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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
2、I1 on EMP (E#); 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
3、子句select 短语用于列出所有要查询的结果属性. 例如查找 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
4、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 London 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 employ
5、ee department的结果 select from EMP, DEPT 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
6、.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 leng
7、th, extracting substrings, etc.排序 List in alphabetic order the names of all suppliers locating in London cityselect distinct snamefrom Swhere city=Londonorder by snamedesc 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
8、a supplier, a part, or both:(select city from S)union(select 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-
9、续 Find the average QTY that is supplied by supplier s1. select avg (QTY) from SP where s#= s1Find the number of tuples in the supplier relation. select count (*) from SFind 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.sel
10、ect sname, count (distinct p#)from S, SPwhere S.s# = SP.s#group by sname注意: 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#, a
11、vg (SAL)from EMP where age 600空值 元组的某些属性有可能取空值, 记为 nullnull 表示一个未知的值或者表示一个不存在的值. 任何涉及 null 的算术运算的结果是 nullE.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
12、结果是 unknownE.g. 5 null or null null or null = null空值-续 Total all part quantityselect sum (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 a
13、nother query.A common use of subqueries is to perform tests for set membership, set comparisons, 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 t
14、han some managers salary .select Enamefrom EMPwhere sal some (select sal from EMP where E# in ( select 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 D
15、efinition 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) = 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
16、(since 5 4 and 5 6)(5= 5000)删除Delete all suppliers who are in Londondelete from Swhere city = LondonDelete all suppliers who supply part 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
17、employees with salary below the average .delete from EMPwhere SAL 4000update EMPset SAL = SAL 1.05where SAL 4000The order is important更多举例 Find 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 s
18、tatement 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 and 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#) totqt
19、y From P;嵌入 SQLThe 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 queries are embedded is referred to as a host language, and the SQL structures permitted in the host language comprise embedded SQL.嵌入 S
20、QL-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 preprocessorEXEC SQL Note: this varies by language. E.g. the Java embedding uses # SQL . ; 嵌入 SQL-续 Query single tuple EXEC SQL Select Ena
21、me 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: “:ename” called host variable which need declared by special statement. 嵌入 SQL-续EXEC SQL BEGIN DECLARE SECTION; Char SQLSTATE
22、6; 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 EXEC SQL WHENEVER ConditonNot found no data was found 02000Sqlerror an error occurred 举例Specify the query in SQL a
23、nd 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 supply more than the variable amount quantity part.嵌入 SQL-续The open statement causes the query to be evaluatedE
24、XEC 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 successive tuples in the query result嵌入 SQL-续 A variable called SQLSTATE in the SQL communication area (SQLCA) get
25、s set to 02000 to indicate no more data is availableThe close statement causes the database system to delete the temporary relation that holds the result of the query.EXEC SQL close cNote: above details vary with language. E.g. the Java embedding defines Java iterators to step through result tuples.
26、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 cursor update EMP set SAL = SAL + 100 where current of c动态 SQL Allows programs to construct and submit
27、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 a C program.char * sqlprog = “update EMP set SAL = SAL * where d# = ?”EXEC SQL prepare dynprog f
28、rom :sqlprog; char account 10 = “A-101”;EXEC SQL execute dynprog using :account;ODBCOpen DataBase Connectivity(ODBC) standard standard for application program to communicate with a database server.application program interface (API) to open a connection with a database, send queries and updates, get
29、 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 API call, the code in the library communicates with the server to carry out the
30、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 server to which to connectthe user identifier, password Must also specify type
31、s 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); SQLConnect(conn, aura.bell-, SQL_NTS, avi, SQL_NTS, avipasswd, SQL_NTS
32、); . 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) MovieStar(name, address, gender, birthdate)
33、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 least $10,000,00
34、0 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.
