DATABASE DESIGN I - 1DL300

Transcription

1 DATABASE DESIGN I - DL300 Fll 00 An introductory course on dtse systems Mnivskn Sesn Uppsl Dtse Lortory Deprtment of Informtion Technology, Uppsl University, Uppsl, Sweden 00--

2 Introduction to Reltionl Alger Elmsri/Nvthe ch 6 Pdron-McCrthy/Risch ch 0 Mnivskn Sesn Deprtment of Informtion Technology Uppsl University, Uppsl, Sweden 00--

3 Query lnguges Lnguges where users cn express wht informtion to retrieve from the dtse. Ctegories of query lnguges: Procedurl Non-procedurl (declrtive) Forml ( pure ) lnguges: Reltionl lger Reltionl clculus Tuple-reltionl clculus Domin-reltionl clculus Forml lnguges form underlying sis of query lnguges tht people use

4 Reltionl lger Reltionl lger is procedurl lnguge Opertions in reltionl lger tkes two or more reltions s rguments nd return new reltion. Reltionl lgeric opertions: Opertions from set theory: Union, Intersection, Difference, Crtesin product Opertions specificlly introduced for the reltionl dt model: Select, Project, Join It hve een shown tht the select, project, union, difference, nd Crtesin product opertions form complete set. Tht is ny other reltionl lger opertion cn e expressed in these

5 Opertions from set theory Reltions re required to e union comptile to e le to tke prt in the union, intersection nd difference opertions. Two reltions R nd R is sid to e union-comptile if: R D D... D n nd R D D... D n i.e. if they hve the sme degree nd the sme domins. 00--

6 Union opertion The union of two union-comptile reltions R nd S is the set of ll tuples tht either occur in R, S, or in oth. Nottion: R S Defined s: R S = {t t R or t S} For exmple: R S A B U A B 3 = A B

7 Difference opertion The difference etween two union-comptile sets R nd S is the set of ll tuples tht occur in R ut not in S. Nottion: R S Defined s: R S = {t t R nd t S} For exmple: R S A B A B 3 = A B

8 Intersection The intersection of two union-comptile sets R nd S, is the set of ll tuples tht occur in oth R nd S. Nottion: R S Defined s: R S = {t t R nd t S} For exmple: R S A B A B 3 = A B

9 Crtesin product Let R nd S e reltions with k nd k rities resp. The Crtesin product of R nd S is the set of ll possile k +k tuples where the first k components constitute tuple in R nd the lst k components tuple in S. Nottion: R S Defined s: R S = {t q t R nd q S} Assume tht ttriutes of r(r) nd s(s) re disjoint. (i.e. R ) S = ). If ttriutes of r(r) nd s(s) re not disjoint, then renming must e used. X =

10 Crtesin product exmple A B C D c 6 = A B C D c c c c 6

11 Selection opertion The selection opertor, σ, selects specific set of tuples from reltion ccording to selection condition (or selection predicte) P. Nottion: σ P (R) Defined s: σ P (R) = {t t R nd P(t) } (i.e. the set of tuples t in R tht fulfills the condition P) Where P is logicl expression (*) consisting of terms connected y: (nd), (or), (not) nd ech term is one of: <ttriute> op <ttriute> or <constnt>, where op is one of: =,, >,, <, Exmple: σ SALARY>30000 (EMPLOYEE) (*) formul in propositionl clculus 00--

12 Selection exmple = A B C D R σ A=B D > (R) = A B C D 4 7 9

13 Projection opertion The projection opertor, Π, picks out (or projects) listed columns from reltion nd cretes new reltion consisting of these columns. Nottion: Π A,A,...,Ak (R), where A, A R is reltion nme. The result is new reltion of k columns. re ttriute nmes nd Duplicte rows removed from result, since reltions re sets. Exmple: Π LNAME,FNAME,SALARY (EMPLOYEE)

14 Projection exmple = A B 3 4 C R Π A,C (R) = A C = A C

15 Join opertor The join opertor, (lmost, correct ), cretes new reltion y joining relted tuples from two reltions. Nottion: R C S C is the join condition which hs the form A r θ A s, where θ is one of {=, <, >,,, }. Severl terms cn e connected s C C...C k. A join opertion with this kind of generl join condition is clled Thet join. 00--

16 Exmple Thet join θ A F = A B C D 3 A B C 3 D E 3 F 4 R θ A F S E 3 F 4 R S

17 Equijoin The sme s join ut it is required tht ttriute A r nd ttriute A s should hve the sme vlue. Nottion: R C S C is the join condition which hs the form A r = A s. Severl terms cn e connected s C C...C k

18 Exmple Equijoin R S R B=C S A B C D E B=C = A B d 4 4 d 9 d e e e C D d 4 4 d E e e

19 Nturl join Nturl join is equivlent with the ppliction of join to R nd S with the equlity condition A r = A s (i.e. n equijoin) nd then removing the redundnt column A s in the result. Nottion: R * Ar,As S A r,a s re ttriute pirs tht should fulfill the join condition which hs the form A r = A s. Severl terms cn e connected s C C...C k

20 Exmple Nturl join R S R B=C S A B C D E B=C = A B d 4 4 d 9 d e e e D d 4 d E e e

21 Composition of opertions Expressions cn e uilt y composing multiple opertions Exmple: σ A=C (R S) A B C D = A B C D R S = 00-- σ A=C (R S) = c 6 c c 6 6 A B C D 6

22 Assignment opertion The ssignment opertion ( ) mkes it possile to ssign the result of n expression to temporry reltion vrile. Exmple: temp σ dno = (EMPLOYEE) result fnme,lnme,slry (temp) The result to the right of the is ssigned to the reltion vrile on the left of the. The vrile my e used in susequent expressions. 00--

23 Renming reltions nd ttriute The ssignment opertion cn lso e used to renme reltions nd ttriutes. Exmple: NEWEMP σ dno = (EMPLOYEE) R(FIRSTNAME,LASTNAME,SALARY) fnme,lnme,slry (NEWEMP)

24 Division opertion Suited to queries tht include the phrse for ll. Let R nd S e reltions on schems R nd S respectively, where R = (A,...,A m,b,...,b n ) S = (B,...,B n ) The result of R S is reltion on the schem R - S = (A,...,A m ) R S = {t t Π R-S (R) u S tu R}

25 Exmple of Division opertion = A e A B 3 B R S R S 00-- c d d d d e e

26 Additionl reltionl opertions Outer join nd outer union (presented together with SQL) Aggregtion opertions (presented together with SQL) Updte opertions (presented together with SQL) (not prt of pure query lnguge)

27 Aggregtion opertions Presented together with SQL lter Exmples of ggregtion opertions vg min mx sum count

28 Updte opertions Presented together with SQL lter Opertions for dtse updtes re normlly prt of the DML insert (of new tuples) updte (of ttriute vlues) delete (of tuples) Cn e expressed y mens of the ssignment opertor

29 Outer join/union opertion Extensions of the join/union opertions tht void loss of informtion. Computes the join/union nd then dds tuples from one reltion tht do not mtch tuples in the other reltion to the result of the join. Fills out with null vlues: null signifies tht the vlue is unknown or does not exist. All comprisons involving null re flse y definition

30 Exmple Outer join Reltion lon rnch-nme Downtown Redwood Perryridge lon-numer -70 L-30 L-60 mount Reltion orrower customer-nme Jones Smith Hyes lon-numer -70 L-30 L

31 Exmple Outer join cont... lon orrower (nturl join) rnch-nme lon-numer mount customer-nme Downtown Redwood -70 L Jones Smith lon left orrower (left outer join) rnch-nme lon-numer mount customer-nme lon-numer Downtown Redwood Perryridge -70 L-30 L Jones Smith null -70 L-30 null

32 Exmple Outer join cont... lon right orrower (nturl right outer join) rnch-nme Downtown Redwood null lon-numer L-70 L-30 L- mount null lon full orrower (nturl full outer join) customer-nme Jones Smith Hyes rnch-nme lon-numer mount customer-nme Downtown Redwood Perryridge null L-70 L-30 L-60 L null Jones Smith null Hyes