Database Technology. Topic 3: SQL. Structured Query Language. Creating Tables SQL DDL. Creating Tables (Example) Modifying Table Definitions

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1 Structured Query Language eclarative language (what data to get, not how) onsidered one of the major reasons for the commercial success of relational databases Statements for data definitions, queries, and updates oth L and ML Terminology: Olaf Hartig olaf.hartig@liu.se Relational Model SQL relation table tuple row attribute column Syntax notes: Some interfaces require each statement to end with a semicolon SQL is not case-sensitive 2 reating Tables RETE TLE <tablename> ( <colname> <datatype> [<constraint>],, [<constraint>], ); SQL L ata types: integer, decimal, number, varchar, char, etc. onstraints: not, primary key, foreign key, unique, etc. reating Tables (Example) Modifying Table efinitions RETE TLE ORKS_ON ( ESSN integer, PNO integer, HOURS decimal(3,), dd, delete, and modify columns and constraints LTER TLE EMPLOEE OLUMN JO VRHR(2); LTER TLE EMPLOEE ROP OLUMN RESS SE; constraint pk_workson primary key (ESSN, PNO), LTER TLE ORKS_ON ROP FOREIGN KE fk_works_emp; LTER TLE ORKS_ON ONSTRINT fk_works_emp FOREIGN KE (ESSN) REFERENES EMPLOEE(SSN); constraint fk_works_emp FOREIGN KE (ESSN) references EMPLOEE(SSN), constraint fk_works_proj FOREIGN KE (PNO) references PROJET(PNUMER) ); elete a table and its definition ROP TLE EMPLOEE; 6

2 asic SQL Retrieval Queries ll retrievals use SELET statement: SELET <return list> FROM <table list> [ HERE <condition> ] ; SQL Queries where <return list> is a list of column names (or expressions) whose values are to be retrieved <table list> is a list of table names required to process the query <condition> is a oolean expression that identifies the tuples to be retrieved by the query (if no HERE clause, all tuples to be retrieved) Example SELET title, year, genre FROM Film HERE director = 'Steven Spielberg'. Start with the relation named in the FROM clause 3. For each remaining tuple, create a return tuple with columns for each expression (column name) in the SELET clause genre drama year director John ells minutes 0 Lincoln biography 202 Steven Spielberg 0 ar Horse drama 20 Steven Spielberg 6 rgo drama 202 en ffleck 20 budget List all information about the employees of department. or gross,000,000,39,063 6,000,000 8,08,67 66,000,000 79,883,39,00,000 3,78,2 SELET * HERE NO = ; 0 Pattern Matching in Strings List the last name, birth date and address for all employees whose name is `licia J. (assuming that table EMPLOEE has the attributes FNME, MINIT, LNME, TE, RESS, etc.) List the birth date and address for all employees whose last name contains the substring aya SELET TE, RESS HERE LNME LIKE %aya% ; SELET LNME, TE, RESS HERE FNME = licia N MINIT = J N LNME = ; Possible logical LIKE comparison operator % represents 0 or more characters _ represents a single character operators: and, or, not Possible comparison operators: =, <>, >, =>, etc. 9 Logical Operators ll ttributes SELET FNME, MINIT, LNME, SSN, TE, RESS, SE, SLR, SUPERSSN, NO HERE NO = ; 2. onsider each tuple one after the other, eliminating those that do not satisfy the HERE clause Film title The ompany Men 8 2

3 s Tables as Sets List all employees that do not have a boss. SELET SLR ; SQL considers a table as a multi-set (bag), i.e. tuples may occur more than once in a table This is different from the relational data model SUPERSSN = and SUPERSSN <> will not return any matching tuples, because is incomparable to any value, including another hy? List all employees and the names of their departments. SELET LNME, NME, EPRTMENT; EMPLOEE EPRTMENT NME Example: hich department managers have dependents? Show their SSN. NUM LNME M SELET MGRSSN FROM EPRTMENT INTERSET SELET ESSN FROM EPENENT; 6 Join: Equijoin NME 7 E Join: artesian Product NO E SELET FNME UNION SELET EPENENT_NME FROM EPENENT; Example: retrieve the first names of all people in the database. SLR List all salaries without duplicates SELET ISTINT SLR ; uplicate tuples are removed. Queries can be combined by set operations: UNION, INTERSET, EEPT (MySQL only supports UNION) List all salaries: LNME Set Operations SLR SELET SLR ; Removing duplicates is expensive User may want information about duplicates ggregation operators (e.g., sum) 3 Removing uplicates List all salaries: SELET FNME, LNME HERE SUPERSSN IS ; SLR Foreign key in EMPLOEE List all employees and the names of their departments. SELET LNME, NME, EPRTMENT HERE NO = NUM; Equijoin EMPLOEE LNME NO EPRTMENT NME NUM artesian product Primary key in EPRTMENT LNME NO NME NUM 8

4 Inner Join mbiguous Names: liasing List all employees and the names of their departments. SELET LNME, NME, EPRTMENT HERE NO = NUM; hat if the same attribute name is used in different relations? No alias hole name SELET EMPLOEE.NME, EPRTMENT.NME SELET NME, NME, EPRTMENT HERE NO=NUM;, EPRTMENT HERE EMPLOEE.NO=EPRTMENT.NUM; s an alternative, the join condition may be given in the FROM clause by using the keywords INNER JOIN and ON as follows: lias SELET E.NME,.NME E, EPRTMENT HERE E.NO=.NUM; SELET LNME, NME INNER JOIN EPRTMENT ON NO = NUM; Self-Join 9 20 Self-Joins may also be written as Inner Join List the last name for all employees together with the last names of their bosses SELET E.LNME S Employee, S.LNME S oss E, EMPLOEE S HERE E.SUPERSSN = S.SSN; Employee oss List the last name for all employees together with the last names of their bosses SELET E.LNME S Employee, S.LNME S oss E, EMPLOEE S HERE E.SUPERSSN = S.SSN; 22 artesian product SELET * FROM a, b; If there exist matching tuples in right table, works like inner join If no matching tuple in right table, one tuple in result with left tuple values padded with values for columns of right table custid name Lee illis Ng Harrison address 633 S. First King 23 Main Queen N. 808 Main Sale phone saleid date ec ec 9 ec ec 23 ec custid SELET * FROM ustomer LEFT JOIN Sale ON ustomer.custid = Sale.custid ustomer.custid name Lee illis illis Ng Harrison Joins Revisited Every tuple in left table appears in result ustomer SELET E.LNME Employee, S.LNME oss E INNER JOIN EMPLOEE S ON E.SUPERSSN = S.SSN; 2 Left Outer Join Employee oss address 633 S. First King King 23 Main Queen N. 808 Main Topic 3: SQL phone saleid date Sale.custid ec ec 9 ec ec Equijoin, inner join SELET * from, HERE =; 2 2 Thetajoin SELET * from, HERE >; 2 2 2

5 Joins Revisited (cont'd) Subqueries Right outer join SELET * FROM RIGHT JOIN on =; Full outer join ( union of right+left) SELET * FROM LEFT JOIN on =; Quiz SELET LNME, ORKS_ON HERE SSN = ESSN N HOURS <= 0.0; {>, >=, <, <=, <>} + {N, SOME, LL} SELET LNME HERE SSN NOT IN (SELET ESSN FROM ORKS_ON HERE HOURS > 0.0); Or EISTS SELET LNME HERE NOT EISTS (SELET * FROM ORKS_ON HERE SSN = ESSN N HOURS > 0.0); SELET * FROM FULL JOIN b on =; Left outer join List all employees that do not have any project assignment with more than 0 hours 2 ountry ode Name ismember ountry Organization 26 onsider the following two SQL queries: SELET Name FROM ountry HERE ode IN ( SELET ountry FROM IsMember HERE Organization = 'EU' ); dditional Features SELET Name FROM ountry, IsMember HERE ode = ountry N Organization = 'EU'; re these queries equivalent? (yes) (no) 27 Extended SELET Syntax ggregate Functions Used to accumulate information from multiple tuples, forming a single-tuple summary uilt-in aggregate functions: SUM, M, MIN, VG, OUNT SELET <attribute-list and function-list> FROM <table-list> [ HERE <condition> ] [ GROUP <grouping attribute-list>] [ HVING <group condition> ] [ ORER <attribute-list> ]; Example: hat is the average budget of all movies? SELET VG(budget) FROM Film; Used in the SELET clause and the HVING clause Hence, cannot be used in the HERE clause! values are not considered in the computations; e.g.,: 0 0 VG:

6 ggregate Functions (cont'd) Grouping efore ggregation Example How many movies were directed by Steven Spielberg? How can we answer a query such as How many films were directed by each director after? SELET OUNT(*) FROM Film HERE director='steven Spielberg'; ll tuples in the result are counted, with duplicates! i.e., OUNT(title) or OUNT(director) give same result OUNT(ISTINT year) would include each year only once Need to produce a result with one tuple per director.partition relation into subsets based on grouping column(s) 2.pply aggregate function to each such group independently 3.Produce one tuple per group 3 32 Grouping efore ggregation Filtering Out hole Groups How can we answer a query such as How many films were directed by each director after? fter partitioning into groups, whole partitions can be discarded i.e., HVING clause specifies a condition on the grouped tuples SELET NO, OUNT(*), VG(SLR) GROUP NO HVING OUNT(*) > 2; GROUP clause to specify grouping attributes SELET director, OUNT(*) FROM Film HERE year > GROUP director; Important: Every element in SELET clause must be a grouping column or an aggregation function. e.g., SELET director, year, OUNT(*) would not be allowed (in the query above) unless also grouping by year: i.e., GROUP director, year HVING clause cannot reference individual tuples within a group Instead, can reference grouping column(s) and aggregates only ontrast HERE clause to HVING clause Note: 33 s for aggregation, no GROUP clause means relation treated as one group Sorting Query Results Show the department names and their locations in alphabetical order SELET NME, LOTION FROM EPRTMENT, EPT_LOTIONS L HERE.NUMER = L.NUMER ORER NME S, LOTION ES; NME SQL ata Manipulation LOTION Stafford Houston Sugarland Houston ellaire 3 3

7 Inserting ata Updating ata INSERT INTO <table> (<attr>, ) VLUES ( <val>, ) ; INSERT INTO <table> (<attr>, ) <subquery> ; UPTE <table> SET <attr> = <val>, HERE <condition> ; UPTE <table> SET (<attr>,.) = ( <subquery> ) HERE <condition> ; Integrity constraint! Referential integrity constraint! Store information about how many hours an employee works for the project ' into ORKS_ON. INSERT INTO ORKS_ON VLUES (236789,, 32.); Give all employees in the department a 0% raise in salary UPTE EMPLOEE SET SLR = SLR*. HERE NO IN (SELET NUMER FROM EPRTMENT HERE NME = ); Integrity constraint! Referential integrity constraint! 37 eleting ata ELETE FROM <table> HERE <condition> ; elete the employees having the last name from the EMPLOEE table. ELETE Views HERE LNME = ; Foreign key EMPLOEE FNME M LNME SSN Ramesh K Joyce 333 hmad V James E EPRTMENT NME NUMER MGRSSN ON ELETE SET / EFULT / SE? Referential integrity constraint! 39 hat are Views? virtual table derived from other (possibly virtual) tables, i.e. always up-to-date RETE VIE dept_view S SELET NO, OUNT(*) S, VG(SLR) S S GROUP NO; hy? Simplify query commands data security Enhance programming productivity Provide 38