1、第四章 SQL引言 IBM SYSTEM R SEQUEL ANSI 标准 SQL 1990 ISO 标准 SQL 1992 SQL3 (SQL99)体系结构 View Table File SQL DDL 包括完整性与安全性 DML SQL DDL 需要创建的结构 Table View IndexCreate table,view,index E.g.Create Table DEPT(DEPT#Number,DNAME Char(5),Budget Number(7,2);SQL DDL 续 索引 Create index on ()E.g.Create index I1 on EMP(E
2、#);Create index I2 on EMP(Ename);唯一性索引 E.g.Create unique index I1 on EMP(E#);SQL DDL 续 聚集索引 元组按照索引值顺序，物理上尽可能的存储在一起,在索引值上执行扫描（scan）操作时可以减少 I/O.E.g.Create cluster index CI1 on EMP(E#);基本查询块 典型的 SQL 查询语句格式:select A1,A2,.,Anfrom r1,r2,.,rmwhere PAis 代表属性ris 代表关系P 是谓词.Select 子句 select 短语用于列出所有要查询的结果属性.例如
3、查找 DEPT 关系中所有部门名字select dnamefrom DEPT 注意:SQL 大小写无关Select 子句-续 SQL 的查询结果中允许有重复.使用 distinct 消重复.例如：查找 DEPT 关系中所有不同名的部门名字select distinct dnamefrom DEPTSelect 子句-续 select 短语中可以包含 数学表达式.例如:select S#,Sname,Status 2from S.Where 子句 where 短语由给出谓词，其谓词由出现在短语由给出谓词，其谓词由出现在from 短语中的关系的属性组成短语中的关系的属性组成.查找所有居住在 Lon
4、don 并且状态大于 20的供应商的供应商号select S#from Swhere city=London AND status 20 比较操作结果可以用逻辑操作 and,or,和和 not相连相连.Where 子句-续 between 比较操作.查找状态在 20 和 30 之间的供应商的商号(也就是说要,20 并且 30)select S#from S where status between 20 and 30From 子句 from 短语列出的关系在执行时要被扫描短语列出的关系在执行时要被扫描.查找 employee department的结果 select from EMP,DEPT
5、 where emp.D#=dept.D#重命名操作 SQL 使用别名（alias name）对关系和属性重命名:old-name new-name 查找所有供应商的名字、商号和状态;将 S#重命名为 number、将 sname 重命名为 nameselect sname name,s#number,statusfrom S元组变量 from 短语使用别名定义元组变量.查找所有已供应零件的供应商名字和零件号.select sx.sname,spx.P#from S sx,SP Spx where sx.S#=spx.s#串操作 SQL 含有串匹配操作.末拌有两个特殊的符号描述:%.代表任意长
6、的子串._.代表任意的单字符.Find the names of all suppliers whose city name includes the substring“Main”.select snamefrom s where city like%Main%串操作-续 SQL 包括其他串操作例如 concatenation(using“|”)converting from upper to lower case(and vice versa)finding string length,extracting substrings,etc.排序 List in alphabetic orde
7、r the names of all suppliers locating in London cityselect distinct snamefrom Swhere city=Londonorder by sname desc 表示降序，asc 表示升序；缺省时升序 E.g.order by sname desc集合操作 union,intersect,和 except 集合操作自动消重复集合操作自动消重复集合操作-续 Find all cities where have a supplier,a part,or both:(select city from S)union(select
8、city from P)Find all cities where have both a supplier and a part.(select city from S)intersect(select city from P)Find all cities where have a supplier but no P.(select city from S)except(select city from P)聚集函数 avg min max sum count聚集函数-续 Find the average QTY that is supplied by supplier s1.select
9、 avg(QTY)from SP where s#=s1 Find the number of tuples in the supplier relation.select count(*)from S Find the number of suppliers who supply part.select count(distinct s#)from SP聚集函数-续 Find the number of part for each supplier.select sname,count(distinct p#)from S,SPwhere S.s#=SP.s#group by sname注意
10、:select 短语中出现在聚集函数外面的属性必须要在 group by 列表中聚集函数-续 Find the number of all suppliers who have supplied part more than 600.select s#,avg(QTY)from SPgroup by s#having avg(QTY)600聚集函数-续 Note:having 短语 和 where短语的不同处 select d#,avg(SAL)from EMP where age 600空值 元组的某些属性有可能取空值,记为 null null 表示一个未知的值或者表示一个不存在的值.任何涉
11、及 null 的算术运算的结果是 null E.g.5+null returns null 聚集函数计算中将忽略空值空值-续 is null 谓词用于判断空值.E.g.Find all Employee number which appear in the EMP relation with null values for d#.select E#from EMPwhere d#is null 任何与 null 的比较运算结果是 unknown E.g.5 null or null null or null=null空值-续 Total all part quantityselect sum(
12、QTY)from SP 上述语句忽略空值 QTY 如果没有非空的 QTY，结果是null 除了 count(*)，所有聚集函数计算都忽略 null values.嵌套子查询 SQL provides a mechanism for the nesting of subqueries.A subquery is a select-from-where expression that is nested within another query.A common use of subqueries is to perform tests for set membership,set compari
13、sons,and set cardinality.举例 Find all employees who have worked in sales department.select distinct Enamefrom EMPwhere d#in (select d#from DEPT where Dname=sale)集合比较 Find all employees whose salary greater than some managers salary.select Enamefrom EMPwhere sal some(select sal from EMP where E#in(sel
14、ect mgr from DEPT)集合比较-续 Find the names of all employees whose salary greater than all managers salary.select Enamefrom EMPwhere sal all(select sal from EMPwhere E#in(select mgr from DEPT)集合比较-续 Definition of set comparison F some r t r s.t.(F t)F all r t r(F t)Where can be:集合比较-续056(5 some)=true050
15、)=false505(5 some)=true(since 0 5)(read:5 some tuple in the relation)(5 some)=true(5=some (=some)in However,(some)not in集合比较-续056(5 all)=false6104)=true546(5 all)=true(since 5 4 and 5 6)(5=5000)删除 Delete all suppliers who are in Londondelete from Swhere city=London Delete all suppliers who supply pa
16、rt p2.delete from Swhere s#in(select s#from SP where p#=p2)Note:Here has some problem with constraints that will explained in Chapter 8 Delete the record of all employees with salary below the average.delete from EMPwhere SAL 4000update EMPset SAL=SAL 1.05where SAL 4000 The order is important更多举例 Fi
17、nd all employees who have the lowest salary in each department.Select Ename,d#,SAL From EMP Where SAL in(Select min(SAL)From EMP Group By d#)Note:Above statement has error,the correct is:Select Ename,d#,SAL From EMP Where(d#,SAL)in(Select d#,min(SAL)From EMP Group By d#)更多举例-续 Find all part number a
18、nd its total quantity Select p#,sum(QTY)totqty From SP Group By p#;or equivalently Select p#,(Select sum(QTY)From SP Where SP.p#=P.p#)totqty From P;嵌入 SQL The SQL standard defines embeddings of SQL in a variety of programming languages such as Pascal,PL/I,Fortran,C,and Cobol.A language to which SQL
19、queries are embedded is referred to as a host language,and the SQL structures permitted in the host language comprise embedded SQL.嵌入 SQL-续 The basic form of these languages follows that of the System R embedding of SQL into PL/I.EXEC SQL statement is used to identify embedded SQL request to the pre
20、processorEXEC SQL Note:this varies by language.E.g.the Java embedding uses#SQL .;嵌入 SQL-续 Query single tuple EXEC SQL Select Ename INTO:ename From EMP Where e#=e1 Query set tuples There are dismached problem between host language with sub-language,using middle relation to solve this question.Note:“:
21、ename”called host variable which need declared by special statement.嵌入 SQL-续EXEC SQL BEGIN DECLARE SECTION;Char SQLSTATE6;Char P#6;int Weight;EXEC SQL END DECLARE SECTION;P#=P2;EXEC SQL Select P.weight INTO :weight FROM P WHERE P.P#=:P#;If SQLSTATE=00000Then.Else.;嵌入 SQL-续 The statement for SQLSTATE
22、 EXEC SQL WHENEVER Conditon Not found no data was found 02000 Sqlerror an error occurred 举例 Specify the query in SQL and declare a cursor for itEXEC SQLdeclare c cursor for select sname,cityfrom S,SP where S.s#=SP.s#and SP.QTY :amountFrom within a host language,find the names and cities of suppliers
23、 supply more than the variable amount quantity part.嵌入 SQL-续 The open statement causes the query to be evaluatedEXEC SQL open c The fetch statement causes the values of one tuple in the query result to be placed on host language variables.EXEC SQL fetch c into:cn,:cc Repeated calls to fetch get succ
24、essive tuples in the query result嵌入 SQL-续 A variable called SQLSTATE in the SQL communication area(SQLCA)gets set to 02000 to indicate no more data is available The close statement causes the database system to delete the temporary relation that holds the result of the query.EXEC SQL close cNote:abo
25、ve details vary with language.E.g.the Java embedding defines Java iterators to step through result tuples.游标更新nCan update tuples fetched by cursor by declaring that the cursor is for update declare c cursor for select *from EMP where city=Parise for updatenTo update tuple at the current location of
26、cursor update EMP set SAL=SAL+100 where current of c动态 SQL Allows programs to construct and submit SQL queries at run time.The dynamic SQL program contains a?,which is a place holder for a value that is provided when the SQL program is executed.动态 SQL-续 Example of the use of dynamic SQL from within
27、a C program.char*sqlprog=“update EMP set SAL=SAL*1.05 where d#=?”EXEC SQL prepare dynprog from:sqlprog;char account 10=“A-101”;EXEC SQL execute dynprog using:account;ODBC Open DataBase Connectivity(ODBC)standard standard for application program to communicate with a database server.application progr
28、am interface(API)to open a connection with a database,send queries and updates,get back results.Applications such as GUI,spreadsheets,etc.can use ODBCODBC -续 Each database system supporting ODBC provides a driver library that must be linked with the client program.When client program makes an ODBC A
29、PI call,the code in the library communicates with the server to carry out the requested action,and fetch results.ODBC program first allocates an SQL environment,then a database connection handle.ODBC -续 Opens database connection using SQLConnect().Parameters for SQLConnect:connection handle,the serv
30、er to which to connect the user identifier,password Must also specify types of arguments:SQL_NTS denotes previous argument is a null-terminated string.ODBC 编程int ODBCexample()RETCODE error;HENV env;/*environment*/HDBC conn;/*database connection*/SQLAllocEnv(&env);SQLAllocConnect(env,&conn);SQLConnec
31、t(conn,aura.bell-,SQL_NTS,avi,SQL_NTS,avipasswd,SQL_NTS);.Do actual work SQLDisconnect(conn);SQLFreeConnect(conn);SQLFreeEnv(env);ExerciseWrite the following queries,based on the following database exampleMovie(title,year,length,inColor,studioName,producerC#)StarsIn(movieTitle,movieYear,strName)Movi
32、eStar(name,address,gender,birthdate)MovieExec(name,address,cert#,netWorth)Studio(name,address,presC#)Classes(class,type,country,numGuns,bore,displacement)Ships(name,class,launched)Battles(name,date)Outcomes(ship,battle,result)In SQL.1.Find Sandra Bullocks birthdate 2.Find all executives worth at lea
33、st$10,000,000 3.Find all the stars who either are male or live in Malibu 4.Which stars appeared in movies produced by MGM in 1995?5.Who is the president of MGM studio?6.Find the countries whose ships had the largest number of guns.7.Find the names of the ship with 16-inch bore.8.Find the average number of guns of battleship classes.
