Database Management Fall 2003 The one-to-many relationship Joins, Views, Subqueries & Group by.

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Presentation transcript:

Database Management Fall 2003 The one-to-many relationship Joins, Views, Subqueries & Group by

stock stkcodestkfirmstkpricestkqtystkdivstkpe FCFreedonia Copper PTPatagonian Tea ARAbyssinian Ruby SLGSri Lankan Gold ILZIndian Lead &Zinc BEBurmese Elephant BSBolivian Sheep NGNigerian Geese CSCanadian Sugar ROFRoyal Ostrich Farms MGMinnesota Gold GPGeorgia Peach NENarembeen Emu QDQueensland Diamond IRIndooroopilly Ruby BDBombay Duck Add exchange rate information

stock stkcodestkfirmstkpricestkqtystkdivstkpenatnameexchrate FCFreedonia Copper United Kingdom1.00 PTPatagonian Tea United Kingdom1.00 ARAbyssinian Ruby United Kingdom1.00 SLGSri Lankan Gold United Kingdom1.00 ILZIndian Lead &Zinc United Kingdom1.00 BEBurmese Elephant United Kingdom1.00 BSBolivian Sheep United Kingdom1.00 NGNigerian Geese United Kingdom1.00 CSCanadian Sugar United Kingdom1.00 ROFRoyal Ostrich Farms United Kingdom1.00 MGMinnesota Gold USA0.67 GPGeorgia Peach USA0.67 NENarembeen Emu Australia0.46 QDQueensland Diamond Australia0.46 IRIndooroopilly Ruby Australia0.46 BDBombay Duck India

stock stkcodestkfirmstkpricestkqtystkdivstkpenatnameexchrate FCFreedonia Copper United Kingdom1.00 PTPatagonian Tea United Kingdom1.00 ARAbyssinian Ruby United Kingdom1.00 SLGSri Lankan Gold United Kingdom1.00 ILZIndian Lead &Zinc United Kingdom1.00 BEBurmese Elephant United Kingdom1.00 BSBolivian Sheep United Kingdom1.00 NGNigerian Geese United Kingdom1.00 CSCanadian Sugar United Kingdom1.00 ROFRoyal Ostrich Farms United Kingdom1.00 MGMinnesota Gold USA0.67 GPGeorgia Peach USA0.67 NENarembeen Emu Australia 0.51 QDQueensland Diamond Australia0.46 IRIndooroopilly Ruby Australia0.46 BDBombay Duck India Update Anomaly

stock stkcodestkfirmstkpricestkqtystkdivstkpenatnameexchrate FCFreedonia Copper United Kingdom1.00 PTPatagonian Tea United Kingdom1.00 ARAbyssinian Ruby United Kingdom1.00 SLGSri Lankan Gold United Kingdom1.00 ILZIndian Lead &Zinc United Kingdom1.00 BEBurmese Elephant United Kingdom1.00 BSBolivian Sheep United Kingdom1.00 NGNigerian Geese United Kingdom1.00 CSCanadian Sugar United Kingdom1.00 ROFRoyal Ostrich Farms United Kingdom1.00 Japan0.85 MGMinnesota Gold USA0.67 GPGeorgia Peach USA0.67 NENarembeen Emu Australia0.46 QDQueensland Diamond Australia0.46 IRIndooroopilly Ruby Australia0.46 BDBombay Duck India Insert Anomaly

stock stkcodestkfirmstkpricestkqtystkdivstkpenatnameexchrate FCFreedonia Copper United Kingdom1.00 PTPatagonian Tea United Kingdom1.00 ARAbyssinian Ruby United Kingdom1.00 SLGSri Lankan Gold United Kingdom1.00 ILZIndian Lead &Zinc United Kingdom1.00 BEBurmese Elephant United Kingdom1.00 BSBolivian Sheep United Kingdom1.00 NGNigerian Geese United Kingdom1.00 CSCanadian Sugar United Kingdom1.00 ROFRoyal Ostrich Farms United Kingdom1.00 MGMinnesota Gold USA0.67 GPGeorgia Peach USA0.67 NENarembeen Emu Australia0.46 QDQueensland Diamond Australia0.46 IRIndooroopilly Ruby Australia0.46 Delete Anomaly – India exchrate data lost

NATION and STOCK nation natcodenatnameexchrate UKUnited Kingdom1.00 USAUnited States0.67 AUSAustralia0.46 INDIndia stock stkcodestkfirmstkpricestkqtystkdivstkpenatcode FCFreedonia Copper UK PTPatagonian Tea UK ARAbyssinian Ruby UK SLGSri Lankan Gold UK ILZIndian Lead &Zinc UK BEBurmese Elephant UK BSBolivian Sheep UK NGNigerian Geese UK CSCanadian Sugar UK ROFRoyal Ostrich Farms UK MGMinnesota Gold USA GPGeorgia Peach USA NENarembeen Emu AUS QDQueensland Diamond AUS IRIndooroopilly Ruby AUS BDBombay Duck IND Foreign Key

nation natcodenatnameexchrate UKUnited Kingdom1.00 USAUnited States0.67 AUSAustralia 0.51 INDIndia stock stkcodestkfirmstkpricestkqtystkdivstkpenatcode FCFreedonia Copper UK PTPatagonian Tea UK ARAbyssinian Ruby UK SLGSri Lankan Gold UK ILZIndian Lead &Zinc UK BEBurmese Elephant UK BSBolivian Sheep UK NGNigerian Geese UK CSCanadian Sugar UK ROFRoyal Ostrich Farms UK MGMinnesota Gold USA GPGeorgia Peach USA NENarembeen Emu AUS QDQueensland Diamond AUS IRIndooroopilly Ruby AUS BDBombay Duck IND Update anomaly eliminated

nation natcodenatnameexchrate UKUnited Kingdom1.00 USAUnited States0.67 AUSAustralia0.46 INDIndia JPJapan0.85 stock stkcodestkfirmstkpricestkqtystkdivstkpenatcode FCFreedonia Copper UK PTPatagonian Tea UK ARAbyssinian Ruby UK SLGSri Lankan Gold UK ILZIndian Lead &Zinc UK BEBurmese Elephant UK BSBolivian Sheep UK NGNigerian Geese UK CSCanadian Sugar UK ROFRoyal Ostrich Farms UK MGMinnesota Gold USA GPGeorgia Peach USA NENarembeen Emu AUS QDQueensland Diamond AUS IRIndooroopilly Ruby AUS BDBombay Duck IND Insert anomaly eliminated

nation natcodenatnameexchrate UKUnited Kingdom1.00 USAUnited States0.67 AUSAustralia0.46 INDIndia stock stkcodestkfirmstkpricestkqtystkdivstkpenatcode FCFreedonia Copper UK PTPatagonian Tea UK ARAbyssinian Ruby UK SLGSri Lankan Gold UK ILZIndian Lead &Zinc UK BEBurmese Elephant UK BSBolivian Sheep UK NGNigerian Geese UK CSCanadian Sugar UK ROFRoyal Ostrich Farms UK MGMinnesota Gold USA GPGeorgia Peach USA NENarembeen Emu AUS QDQueensland Diamond AUS IRIndooroopilly Ruby AUS Delete anomaly eliminated

Data modeling – representing the 1:M relationship Watson’s looks like this: Ours will look like this:

Foreign keys A foreign key is a column that is a primary key of another table –natcode in stock is a foreign key because natcode is the primary key of nation Record a 1:m relationship the foreign key goes on the M side foreign key-primary key matching Names for a foreign key and the corresponding primary key are often the same, but not always

Referential integrity constraint For every value of a foreign key there is a primary key with that value For every value of natcode in stock there is a value of natcode in nation A foreign key can never be null A primary key must exist before the foreign key can be defined –Must create the nation before its stocks

Creating the tables CREATE TABLE nation ( natcodeCHAR(3), natnameVARCHAR(20), exchrateDECIMAL(9,5), PRIMARY KEY (natcode)); CREATE TABLE stock ( stkcodeCHAR(3), stkfirmVARCHAR(20), stkpriceDECIMAL(6,2), stkqtyDECIMAL(8), stkdivDECIMAL(5,2), stkpeDECIMAL(5), natcodeCHAR(3), PRIMARY KEY(stkcode), CONSTRAINT fk_stock_nation FOREIGN KEY(natcode) REFERENCES nation)

o Doing a join using WHERE with = (an equijoin) and qualification. o Using GROUP BY with one or more operations (e.g., COUNT, SUM) that produce a single result (results row) for each group. o Using HAVING (functionally similar to WHERE) to pick a subset of the groups identified by a GROUP BY. o Using a subquery (inner query, nested SELECT) to define a condition to evaluate in the WHERE clause of an outer query. Also – the correlated subquery. o Using CREATE VIEW to create a view or virtual table. Other basic SQL

stkcodestkfirmstkpricestkqtystkdivstkpenatcodenatcode1natnameexchrate NENarembeen Emu AUS Australia IRIndooroopilly Ruby AUS Australia QDQueensland Diamond AUS Australia BDBombay Duck IND India ROFRoyal Ostrich Farms UK United Kingdom CSCanadian Sugar UK United Kingdom FCFreedonia Copper UK United Kingdom BSBolivian Sheep UK United Kingdom BEBurmese Elephant UK United Kingdom ILZIndian Lead & Zinc UK United Kingdom SLGSri Lankan Gold UK United Kingdom ARAbyssinian Ruby UK United Kingdom PTPatagonian Tea UK United Kingdom NGNigerian Geese UK United Kingdom MGMinnesota Gold US United States GPGeorgia Peach US United States Join Create a new table from two existing tables by matching on a common column SELECT * FROM stock, nation WHERE stock.natcode = nation.natcode

Report the value of each stock holding in UK pounds. Sort the report by nation and firm. SELECT natname, stkfirm, stkprice, stkqty, exchrate, stkprice*stkqty*exchrate AS stkvalue FROM stock, nation WHERE stock.natcode = nation.natcode ORDER BY natname, stkfirm Join

natnamestkfirmstkpricestkqtyexchratestkvalue AustraliaIndooroopilly Ruby AustraliaNarembeen Emu AustraliaQueensland Diamond IndiaBombay Duck United KingdomAbyssinian Ruby United KingdomBolivian Sheep United KingdomBurmese Elephant United KingdomCanadian Sugar United KingdomFreedonia Copper United KingdomIndian Lead & Zinc United KingdomNigerian Geese United KingdomPatagonian Tea United KingdomRoyal Ostrich Farms United KingdomSri Lankan Gold United StatesGeorgia Peach United StatesMinnesota Gold

GROUP BY - reporting by groups Report by nation the total value of stockholdings. SELECT natname, SUM(stkprice*stkqty*exchrate) AS stkvalue FROM stock, nation WHERE stock.natcode = nation.natcode GROUP BY natname natnamestkvalue Australia India United Kingdom United States

HAVING - the WHERE clause of groups Report the total value of stocks for nations with two or more listed stocks. SELECT natname, SUM(stkprice*stkqty*exchrate) AS stkvalue FROM stock, nation WHERE stock.natcode = nation.natcode GROUP BY natname HAVING COUNT(*) >= 2; natnamestkvalue Australia United Kingdom United States

Subqueries A query nested within another query Report the names of all Australian stocks: SELECT stkfirm FROM stock WHERE natcode IN (SELECT natcode FROM nation WHERE natname = 'Australia') stkfirm Narembeen Emu Queensland Diamond Indooroopilly Ruby

Correlated subquery Solves the inner query many times Find those stocks where the quantity is greater than the average for that country: SELECT natname, stkfirm, stkqty FROM stock, nation WHERE stock.natcode = nation.natcode AND stkqty > (SELECT AVG(stkqty) FROM stock WHERE stock.natcode = nation.natcode) natnamestkfirmstkqty AustraliaQueensland Diamond89251 United KingdomBolivian Sheep United KingdomRoyal Ostrich Farms United StatesMinnesota Gold816122

Views - virtual tables An imaginary table constructed by the DBMS when required Only the definition of the view is stored, not the result CREATE VIEW stkvalue (nation, firm, price, qty, exchrate, value) AS SELECT natname, stkfirm, stkprice, stkqty, exchrate, stkprice*stkqty*exchrate FROM stock, nation WHERE stock.natcode = nation.natcode

Views - querying Query exactly as if a table SELECT nation, firm FROM stkvalue WHERE value > nationfirm AustraliaNarembeen Emu AustraliaIndooroopilly Ruby AustraliaQueensland Diamond United KingdomRoyal Ostrich Farms United KingdomCanadian Sugar United KingdomFreedonia Copper United KingdomBolivian Sheep United KingdomIndian Lead & Zinc United KingdomSri Lankan Gold United KingdomAbyssinian Ruby United KingdomPatagonian Tea United KingdomNigerian Geese United StatesMinnesota Gold United StatesGeorgia Peach

Key ideas (… so to speak) o the foreign key goes on the M side othe foreign key doesn’t go on the 1 side (this would create a multi-valued attribute – bad) o foreign key-primary key matching o names for a foreign key and the corresponding primary key are often the same, but not always oreferential integrity constraint: … when a record (row) on the M side references a record on the 1 side, the latter must exist! This implies that the 1-side record must be added first; it also implies that it cannot be deleted as long as any record on the M side references it. Implementing the 1:M relationship in the actual database …