SQLSQL asas DataData ManipulationManipulation LanguageLanguage (DML)(DML)

Insert and update data Simple SQL queries Advanced SQL queries Views SQLSQL // DML:DML: OverviewOverview

Insert, update, delete data

Query data ƒ Interactively ƒ (Embedded in host language)

Data presentation to users ƒ Output improvements

FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ Views Hinze / Scholz

2 SQLSQL // DML:DML: InsertInsert datadata

Complete form: ƒ Predefined order of values

INSERT INTO Customer VALUES (001, 'Müller', 'Tina', NULL,NULL);

Incomplete form: ƒ Free order of values FU-Berlin, DBS I 2006, FU-Berlin, DBS INSERT INTO Customer (last_name, mem_no) VALUES ('Müller', 001); Hinze / Scholz

3 SQLSQL // DML:DML: InsertInsert datadata

Inserting dates

INSERT INTO movie VALUES (95, 'Psycho', 'suspense', TO_DATE('1969', 'yyyy'), 'Hitchcock', 2.00, NULL);

Conversion functions ƒ String to date

FU-Berlin, DBS I 2006, FU-Berlin, DBS TO_DATE([,]) ORACLE/Postgres

ƒ Date to string

Hinze / Scholz TO_CHAR([,]) ORACLE/Postgres

4 SQLSQL // DML:DML: InsertInsert datadata

Loading data from files ƒ System dependent  Oracle: ƒ INSERT INTO … ƒ Bulk load from file: SQL loader ƒ Bulk load from other database: export / import tool  MySQL: ƒ INSERT INTO … ƒ Bulk load: LOAD DATA … ƒ Bulk load from other database: FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT … INTO OUTFILE, LOAD DATA…  Postgres: ƒ INSERT INTO …

Hinze / Scholz ƒ Bulk load: Copy … ƒ Bulk load from other database: Copy … 5 SQLSQL // DML:DML: ImplementationsImplementations ofof bulkbulk loadload

Oracle SQL loader control file data file

SQL*Loader rejected field processing rows discarded rows record selection bad file FU-Berlin, DBS I 2006, FU-Berlin, DBS

(discard file) log file Oracle server Hinze / Scholz

6 SQLSQL // DML:DML: ImplementationsImplementations ofof bulkbulk loadload

loadtest.dat Example: CREATE TABLE loadtest( name varchar(20), 'four''four' ,, 44 num number(10,2)); 'five''five' ,, 55 'six''six' ,, 66 Oracle Syntax: sqlldr / loadtest.ctl loadload data data infileinfile 'loadtest.dat' 'loadtest.dat'

FU-Berlin, DBS I 2006, FU-Berlin, DBS badfilebadfile 'loadtest.bad' 'loadtest.bad' discardfilediscardfile 'loadtest.dis' 'loadtest.dis' APPENDAPPEND INTOINTO tabletable loadtest loadtest fieldsfields terminated terminated by by " " ,, "" Hinze / Scholz optionallyoptionally enclosed enclosed by by " " '' "" (name(name char, char, numnum integer integer external)external) 7 SQLSQL // DML:DML: ImplementationsImplementations ofof bulkbulk loadload

MySQL Example:

Mysql>Mysql> LOADLOAD DATADATA INFILEINFILE 'loadtest.dat''loadtest.dat' ->-> IGNOREIGNORE ->-> INTOINTO TABLETABLE loadtestloadtest ->-> FIELDSFIELDS ->-> TERMINATEDTERMINATED BYBY ",""," ->-> OPTIONALLYOPTIONALLY ENCLOSEDENCLOSED BYBY '''' ->-> (name,(name, numnum ); ); QueryQuery OK,OK, 33 rowsrows affected affected (0.01 (0.01 sec)sec) Records:Records: 33 Deleted:0Deleted:0 Skipped:Skipped: 00 Warnings:Warnings: 00 FU-Berlin, DBS I 2006, FU-Berlin, DBS Hinze / Scholz

8 SQLSQL // DML:DML: InsertInsert uniqueunique datadata

For synthetic keys, e.g. tapeId, …

Counter-variables in application not sufficient ƒ Session dependent ƒ Concurrent access problematic

Counter relation in database ƒ Expensive

FU-Berlin, DBS I 2006, FU-Berlin, DBS Proprietary solutions in existing DBMS MySQL: autoincrement keyword SQL-Server: identity keyword

Hinze / Scholz PostgreSQL: serial type and sequence Oracle: sequence-object 9 SQLSQL // DML:DML: InsertInsert uniqueunique datadata -- sequencesequence

Abstract sequence-object (Oracle) ƒ Creates unique integer values

Syntax: CREATE SEQUENCE [START WITH ] [INCREMENT BY ] [MAXVALUE | NOMINVALUE] [MINVALUE | NOMAXVALUE] [CYCLE | NOCYCLE] [CACHE | NOCACHE] FU-Berlin, DBS I 2006, FU-Berlin, DBS [ORDER | NOORDER];

Hinze / Scholz Example: create sequence tape_sequence;

10 SQLSQL // DML:DML: InsertInsert uniqueunique datadata -- sequencesequence

Value Access ƒ .NEXTVAL = value of last call + increment ƒ .CURRVAL = value of last call

ƒ SELECT .CURRVAL FROM DUAL; ƒ DUAL is Oracle pseudo-table

Example:

FU-Berlin, DBS I 2006, FU-Berlin, DBS INSERT INTO tape VALUES(tape_sequence.nextval, 'DVD', 95); Hinze / Scholz

11 SQLSQL // DML:DML: DeleteDelete datadata

Syntax: DELETE from [WHERE ];

ƒ Delete all rows : DELETE from ;

Example:

FU-Berlin, DBS I 2006, FU-Berlin, DBS DELETE from tape WHERE format= 'Beta'; Hinze / Scholz

12 SQLSQL // DML:DML: UpdateUpdate datadata

Syntax: UPDATE SET = {, = } WHERE

Examples: UPDATE Customer SET telephone = 456789 WHERE mem_no = 200;

UPDATE Rental

FU-Berlin, DBS I 2006, FU-Berlin, DBS SET until_date = SYSDATE WHERE tape_ID = 3 AND mem_no = 200 AND TO_CHAR(from_date,'yyyy-mm-dd')='2002-05-01'; Hinze / Scholz

13 SQLSQL // DML:DML: ExampleExample databasedatabase

insert into customer values (001, 'Müller', 'Tina', NULL,NULL); insert into customer values (007, 'Katz', 'Anna', NULL,NULL); insert into customer values (002, 'Maus', 'Carla', NULL,NULL); ....

insert into movie values (95, 'Psycho', 'suspense', to_date('1969', 'yyyy'), 'Hitchcock', 2.00, NULL); insert into movie values (112, 'ET', 'comedy', to_date('1982', 'yyyy'), 'Spielberg', 1.50, NULL); ....

insert into format values('DVD', '2.00'); insert into format values('Beta', '0.00'); insert into format values('VHS', '0.00'); FU-Berlin, DBS I 2006, FU-Berlin, DBS

create sequence tape_sequence; insert into tape values (tape_sequence.nextval, 'DVD', 95);

Hinze / Scholz insert into tape values (tape_sequence.nextval, 'DVD', 112); insert into tape values (tape_sequence.nextval, 'VHS', 222); 14 SQLSQL // DML:DML: ExampleExample databasedatabase

insert into rental values (3, 1, to_date('2002-05-01','yyyy-mm-dd'), NULL); insert into rental values (4, 1, to_date('2002-05-01','yyyy-mm-dd'), NULL); insert into rental values (5, 3, to_date('2002-05-01','yyyy-mm-dd'), to_date('2002-05-02','yyyy-mm-dd'));

insert into actor values ('Hitchcock', 'Hitchcock', to_date(1899-08-13','yyyy-mm-dd')); insert into actor values ('Harrison Ford', 'Harrison Ford', to_date('1942-07-13','yyyy-mm-dd')); FU-Berlin, DBS I 2006, FU-Berlin, DBS

insert into play values(290,'Harrison Ford'); insert into play values(98,'Hitchcock'); Hinze / Scholz

15 SQLSQL // DML:DML: QueryingQuerying LanguageLanguage

 SQL is relational complete

 Additional query concepts

ƒ Advanced search expressions on strings e.g., find all movies starting with “star wars”

ƒ Arithmetic in expressions, e.g., number of tapes for each movie FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ Grouping and predicates over sets e.g., total receipts of each movie within the last year Hinze / Scholz

16 SQLSQL // DML:DML: BasicsBasics

Basic query pattern:

SELECT [DISTINCT] A1, A2,...,An FROM R1, R2,...Rm WHERE predicate P;

ƒ A1 , A2 , ..., An attribute names,

ƒ R1 , R2 , ..., Rm relation names, ƒ P Boolean predicate on attributes and constants

Equivalent to relational algebra expression: FU-Berlin, DBS I 2006, FU-Berlin, DBS Π A1, A2, ..., An ( σP ( R1 X R2 X ... X Rm ))

ƒ Projection (RA) → SELECT (SQL)

Hinze / Scholz ƒ Cartesian Product (RA) → FROM (SQL) ƒ Selection (RA) → WHERE (SQL) 17 SQLSQL // DML:DML: BasicsBasics

Query result is relation

Query evaluation order: 1.FROM-clause 2.WHERE-clause 3.SELECT-clause SQL>SQL> SELECTSELECT last_namelast_name 22 FROMFROM Customer;Customer; No duplicate removal LAST_NAME (performance!) LAST_NAME ------FU-Berlin, DBS I 2006, FU-Berlin, DBS MüllerMüller KatzKatz MausMaus HinzHinz Hinze / Scholz KunzKunz MüllerMüller 18 SQLSQL // DML:DML: BasicsBasics

 Eliminating duplicates: ƒ Targetlist contains KEY attribute ƒ Targetlist constrains UNIQUE attribute ƒ Targetliste defined with DISTINCT

SELECT mem_no, last_name SELECT DISTINCT last_name FROM Customer FROM Customer MEM_NOMEM_NO LAST_NAMELAST_NAME LAST_NAMELAST_NAME ------11 MüllerMüller HinzHinz 77 KatzKatz KatzKatz FU-Berlin, DBS I 2006, FU-Berlin, DBS 22 MausMaus KunzKunz 1111 HinzHinz MausMaus 2323 KunzKunz MüllerMüller 111111 MüllerMüller Hinze / Scholz

19 SQLSQL // DML:DML: BasicsBasics

 WHERE-clause structure:

ƒ Simple Boolean predicates similar to RA and Calculus

ƒ Additional simple predicates: BETWEEN AND IS [NOT] NULL LIKE SIMILAR TO

FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ Advanced predicated with sub-queries Set-operators (IN, NOT IN, SOME, ALL, EXISTS) Hinze / Scholz

20 SQLSQL // DML:DML: SimpleSimple queriesqueries

Example: All customers named Anna SQL>SQL> selectselect mem_no, mem_no, last_name,last_name, first_namefirst_name 22 fromfrom customer customer 33 wherewhere first_name='Anna'; first_name='Anna';

MEM_NOMEM_NO LAST_NAMELAST_NAME FIRST_NAMEFIRST_NAME ------77 KatzKatz AnnaAnna 2323 KunzKunz AnnaAnna

Example: All movies by Lucas from 1999 or later SQL>SQL> selectselect id,id, titletitle 2 from movie

FU-Berlin, DBS I 2006, FU-Berlin, DBS 2 from movie 33 wherewhere director='Lucas'director='Lucas' 44 andand to_char(year,'yyyy')>='1999';to_char(year,'yyyy')>='1999';

IDID TITLETITLE Hinze / Scholz ------345345 StarStar WarsWars II 21 SQLSQL // DML:DML: SimpleSimple queriesqueries

More examples:

All formats with extra charge between 1 and 2 Euro SELECT * FROM Format WHERE charge BETWEEN 1.00 and 2.00;

All tapes currently on loan FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT tape_id FROM Rental WHERE until_date IS NULL; Hinze / Scholz

22 SQLSQL // DML:DML: SimpleSimple queriesqueries -- expressionsexpressions Core LIKE - expression SQL:1999 ƒ Simple form of regular expression ƒ % : any sequence of characters ƒ _ : exactly one character

Example: All ‘star wars’ movies

SQL>SQL> selectselect id,id, title,title, directordirector 22 fromfrom moviemovie 33 wherewhere titletitle likelike 'Star'Star WarsWars %';%'; FU-Berlin, DBS I 2006, FU-Berlin, DBS IDID TITLETITLE DIRECTORDIRECTOR ------345345 StarStar WarsWars II LucasLucas

Hinze / Scholz 290290 StarStar WarsWars IVIV LucasLucas

23 SQLSQL // DML:DML: SimpleSimple queriesqueries -- expressionsexpressions enhanced SIMILAR - expression SQL:1999 ƒ Advanced form of regular expression

Example:

All ‘star wars’ movies SELECT id, title, director FROM movie WHERE title SIMILAR TO

FU-Berlin, DBS I 2006, FU-Berlin, DBS 'Star Wars (I | IV | V | VI | 1 | [4-6])'; Hinze / Scholz

24 SQLSQL // DML:DML: SimpleSimple queriesqueries

Member in set: IN

All movies from Spielberg or Lukas Core SELECT title, director SQL:1999 FROM Movie WHERE director IN ('Spielberg','Lucas');

All movies from Lucas in 1999 enhanced SELECT title, director SQL:1999 FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Movie WHERE (director, year) IN (('Lucas',to_date(1999,'yyyy'))); Hinze / Scholz

25 SQLSQL // DML:DML: SimpleSimple queriesqueries -- expressionsexpressions

Functions ƒ Expressions may contain functions ƒ Arithmetical and string built-in functions ƒ User defined functions on user defined types

String function examples: ƒ SOUNDEX (), UPPER () ƒ SUBSTRING( FROM FOR )

SQL>SQL> SELECTSELECT title,title, directordirector 22 FROMFROM MovieMovie FU-Berlin, DBS I 2006, FU-Berlin, DBS 33 WHEREWHERE SOUNDEX(directorSOUNDEX(director)) == SOUNDEX('Spilbak');SOUNDEX('Spilbak');

TITLETITLE DIRECTORDIRECTOR ------Hinze / Scholz ETET SpielbergSpielberg PsychoPsycho SpielbergSpielberg JawsJaws SpielbergSpielberg 26 SQLSQL // DML:DML: SimpleSimple queriesqueries -- expressionsexpressions

Arithmetic function examples ƒ SQRT() ƒ Basic arithmetic expressions

All tapes, their price and tax SQL>SQL> SELECTSELECT id,id, pricepday,pricepday, 22 0.16*pricepday0.16*pricepday as as taxtax 33 FROMFROM Movie;Movie;

IDID PRICEPDAYPRICEPDAY TAXTAX ------FU-Berlin, DBS I 2006, FU-Berlin, DBS 9595 22 .32.32 112112 1.51.5 .24.24 345345 22 .32.32 222 2.2 .352

Hinze / Scholz 222 2.2 .352 290290 22 .32.32 100 1.5 .24 100 1.5 .24 27 SQLSQL // DML:DML: SimpleSimple queriesqueries -- expressionsexpressions

Date function examples ƒ differ heavily between systems

ƒ Oracle: SYSDATE, MONTHS_BETWEEN, ADD_MONTHS

SQL>SQL> SELECTSELECT title,title, to_char(to_char(year,'yyyy')year,'yyyy') asas yearyear 22 FROMFROM moviemovie 33 WHEREWHERE months_BETWmonths_BETWEEN(SYSDATE,year)>EEN(SYSDATE,year)> 120120 ;;

TITLETITLE YEARYEAR ------FU-Berlin, DBS I 2006, FU-Berlin, DBS PsychoPsycho 19691969 ETET 19821982 JawsJaws 19751975 Hinze / Scholz

28 SQLSQL // DML:DML: SimpleSimple queriesqueries Core Combination of relations SQL:1999 ƒ Schema compatible relations ƒ UNION, INTERSECT, EXCEPT

Syntax: UNION | INTERSECT | EXCEPT [DISTINCT | ALL] [CORRESPONDING [BY ]]

ƒ Default DISTINCT FU-Berlin, DBS I 2006, FU-Berlin, DBS

ƒ Default: all attributes used ƒ CORRESPONDING BY: defines used common attributes Hinze / Scholz ƒ CORRESPONDING: uses all common attributes 29 SQLSQL // DML:DML: SimpleSimple queriesqueries

Example:

All movies from Spielberg or Lukas (SELECT title, director FROM Movie WHERE director like 'Spielberg') UNION (SELECT title, director FROM Movie WHERE director like 'Lucas'); FU-Berlin, DBS I 2006, FU-Berlin, DBS Hinze / Scholz

30 SQLSQL // DML:DML: SimpleSimple queriesqueries

More examples: All movies not by Lucas (SELECT * FROM Movie) EXCEPT (SELECT * from Movie WHERE director='Lucas');

All directors and actors in our database

FU-Berlin, DBS I 2006, FU-Berlin, DBS (SELECT director as celebrity FROM Movie) UNION DISTINCT (SELECT stage_name as celebrity Hinze / Scholz FROM Actor);

31 SQLSQL // DML:DML: ImplementationsImplementations combinationscombinations

Oracle: ƒ UNION ƒ MINUS implements EXCEPT ƒ INTERSECT ƒ CORRESPONDING [BY] not implemented

PostgreSQL: ƒ UNION ƒ EXCEPT ƒ INTERSECT FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ CORRESPONDING [BY] not implemented

 Hinze / Scholz MySQL: ƒ UNION, EXCEPT, INTERSECT not implemented 32 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins Core Simple joins SQL:1999 ƒ Search predicates and join conditions mixed

Example: All Tapes and their corresponding movie

SQL>SQL> SELECTSELECT t.id,t.id, t.fot.format,rmat, m.id,m.id, m.titlem.title 22 FROMFROM TapeTape t,t, MovieMovie mm 33 WHEREWHERE m.idm.id == t.movie_id;t.movie_id;

IDID FORMATFORMAT IDID TITLETITLE

------FU-Berlin, DBS I 2006, FU-Berlin, DBS 11 DVDDVD 9595 PsychoPsycho 22 DVDDVD 112112 ETET 33 VHSVHS 222222 PsychoPsycho 44 DVDDVD 345345 StarStar WarsWars II Hinze / Scholz 55 VHSVHS 345345 StarStar WarsWars II 99 VHSVHS 345345 StarStar WarsWars II 33 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins enhanced Cross join (cross product) SQL:1999

CROSS JOIN

Natural inner join

NATURAL [INNER] JOIN

Example: FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT * FROM Rental NATURAL INNER JOIN Customer; Hinze / Scholz

34 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins enhanced Inner join with attribute list SQL:1999

[INNER] JOIN USING

Subset of attributes in common

Example: SELECT *

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Rental r JOIN Customer c USING (mem_no); Hinze / Scholz

35 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins enhanced Inner join with condition SQL:1999 [INNER] JOIN ON

Examples: SELECT * FROM Tape t JOIN Movie m ON t.movie_id = m.id;

FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT * FROM Rental r JOIN Customer c ON r.mem_no = c.mem_no; Hinze / Scholz

36 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins

All Customers who have rented at least one science fiction film

SELECT c.mem_no, c.last_name, c.first_name FROM ((Customer c JOIN Rental r ON c.mem_no = r.mem_no) JOIN Tape t ON t.id = r.tape_id ) JOIN Movie m ON t.movie_id = m.id WHERE m.category='Scifi';

SELECT c.mem_no, c.last_name, c.first_name

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Customer c, Rental r, Tape t, Movie m WHERE c.mem_no=r.mem_no AND t.id = r.tape_id AND t.movie_id = m.id Hinze / Scholz AND m.category='Scifi';

37 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins enhanced Natural outer join SQL:1999 LEFT|RIGHT|FULL NATURAL [OUTER] JOIN

Outer join with condition LEFT|RIGHT|FULL [OUTER] JOIN ON

FU-Berlin, DBS I 2006, FU-Berlin, DBS Example: SELECT * FROM Rental r RIGHT OUTER JOIN Customer c

Hinze / Scholz ON r.mem_no = c.mem_no;

38 SQLSQL // DML:DML: SimpleSimple queriesqueries withwith joinsjoins

Example (extended)

SQL>SQL> SELECTSELECT r.tape_id,r.tape_id, r.frr.from_date,om_date, c.mem_no,c.first_namec.mem_no,c.first_name 22 FROMFROM RentalRental r r RIGHTRIGHT OUTEROUTER JOINJOIN CustomerCustomer c c 33 ONON r.mem_nor.mem_no = = c.mem_no;c.mem_no;

TAPE_IDTAPE_ID FROM_DATEFROM_DATE MEM_NOMEM_NO FIRST_NAMEFIRST_NAME ------33 01-MAY-0201-MAY-02 11 TinaTina 44 01-MAY-0201-MAY-02 11 TinaTina 55 01-MAY-0201-MAY-02 22 CarlaCarla 2323 AnnaAnna 111111 BertBert FU-Berlin, DBS I 2006, FU-Berlin, DBS 1111 FritzFritz 77 AnnaAnna Hinze / Scholz

39 SQLSQL // DML:DML: ImplementationsImplementations ofof joinsjoins

Oracle/Postgres: ƒ Simple join ƒ Cross join ƒ (natural) inner join with attribute list, with condition ƒ (natural) Right, left, full outer join with condition

ƒ recommends ANSI-syntax for compatibility

MySQL: ƒ Simple join FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ Cross join ƒ Straight join (left table always read before right one) ƒ Inner join with condition Hinze / Scholz ƒ (natural) left, right outer join with condition

40 SQLSQL // DML:DML: ImprovingImproving thethe outputoutput

Not feature of relational algebra Example: ƒ Rename column title for this query ƒ Order tuples

SQL>SQL> SELECTSELECT m.titlem.title asas Movies,Movies, t.id,t.id, t.formatt.format 22 FROMFROM MovieMovie m,m, TapeTape tt 33 WHEREWHERE m.idm.id == t.movie_idt.movie_id 44 ORDERORDER BYBY title;title;

MOVIESMOVIES IDID FORMATFORMAT ------

FU-Berlin, DBS I 2006, FU-Berlin, DBS ------ETET 22 DVDDVD PsychoPsycho 11 DVDDVD PsychoPsycho 33 VHSVHS StarStar WarsWars II 44 DVDDVD Hinze / Scholz StarStar WarsWars II 55 VHSVHS StarStar WarsWars II 99 VHSVHS 41 SQLSQL // DML:DML: ImprovingImproving thethe outputoutput

Syntax: ORDER BY ASC|DESC

Ordering expression ƒ No advanced expressions (no sub-query, no grouping) ƒ At least one attribute reference ƒ References in order expression ⊆ result attributes

Multiple sort attributes: ƒ Primary ordering by first attribute

FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ Secondary ordering by second attribute, … SELECT m.title as Movies, t.id, t.format FROM Movie m, Tape t

Hinze / Scholz WHERE m.id = t.movie_id ORDER BY title, format; 42 SQLSQL // DML:DML: ImprovingImproving thethe outputoutput

Advanced features system dependent Oracle SQL+ Example: ƒ Format column title for all queries ƒ Don’t repeat identical titles SQL>SQL> BREAKBREAK ONON titletitle SQL>SQL> COLUMNCOLUMN titletitle HEADHEADINGING "Movies""Movies" FORMATFORMAT A15A15

SQL>SQL> SELECTSELECT m.title,m.title, t.id,t.id, t.formatt.format 22 FROMFROM MovieMovie m,m, TapeTape tt 33 WHEREWHERE m.idm.id == t.movie_id;t.movie_id;

Movies ID FORMAT

FU-Berlin, DBS I 2006, FU-Berlin, DBS Movies ID FORMAT ------PsychoPsycho 11 DVDDVD ETET 22 DVDDVD PsychoPsycho 3 3 VHSVHS Hinze / Scholz StarStar WarsWars II 44 DVDDVD 55 VHSVHS 99 VHSVHS 43 SQLSQL // DML:DML: SubSub--queriesqueries Core Sub-queries with single results SQL:1999 ƒ Operators {=, ≤, ≥, ≠, <, >} ƒ Expressible without sub-query

Example: Movies shorter than 'Star Wars I‘ (id 345)

SELECT m.id FROM Movie m

FU-Berlin, DBS I 2006, FU-Berlin, DBS WHERE m.length < (SELECT m1.length FROM Movie m1 WHERE m1.id = 345); Hinze / Scholz

44 SQLSQL // DML:DML: SubSub--queriesqueries Core Set Operator IN SQL:1999

Independent sub-query example:

All Tapes for movie ‘Star Wars ’

SELECT t.id, t.format FROM Tape t WHERE t.movie_id IN (SELECT m.id

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Movie m WHERE m.title like 'Star Wars %'); Hinze / Scholz

45 SQLSQL // DML:DML: SubSub--queriesqueries Core Set Operator IN SQL:1999

Correlated sub-query example:

Directors playing in their own movies

SELECT m.director FROM Movie m WHERE m.director IN (SELECT p.actor_name

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Play p WHERE p.movie_id = m.id); Hinze / Scholz

46 SQLSQL // DML:DML: SubSub--queriesqueries Core Alternative syntax: EXISTS SQL:1999

Example: SELECT t.id, t.format FROM Tape t WHERE EXISTS (SELECT * FROM Movie m WHERE t.movie_id = m.id AND m.title like 'Star Wars %');

FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT m.director FROM Movie m WHERE EXISTS (SELECT * FROM Play p Hinze / Scholz WHERE p.movie_id = m.id AND m.director like p.actor_name); 47 SQLSQL // DML:DML: QueryQuery rewritingrewriting

Rewriting possible for IN, EXISTS

Examples:

SELECT t.id, t.format FROM Tape t, Movie m WHERE m.id = t.movie_id AND m.title like 'Star Wars %';

SELECT m.director FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Movie m, Play p WHERE p.movie_id = m.id AND m.director like p.actor_name; Hinze / Scholz

48 SQLSQL // DML:DML: SubSub--queriesqueries Core Negation NOT EXISTS, NOT IN SQL:1999

All tapes that never have been on loan SELECT t.id FROM Tape t WHERE NOT EXISTS (SELECT * FROM Rental r WHERE r.tape_id = t.id);

All movies no copy of which are currently on loan SELECT distinct m.id

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Movie m Where NOT EXISTS (SELECT * FROM Rental r, Tape t WHERE r.tape_id = t.id Hinze / Scholz AND m.id = t.movie_id AND r.until_date IS NULL); 49 SQLSQL // DML:DML: QuantifiedQuantified subsub--queriesqueries enhanced Quantified comparison operators SQL:1999 ƒ No re-writing without sub-query ƒ Quantification: ALL, SOME (synonym ANY) ƒ Operators ∈ {=, ≤, ≥, ≠, <, >}

Quantification All ƒ Sub-query true if true for all tuples

Most expensive movies FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT m.id, m.pricepday FROM Movie m WHERE m.pricepday >= ALL (SELECT m1.pricepday Hinze / Scholz FROM MOVIE m1);

50 SQLSQL // DML:DML: QuantifiedQuantified subsub--queriesqueries enhanced Quantification: SOME SQL:1999 ƒ Sub-query true if true for at least one tuple

SELECT title, pricePDay FROM Movie m WHERE pricePday < SOME (SELECT m1.pricepday FROM Movie m1);

ƒ = SOME equivalent IN

FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT m.director FROM Movie m WHERE m.director = SOME (SELECT p.actor_name

Hinze / Scholz FROM Play p WHERE p.movie_id = m.id); 51 SQLSQL // DML:DML: ImplementationsImplementations ofof subsub--queriesqueries

Oracle: ƒ Sub-queries with single results ƒ Sub-queries with [NOT] IN, [NOT] EXISTS ƒ Quantified comparison ALL, SOME, ANY

PostgreSQL ƒ Similar to Oracle FU-Berlin, DBS I 2006, FU-Berlin, DBS MySQL: ƒ No sub-queries supported Hinze / Scholz

52 SQLSQL // DML:DML: UniversalUniversal quantifiersquantifiers

∀ – Quantification ∃ - Quantification (exactly one) ƒ Describe counterexample ƒ Combine with NOT EXISTS

Movies with only one tape SELECT m.id FROM Movie m WHERE NOT EXISTS (SELECT * FROM Tape t1, Tape t2 FU-Berlin, DBS I 2006, FU-Berlin, DBS WHERE t1.movie_id = t2.movie_id AND t1.id <> t2.id AND t2.movie_id = m.id ); Hinze / Scholz

53 SQLSQL // DML:DML: UniversalUniversal quantifiersquantifiers

All Customers whose rented movies all have category “suspense“

SELECT c.mem_no FROM Customer c WHERE NOT EXISTS (SELECT m.id FROM Movie m, Rental r, Tape t WHERE m.id = t.movie_id AND r.tape_id = t.id AND c.mem_no = r.mem_no AND m.category <> 'suspense'); FU-Berlin, DBS I 2006, FU-Berlin, DBS Hinze / Scholz

54 SQLSQL // DML:DML: UniversalUniversal quantifiersquantifiers

Customers that had rented all movies

SELECT c.mem_no FROM Customer c WHERE NOT EXISTS (SELECT m.id FROM Movie m WHERE NOT EXISTS (SELECT * FROM Rental r, Tape t WHERE m.id = t.movie_id AND r.tape_id = t.id FU-Berlin, DBS I 2006, FU-Berlin, DBS AND c.mem_no = r.mem_no)); Hinze / Scholz

55 SQLSQL // DML:DML: UniversalUniversal quantifiersquantifiers

Customers that rented only one movie

SELECT c.mem_no FROM Customer c, Rental r, Tape t, Movie m WHERE c.mem_no = r.mem_no AND r.tape_id = t.id AND t.movie_id = m.id AND NOT EXISTS (SELECT m1.id FROM Rental r1, Tape t1, Movie m1 WHERE r1.tape_id = t1.id AND t1.movie_id = m1.id FU-Berlin, DBS I 2006, FU-Berlin, DBS AND c.mem_no = r1.mem_no AND m1.id <> m.id); Hinze / Scholz

56 SQLSQL // DML:DML: AggregateAggregate functionsfunctions

Mathematical aggregate functions on data sets Example: SUM, AVG, MIN, MAX, COUNT Not in relational algebra

SQL>SQL> SELECTSELECT MIN(pricePDay)MIN(pricePDay) asas MIN,MIN, 22 MAX(pricePDay)MAX(pricePDay) asas MAX,MAX, AVG(pricePDay)AVG(pricePDay) 33 FROMFROM Movie;Movie;

MINMIN MAXMAX AVG(PRICEPDAY)AVG(PRICEPDAY) ------1.51.5 2.22.2 1.866666671.86666667 FU-Berlin, DBS I 2006, FU-Berlin, DBS

Target list: only aggregate functions or none

Hinze / Scholz ƒ Exception: GROUP BY

57 SQLSQL // DML:DML: AggregateAggregate functionsfunctions

Comparison using aggregates: sub-queries

Movies with price above average

SQL>SQL> SELECTSELECT m.id,m.id, m.Title,m.Title, m.pricepdaym.pricepday 22 FROMFROM MovieMovie mm 33 WHEREWHERE pricePDaypricePDay > > 44 (SELECT(SELECT AVG(pricePDay)AVG(pricePDay) 55 FROMFROM Movie);Movie);

IDID TITLETITLE PRICEPDAYPRICEPDAY ------FU-Berlin, DBS I 2006, FU-Berlin, DBS 9595 PsychoPsycho 22 345345 StarStar WarsWars II 22 222222 PsychoPsycho 2.22.2 290290 StarStar WarsWars IVIV 22 Hinze / Scholz

58 SQLSQL // DML:DML: AggregateAggregate functionsfunctions

Examples:

Movies with minimal price SELECT m.Title, m.pricepday FROM Movie m WHERE pricePDay = (SELECT MIN(pricePDay) FROM Movie);

Movie with more than 2 tapes

FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT m.id, m.title FROM Movie m WHERE 2 < (SELECT count(t.id) FROM tape t Hinze / Scholz WHERE t.movie_id = m.id)

59 SQLSQL // DML:DML: AggregateAggregate functionsfunctions

More examples:

Movies having tapes in one format only SELECT m.id, m.title FROM Movie m, Tape t1 WHERE m.id = t1.movie_id AND 0 = (SELECT COUNT(*) FROM Tape t2 WHERE t1.id <> t2.id AND t1.format <> t2.format FU-Berlin, DBS I 2006, FU-Berlin, DBS AND t2.movie_id = m.id); Hinze / Scholz

60 SQLSQL // DML:DML: AggregateAggregate functionsfunctions

Additional qualification with DISTINCT | ALL

Example:

Movies that are available in all formats SELECT DISTINCT t1.movie_id FROM Tape t1 WHERE (SELECT COUNT(DISTINCT format) FROM Tape t2 WHERE t2.movie_id = t1.movie_id) FU-Berlin, DBS I 2006, FU-Berlin, DBS = (SELECT COUNT(*) FROM Format); Hinze / Scholz

61 SQLSQL // DML:DML: GroupingGrouping

Syntax: SELECT FROM [WHERE ] GROUP BY

Groups all rows with same values in Target list: grouping attributes and aggregates

Example:

FU-Berlin, DBS I 2006, FU-Berlin, DBS Number of tapes in each format SELECT t.format, count(t.id) FROM Tape t

Hinze / Scholz GROUP BY t.format;

62 SQLSQL // DML:DML: GroupingGrouping

Aggregates evaluated over groups

Number of tapes for each movie

SQL>SQL> SELECTSELECT t.movie_id,t.movie_id, count(*)count(*) 22 FROMFROM TapeTape tt 33 GROUPGROUP BYBY t.movie_id;t.movie_id;

MOVIE_IDMOVIE_ID COUNT(*)COUNT(*) ------9595 11 100100 11 FU-Berlin, DBS I 2006, FU-Berlin, DBS 112112 11 222222 11 290290 11 345 4

Hinze / Scholz 345 4

63 SQLSQL // DML:DML: GroupingGrouping

Movie id title cat. year director price leng. 095 Psycho ...... Hitchcock 2.00 ... 112 ET ...... Spielberg 1.50 ... 345 Star Wars I ...... Lucas 2.00 ... 222 Psycho ...... Van Sant 2.20 ... 290 Star Wars IV ...... Lucas 2.00 ... 100 Jaws ...... Spielberg 1.50 ......

FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT sum(price) 11.2 FROM movie;

Hinze / Scholz Implicit group: all tuples in table

64 SQLSQL // DML:DML: GroupingGrouping

Movie id title cat. year director price leng. 095 Psycho ...... Hitchcock 2.00 ... 112 ET ...... Spielberg 1.50 ... 345 Star Wars I ...... Lucas 2.00 ... 222 Psycho ...... Van Sant 2.20 ... 290 Star Wars IV ...... Lucas 2.00 ... 100 Jaws ...... Spielberg 1.50 ......

Hitchcock 2.0 FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT director, sum(price) Spielberg 3.0 FROM movie Lucas 4.0 Group by director; Van Sant 2.2 Hinze / Scholz

65 SQLSQL // DML:DML: GroupingGrouping

Total receipts of each tape within the last year

SQL>SQL> SELECTSELECT t.id,t.id, count(*)count(*) 22 FROMFROM TapeTape t,t, RentalRental rr 33 WHEREWHERE t.idt.id = = r.tape_idr.tape_id 44 ANDAND to_char(r.from_date,'yyyy')to_char(r.from_date,'yyyy') >=>= 20052005 55 GROUPGROUP BYBY t.id;t.id;

IDID COUNT(*)COUNT(*) ------11 11 22 11 FU-Berlin, DBS I 2006, FU-Berlin, DBS 33 22 44 22 55 11 1111 11 Hinze / Scholz 1212 11

66 SQLSQL // DML:DML: GroupingGrouping

Total receipts of each movie within the last year

SQL>SQL> SELECTSELECT t.movie_id,t.movie_id, count(*)count(*) 22 FROMFROM TapeTape t,t, RentalRental rr 33 WHEREWHERE t.idt.id = = r.tape_idr.tape_id 44 ANDAND to_char(r.from_date,'yyyy')to_char(r.from_date,'yyyy') >=>= 20052005 55 GROUPGROUP BYBY t.movie_id;t.movie_id;

MOVIE_IDMOVIE_ID COUNT(*)COUNT(*) ------9595 11 100100 11 FU-Berlin, DBS I 2006, FU-Berlin, DBS 112112 11 222222 22 290290 11 345345 33 Hinze / Scholz

67 SQLSQL // DML:DML: GroupingGrouping ++ HavingHaving

 Qualifying predicate for groups

SQL>SQL> SELECTSELECT f.name,f.name, sum(charge)sum(charge) 22 FROMFROM RentalRental r, r, TapeTape t,t, formatformat f f 33 WHEREWHERE t.idt.id = = r.tape_idr.tape_id 44 ANDAND t.format=f.namet.format=f.name 55 GROUPGROUP BYBY f.name;f.name; SQL>SQL> SELECTSELECT f.name,f.name, sum(charge)sum(charge) NAMENAME SUM(CHARGE)SUM(CHARGE) 22 FROMFROM RentalRental r, r, TapeTape t,t, formatformat f f ------33 WHEREWHERE t.idt.id = = r.tape_idr.tape_id BetaBeta 00 44 ANDAND t.format=f.namet.format=f.name DVDDVD 88 55 GROUPGROUP BYBY f.namef.name FU-Berlin, DBS I 2006, FU-Berlin, DBS VHSVHS 00 66 havinghaving count(f.name)>2; count(f.name)>2;

NAMENAME SUM(CHARGE)SUM(CHARGE) ------Hinze / Scholz ------DVDDVD 88 VHSVHS 00 68 SQLSQL // DML:DML: GroupingGrouping ++ HavingHaving

Movie id title cat. year director price leng. 095 Psycho ...... Hitchcock 2.00 ... 112 ET ...... Spielberg 1.50 ... 345 Star Wars I ...... Lucas 2.00 ... 222 Psycho ...... Van Sant 2.20 ... 290 Star Wars IV ...... Lucas 2.00 ... 100 Jaws ...... Spielberg 1.50 ......

Hitchcock 2.0 FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT director, sum(price) Spielberg 3.0 FROM movie Lucas 4.0 Group by director Van Sant 2.2 HAVING sum(price)>2.00; Hinze / Scholz

69 SQLSQL // DML:DML: GroupingGrouping ++ HavingHaving

Movie id title cat. year director price leng. 095 Psycho ...... Hitchcock 2.00 ... 112 ET ...... Spielberg 1.50 ... 345 Star Wars I ...... Lucas 2.00 ... 222 Psycho ...... Van Sant 2.20 ... 290 Star Wars IV ...... Lucas 2.00 ... 100 Jaws ...... Spielberg 1.50 ...... max Hitchcock 2.0 2.0 FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT director, sum(price) Spielberg 3.0 1.5 FROM movie Lucas 4.0 2.0 Group by director Van Sant 2.2 2.2 HAVING max(price)>2.00; Hinze / Scholz

70 SQLSQL // DML:DML: GroupingGrouping ++ HavingHaving

Movie id title cat. year director price leng. 095 Psycho ...... Hitchcock 2.00 ... 112 ET ...... Spielberg 1.50 ... 345 Star Wars I ...... Lucas 2.00 ... 222 Psycho ...... Van Sant 2.20 ... 290 Star Wars IV ...... Lucas 2.00 ... 100 Jaws ...... Spielberg 1.50 ...... max Hitchcock, Psycho 2.0 2.0 FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT director,title, sum(price) Spielberg, ET 1.5 1.5 FROM movie Lucas, SW I 2.0 2.0 Group by director, title Van Sant, Psycho 2.2 2.2 HAVING max(price)>2.00; Hinze / Scholz Lucas, SW IV 2.0 2.0 Spielberg, Jaws 1.5 1.5 71 SQLSQL // DML:DML: GroupingGrouping ++ HavingHaving

 HAVING without GROUP BY ƒ Implicit single group contains all tuples

SQL>SQL> SELECTSELECT sum(charge)sum(charge) 22 FROMFROM RentalRental r, r, TapeTape t,t, formatformat f f 33 WHEREWHERE t.idt.id = = r.tape_idr.tape_id 44 ANDAND t.format=f.namet.format=f.name 55 havinghaving count(f.name)>2; count(f.name)>2;

SUM(CHARGE)SUM(CHARGE) ------

FU-Berlin, DBS I 2006, FU-Berlin, DBS 88 Hinze / Scholz

72 SQLSQL // DML:DML: GroupingGrouping ++ HavingHaving

Query evaluation order: 1.FROM-clause 2.WHERE-clause 3.GROUP BY–clause 4.HAVING-clause 5.SELECT-clause

Number of rentals for all customers named Anna or Tina, which rented some tapes more than once SELECT c.mem_no, count(*)

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Rental r, Customer c WHERE r.mem_no= c.mem_no AND c.first_name ='Anna' OR c.first_name='Tina' Hinze / Scholz GROUP BY c.mem_no HAVING count(DISTINCT r.tape_id)

Nested aggregation using groups

Most loaned movie

SELECT t.movie_id, count(t.movie_id) FROM Rental r, Tape t WHERE r.tape_id = t.id GROUP BY t.movie_id HAVING COUNT(t.movie_id) > = ALL (SELECT count(t1.movie_id) FROM Rental r1, Tape t1

FU-Berlin, DBS I 2006, FU-Berlin, DBS WHERE r1.tape_id = t1.id Group BY t1.movie_id); Hinze / Scholz

74 SQLSQL // DML:DML: NestedNested aggregationaggregation withwith groupsgroups

Movie with maximal number of tapes, show number of tapes

SELECT m.id, m.title, t1.t_no FROM (SELECT t.movie_id, count(*) as t_no FROM tape t GROUP BY t.movie_id) t1, movie m WHERE m.id=t1.movie_id AND t1.t_no = (SELECT max(count(*)) FROM tape t GROUP by t.movie_id); FU-Berlin, DBS I 2006, FU-Berlin, DBS Hinze / Scholz

75 SQLSQL // DML:DML: OutputOutput improvementimprovement Core Select values depending an condition SQL:1999 Complete CASE form: CASE WHEN THEN [ WHEN THEN [ WHEN THEN ]] [ ELSE ] END

Example:

FU-Berlin, DBS I 2006, FU-Berlin, DBS SELECT length, CASE WHEN length is NULL then 'not defined' WHEN length < 90 THEN 'short' ELSE 'long' Hinze / Scholz END FROM Movie; 76 SQLSQL // DML:DML: OutputOutput improvementimprovement Core Simple CASE form SQL:1999 CASE WHEN THEN [ WHEN THEN [ WHEN THEN ]] [ ELSE ] END

Example: select f.name, case f.name

FU-Berlin, DBS I 2006, FU-Berlin, DBS when 'DVD' then 'DISC' when 'Beta' then 'TAPE' when 'VHS' then 'TAPE' else NULL

Hinze / Scholz end from Format f; 77 SQLSQL // DML:DML: TransitiveTransitive closureclosure enhanced Recursive queries SQL:1999 ƒ Name recursion expression ƒ Use name in associated query expression

SYNTAX:

WITH RECURSIVE AS [, AS ,...] SELECT ... FROM [,...] FU-Berlin, DBS I 2006, FU-Berlin, DBS WHERE... Hinze / Scholz

78 SQLSQL // DML:DML: TransitiveTransitive closureclosure enhanced Example: All lectures required for lecture XYZ SQL:1999 create table lecture( lnr integer primary key, name varchar(20)); create table requires( pre integer references lecture(lnr), suc integer references lecture(lnr), constraint req_pk primary key(pre, suc));

WITH RECURSIVE preLecture(pre, suc)

FU-Berlin, DBS I 2006, FU-Berlin, DBS AS (SELECT pre,suc FROM requires) SELECT l.lnr as prerequisite FROM preLecture p1, preLecture p2, lecture l WHERE p2.suc = l.lnr

Hinze / Scholz AND l.name = ‘databases’ AND p1.suc = p2.pre; 79 SQLSQL // DML:DML: TransitiveTransitive closureclosure

Different implementation in oracle: Lecture:LNR NAME Requires: PRE SUC ------1 databases 2 3 2 algorithms I 3 1 3 algorithms II

SQL>SQL> SELECTSELECT r.prer.pre 22 FROMFROM requiresrequires r,r, lecturelecture ll 33 WHEREWHERE l.name=l.name= 'databases''databases' 44 STARTSTART WITHWITH r.sucr.suc = = l.lnrl.lnr FU-Berlin, DBS I 2006, FU-Berlin, DBS 55 CONNECTCONNECT BYBY PRIORPRIOR prepre == suc;suc;

PREPRE ------

Hinze / Scholz ------33 2 2 80 SQLSQL // DML:DML: StructuringStructuring enhanced Difficult structuring of complex queries SQL:1999 No naming of commands / relations for re-use

Temporary table CREATE TABLE {global temporary | local temporary }

[ON COMMIT {PRESERVE ROWS | DELETE ROWS}]

ƒ Stores temporal query result FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ LOCAL: Only visible to owner ƒ Dropped at end of session Hinze / Scholz

81 SQLSQL // DML:DML: TemporaryTemporary tabletable

Example: Test1: CREATE TABLE testsource(id integer); CREATE GLOBAL TEMPORARY TABLE test1(id integer) ON COMMIT PRESERVE ROWS; No rows

INSERT INTO testsource values(1); No rows

INSERT INTO test1 SELECT * FROM testsource; 1 FU-Berlin, DBS I 2006, FU-Berlin, DBS

INSERT INTO testsource values(2); 1

COMMIT; Hinze / Scholz 1

82 SQLSQL // DML:DML: TemporaryTemporary tabletable

Example: Test2: CREATE TABLE testsource(id integer); CREATE GLOBAL TEMPORARY TABLE test2(id integer) ON COMMIT DELETE ROWS; No rows

INSERT INTO testsource values(1); No rows

INSERT INTO test2 SELECT * FROM testsource; 1 FU-Berlin, DBS I 2006, FU-Berlin, DBS

INSERT INTO testsource values(2); 1

COMMIT; Hinze / Scholz No rows

83 SQLSQL // DML:DML: ViewView

SQL-object (virtual relation) Important concept Important for ƒ Tailoring database schema for different applications ƒ Access protection, Privacy ƒ Structuring complex queries Relational concept for external schema

Syntax: CREATE VIEW AS ;

FU-Berlin, DBS I 2006, FU-Berlin, DBS Example: CREATE VIEW rental_overview AS SELECT r.mem_no, c.last_name, r.tape_id

Hinze / Scholz FROM rental r, customer c WHERE r.mem_no = c.mem_no; 84 SQLSQL // DML:DML: ViewView updatesupdates Core  Updateable views: SQL:1999 1. No SELECT DISTINCT 2. No duplicate attribute in target list 3. Only one table reference 4. No GROUP BY 5. No aggregates 6. No set operators (INTERSECT, EXCEPT, UNION)

 Formal:

FU-Berlin, DBS I 2006, FU-Berlin, DBS u (V(B)) = V (cu (B) )

ƒ V(B) view on base tables B ƒ u(V(B)) update on view Hinze / Scholz ƒ cu : equivalent update(s) on base relations must exist

85 SQLSQL // DML:DML: ViewView updatesupdates Core  Examples: SQL:1999 ƒ Not updateable ( distinct, group by ): CREATE VIEW movieformats (movie, numFormats) AS SELECT movie_id, count(distinct format) FROM Tape t GROUP BY movie_id;

ƒ Updateable: CREATE VIEW movies (movie, name) AS SELECT id, title

FU-Berlin, DBS I 2006, FU-Berlin, DBS FROM Movie WHERE id > 100;

u: INSERT INTO movies VALUES (47,‘The Fugitive‘);

Hinze / Scholz INSERT INTO movie (id, title) cu: VALUES (47,‘The Fugitive‘); 86 SQLSQL // DML:DML: ViewView updatesupdates

Additional conditions:

ƒ If u does not have an effect, then cu should not

ƒ No side effects: c should only effect tuples in B which are represented in V

ƒ Inverse update: For a view update u there should be an inverse update w such that w (u ( V( B )) ) = V (B)

FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ No constraint on base tables must be violated by u Hinze / Scholz

87 SQLSQL // DML:DML: ViewView updatesupdates

Views with check option ƒ CHECK OPTION prevent side effects on base tables

Syntax: CREATE VIEW AS WITH CHECK OPTION;

Theoretically more views updateable ƒ e.g. UNIQUE columns in joins FU-Berlin, DBS I 2006, FU-Berlin, DBS

Enhanced SQL: ƒ 1999 additional complex conditions for view update Hinze / Scholz

88 SQLSQL // DML:DML: RemarksRemarks aboutabout NULLNULL

NULL treated as "unknown" Predicates: ƒ NULL AND TRUE = NULL ƒ NULL OR TRUE = TRUE ƒ predicate evaluates to NULL for row r → r not returned

Arithmetical expression: ƒ If NULL involved → expression evaluates to NULL



FU-Berlin, DBS I 2006, FU-Berlin, DBS Aggregates: ƒ Count(*) counts also NULL ƒ avg(*) ≠ sum(*)/count(*) Hinze / Scholz

89 SQLSQL // DML:DML: SummarySummary

SQL as Data manipulation language ƒ Declarative language ƒ Relational complete query language

Important terms and concepts: ƒ Insert, update, delete data ƒ Basic query pattern ƒ DISTINCT, ALL ƒ Set combination (UNION, INTERSECT, EXCEPT) ƒ Joins FU-Berlin, DBS I 2006, FU-Berlin, DBS ƒ Sub-queries (IN, EXISTSSOME, ALL) ƒ Aggregate functions ƒ GROUP BY, HAVING Hinze / Scholz ƒ View, view updates

90