Build Something Useful

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The Issue

• Businesses, Health Care facilities, Non-profits, the Military and Governmental agencies run on the movement of information. In other words…

Paperwork

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The Business of IT

• Very often you are given a bunch of seemingly unconnected “artifacts” and you need to make something out of them.

• These can take the form of Databases, Files, Spreadsheets, Word Documents but most often pieces of paper.

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Paperwork

• Modeling the structure and the flow of paper or now paper like objects is the nature of what IT people do.

• Most of those pieces of paper end up as one or more tables in a relational database.

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Forms Examples

• The Purchase Order• The Invoice• Intake logs• Test results• Etc…..

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Forms and Business Rules

• Forms also encode many of our business rules

• You may need to represent some of the business rules in your database.

• Examples– Code sets

– Numbering schemes

– etc

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What is so difficult about this?

• What are the “Facts” we find here?

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Facts about many things

• Facts about the PO or Invoice itself• Facts about customers or suppliers• Facts about items sold or shipped• Facts about payment• Facts about shipping• Facts about business process• Misc. facts

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Lets build a model

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The Simplest VersionPhase 0

PurchaseOrder

What is wrong with this approach?

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PO Table

What are these facts about?

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POInfo Lines

M1

PO Model phase 1PO Model phase 1

Has

How much redundancy does this add?

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Results

• You need a new Foreign Key in the Lines table that adds a link to the new Primary Key PONumber

• This means you are going to duplicate the PONumber many times in the tables.

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What else can we do?

• Look for other “redundancies”• What is the Cost/Benefit of adding new

tables to address them?1

New FK FieldSize X N = %ofDuplicates X Total RecordSize X N

New FK FieldSize = %ofDuplicates Total RecordSize

1. cost of redundancy only

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POInfo Line

N1

Vendor

1


Has

Has

M

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POInfo Product

PONumber LineKey

1 M

PartNum

PONumber

M 1

PartNum

Vendor

VendNum

VendNum

POLine

M


PartDescr

VendAddr

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Where do you put?

• Totals and subtotals?

• Taxes?

• Payment details?

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Data Dictionary

Table Attribute DataType PK/FK On

Vendor V_Code Integer PK

V_Name Char

Product P_Code Integer PK

POInfo PONum Integer PK

V_Code Integer FK Vendor

POLine LineKey Integer PK

PONum Integer FK POInfo

P_Code Integer FK Product

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Now Build the Tables

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Data Definition CommandsData Definition Commands

CREATE TABLE POInfo (PO_Number FCHAR(5) NOT NULL

UNIQUE,V_CODE FCHAR(3) NOT NULL,PRIMARY KEY (PO_Number);

FOREIGN KEY (S_CODE) REFERENCES VENDOR ON DELETE RESTRICT

ON UPDATE CASCADE));

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CREATE TABLE POLine(LineKey FCHAR(5) NOT NULL UNIQUE, PONumber VCHAR(35) NOT NULL, PartNum VCHAR(15) NOT NULL, PRIMARY KEY (LineKey));

FOREIGN KEY (PONumber) REFERENCES POInfo ON DELETE RESTRICT


FOREIGN KEY (PartNum) REFERENCES Product ON DELETE RESTRICT


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CREATE TABLE Vendor(V_CODE FCHAR(5) NOT NULL UNIQUE, V_NAME VCHAR(35) NOT NULL, V_CONTACT VCHAR(15)NOT NULL, V_AREACODE FCHAR(3) NOT NULL, V_PHONE FCHAR(3) NOT NULL, V_STATE FCHAR(2) NOT NULL, v_ORDER FCHAR(1) NOT NULL, PRIMARY KEY (V_CODE));

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CREATE TABLE PRODUCT(P_CODE VCHAR(10) NOT NULL UNIQUE, P_DESCRIPT VCHAR(35) NOT NULL, P_INDATE DATE NOT NULL, P_ONHAND SMALLINT NOT NULL, P_MIN SMALLINT NOT NULL, P_PRICE DECIMAL(8,2) NOT NULL, P_DISCOUNT DECIMAL(4,1) NOT NULL, V_CODE SMALLINT, PRIMARY KEY (P_CODE), FOREIGN KEY (S_CODE) REFERENCES VENDOR ON DELETE RESTRICT

ON UPDATE CASCADE);

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• SQL Integrity Constraints

– Entity Integrity• PRIMARY KEY• NOT NULL and UNIQUE

– Referential Integrity• FOREIGN KEY • ON DELETE• ON UPDATE

Remember the business rules!

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How About “Payment Type”?

• How do you handle something like this?• What is it a “fact” about.

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How about a more Complex Example

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Sub Sections

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Modeling Issues

• Keep the “Facts” right.• Look at the Cost/Benefit relationships• Make sure you get rid of all of the

M x N relationships.• KISS = Keep It Simple Students.

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So now that you built it

• We need to query it.• We need to manage it.

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How would we recreate the Purchase Order in SQL?

• It depends on what the Model looks like.

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Phase 0 revisited

Simple SQL based on One table.

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Listing the Table ContentsListing the Table Contents

SELECT * FROM PurchaseOrder;

SELECT P_CODE, P_DESCRIPT, P_INDATE, P_ONHAND, P_MIN, P-PRICE, P_DISCOUNT, S_CODE FROM PurchaseOrder;

But we said this One Table approach was too costly!

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POInfo Parts

PONumber LineKey

1 M

PartNum

PONumber

M 1

PartNum

Vendor

VendNum

VendNum

POLine

M

PO Model phase 3PO Model phase 3PartDescr

VendAddr

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The Key Question

• What do you want to know?

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Bringing it Together

• We now need to get information from more than one table.

• This is done with the SQL “Join”.• Joins use the Primary and Foreign

Keys to link the tables in the SQL Command together.

Remember!!!WHERE TABLE1.PRIMARY=TABLE2.FOREIGN

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More Complex Queries

SELECT PRODUCT.P_DESCRIPT, PRODUCT.P_PRICE, VENDOR.V_NAME, VENDOR.V_CONTACT, VENDOR.V_AREACODE, VENDOR.V_PHONEFROM PRODUCT, VENDORWHERE PRODUCT.V_CODE = VENDOR.V_CODE

AND VENDOR.V_CODE=1234;

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Another Cost

• When you join two tables you incur a cost due to the Join process.

• A Join builds an intermediate file that this the combination of all of the entity instances of the one table combined with all of the entity instances of the other table.

• These tables can get very large.

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Join

WHERE CUSTOMER.AGENT_CODE = AGENT.AGENT_CODE

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Product of the two tables

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Refine the Join

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More Complex Queries

• Anything in a valid SQL statement can be put in the WHERE part of a joined SQL Query.

• More than two tables can be joined.• YOU MUST HAVE THE JOIN EQUALITY• This means they can get quite complex• You can use Sub Queries ( ) and

“pretty printing” to help keep things straight.

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Print a PO

SELECT PO.PONumber, VENDOR.V_NAME, POLine.Line, PRODUCT.P_CODE, PRODUCT.P_DESCRIPT, PRODUCT.P_PRICE

FROM VENDOR, PRODUCT, PO, POLine WHERE PO.PONumber = POLine.PONumber

AND PRODUCT.P_CODE = POLine.P_CODE AND VENDOR.V_CODE = PO.V_CODE

AND PO.PONumber ="1001";

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Results

PONumber V_NAME Line P_CODE P_DESCRIPT P_PRICE

1001 Rubicon Sis.

1 11QER/31 Power painter, 15 psi., 3-nozzle

$109.99

1001 Rubicon Sis.

2 WR3/TT3 Steel matting, 4'x8'x1/6", .5" mesh

$119.95

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Complications

• Any “high fidelity” representation of the PO is going to take multiple passes through the SQL engine.

• The best way to do this is with a Report Writing tool. (e.g. Crystal Reports)

• Even the report tool is SQL based.

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Sub Query Example

SELECT PRODUCT.P_DESCRIPT, PRODUCT.P_PRICE, VENDOR.V_NAME

FROM PRODUCT, VENDORWHERE PRODUCT.V_CODE =

VENDOR.V_CODEAND VENDOR.V_CODE IN

(SELECT VENDOR.V_CODE FROM VENDOR WHERE VENDOR.V_CODE > “1234-TK”) ;

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Data Input

• What can we learn about Data Input from looking at the models?

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Data Input

• The more complex the model the more data validation issues you have.

• Here again you can use a sub query to look up data in an existing table.

• You also need to SQL Enable data input devices.

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