数据库原理PPT课件第三章.ppt

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1、4.2Database SystemnData DefinitionnBasic Query StructurenSet OperationsnAggregate FunctionsnNull ValuesnNested SubqueriesnComplex Queries nViewsnModification of the DatabasenJoined Relations* 4.3Database SystemnIBM Sequel language developed as part of System R project at the IBM San Jose Research La

2、boratorynRenamed Structured Query Language (SQL)nANSI and ISO standard SQL:lSQL-86lSQL-89lSQL-92 lSQL:1999 (language name became Y2K compliant!)lSQL:2003nCommercial systems offer most, if not all, SQL-92 features, plus varying feature sets from later standards and special proprietary features. lNot

3、all examples here may work on your particular system.4.4Database SystemnThe schema for each relation.nThe domain of values associated with each attribute.nIntegrity constraintsnThe set of indices to be maintained for each relations.nSecurity and authorization information for each relation.nThe physi

4、cal storage structure of each relation on disk.Allows the specification of not only a set of relations but also information about each relation, including:4.5Database Systemnchar(n). Fixed length character string, with user-specified length n.nvarchar(n). Variable length character strings, with user

5、-specified maximum length n. Nchar(n), nVarchar(n) (for unicode ,2byte code,1-4000 chars)nText. Variable length character strings,1 to 2GB.=varchar(max)nint. Integer (4B,a finite subset of the integers that is machine-dependent).nsmallint. Small integer (2B,a subset of the integer domain type).nBigi

6、nt. Big integer (8B),tinyint(1B),bit(多个位占多个位占1B)nnumeric(p,d). Fixed point number, with user-specified precision of p digits, with d digits to the right of decimal point. Decimal(p,d).4.6Database Systemnreal, double precision. Floating point and double-precision floating point numbers, with machine-

7、dependent precision.nfloat(n). Floating point number, with user-specified precision of at least n digits.nDatatime 8B:yyyy.mm.dd h:m:s,smalldatatime 4BnMoney 8BnXml (2GB)(不同表单可以存在不同表单可以存在xml类型的属性字段中类型的属性字段中)nBinary(n) 1-8000BnImage 2GBnTimestamp 8BnSql_variant 1200nComparison results can be combined

8、 using the logical connectives and, or, and not. nComparisons can be applied to results of arithmetic expressions.4.17Database SystemnSQL includes a between comparison operatornExample: Find the loan number of those loans with loan amounts between $90,000 and $100,000 (that is, $90,000 and $100,000)

9、 select loan_numberfrom loanwhere amount between 90000 and 100000 OR: where amount =90000 and amount S.assets and S.branch_city = Brooklyn nKeyword as is optional and may be omitted borrower as T borrower T select customer_name, T.loan_number, S.amount from borrower as T, loan as S where T.loan_numb

10、er = S.loan_number4.21Database SystemnSQL includes a string-matching operator for comparisons on character strings. The operator “like” uses patterns that are described using two special characters:lpercent (%). The % character matches any substring.lunderscore (_). The _ character matches any chara

11、cter.nFind the names of all customers whose street includes the substring “Main”.select customer_namefrom customerwhere customer_street like % Main% nMatch the name “Main%”like Main% escape nSQL supports a variety of string operations such aslconcatenation (using “|”)l converting from upper to lower

12、 case (and vice versa)l finding string length, extracting substrings, etc.4.22Database SystemnList in alphabetic order the names of all customers having a loan in Perryridge branchselect distinct customer_namefrom borrower, loanwhere borrower loan_number = loan.loan_number and branch_name = Perryrid

13、ge order by customer_name ascnWe may specify desc for descending order or asc for ascending order, for each attribute; ascending order is the default.lExample: order by customer_name desc4.23Database SystemnIn relations with duplicates, SQL can define how many copies of tuples appear in the result.n

14、Multiset versions of some of the relational algebra operators given multiset relations r1 and r2:1. (r1): If there are c1 copies of tuple t1 in r1, and t1 satisfies selections , then there are c1 copies of t1 in (r1).2. A (r ): For each copy of tuple t1 in r1, there is a copy of tuple A (t1) in A (r

15、1) where A (t1) denotes the projection of the single tuple t1.3. r1 x r2 : If there are c1 copies of tuple t1 in r1 and c2 copies of tuple t2 in r2, there are c1 x c2 copies of the tuple t1. t2 in r1 x r24.24Database SystemnExample: Suppose multiset relations r1 (A, B) and r2 (C) are as follows: r1

16、= (1, a) (2,a) r2 = (2), (3), (3)nThen B(r1) would be (a), (a), while B(r1) x r2 would be(a,2), (a,2), (a,3), (a,3), (a,3), (a,3)nSQL duplicate semantics: select A1, A2, ., Anfrom r1, r2, ., rmwhere Pis equivalent to the multiset version of the expression:)(21,21mPAAArrrn4.25Database SystemnThe set

17、operations union, intersect, and except operate on relations and correspond to the relational algebra operations nEach of the above operations automatically eliminates duplicates; to retain all duplicates use the corresponding multiset versions union all, intersect all and except all.Suppose a tuple

18、 occurs m times in r and n times in s, then, it occurs:lm + n times in r union all slmin(m,n) times in r intersect all slmax(0, m n) times in r except all s4.26Database SystemnFind all customers who have a loan, an account, or both:(select customer_name from depositor)except(select customer_name fro

19、m borrower)(select customer_name from depositor)intersect(select customer_name from borrower)n Find all customers who have an account but no loan.(select customer_name from depositor)union(select customer_name from borrower)n Find all customers who have both a loan and an account.4.27Database System

20、nThese functions operate on the multiset of values of a column of a relation, and return a valueavg: average valuemin: minimum valuemax: maximum valuesum: sum of valuescount: number of values4.28Database SystemnFind the average account balance at the Perryridge branch.n Find the number of depositors

21、 in the bank.n Find the number of tuples in the customer relation.select avg (balance)from accountwhere branch_name = Perryridge select count (*)from customerselect count (distinct customer_name)from depositorselect avg (distinct balance) 4.29Database SystemnFind the number of depositors for each br

22、anch.Note: Attributes in select clause outside of aggregate functions must appear in group by list(除聚集函数外，在除聚集函数外，在selectselect中出现的属性必须在中出现的属性必须在group bygroup by中出现中出现)（Group by branch_name,street -先按branch_name分组，在组内再按street分组）select branch_name, count (distinct customer_name)from depositor, accoun

23、twhere depositor.account_number = account.account_numbergroup by branch_name4.30Database SystemnFind the names of all branches where the average account balance is more than $1,200.Note: predicates in the having clause are applied after the formation of groups whereas predicates in the where clause

24、are applied before forming groups（where 条件作用于条件作用于 分组前，而分组前，而having条件作用于分组后，条件作用于分组后，即每组满足的条件）即每组满足的条件） select branch_name, avg (balance) from account group by branch_name having avg (balance) 12004.31Database System 使用使用GROUP BY子句可以按一定的条件对查询到子句可以按一定的条件对查询到的结果进行分组，再对每一组数据计算统计信息。的结果进行分组，再对每一组数据计算统计信息

25、。 SELECT column_name1, column_name2 ,.n FROM table_name WHERE search_condition GROUP BY group_by_expression HAVING search_condition GROUP BY将查询结果按将查询结果按 (group_by_expression)进行分组，该属性列相等的记录为一个组。进行分组，该属性列相等的记录为一个组。 通常，在每组中通过聚合函数来计算一个或者多通常，在每组中通过聚合函数来计算一个或者多个列。个列。 如果如果GROUP带有带有HAVING，则只有满足，则只有满足search_

26、condition的组才能输出。的组才能输出。GROUP BY与与HAVING子句子句4.32Database SystemSELECT attribute list - Output columns of result table FROM table list - Input tables WHERE selection-condition - Condition to filter out rows GROUP BY grouping attribute(s) - Grouping of rows with common - column values HAVING grouping c

27、ondition - Condition to filter out groups ORDER BY attribute ASC|DESCpairs - Ordering of rows in output （order by branch_name，assets -先按先按b_n排序，排序，b_n相等的再按相等的再按assets排）排）Notes:Notes:n Only the first two are mandatory; the rest are optionalOnly the first two are mandatory; the rest are optionaln The

28、order of the clauses cannot be changed. Optional clauses can be The order of the clauses cannot be changed. Optional clauses can be omitted. omitted. nFROM 最多可以指定最多可以指定16个表个表4.33Database SystemnIt is possible for tuples to have a null value, denoted by null, for some of their attributesnnull signifi

29、es an unknown value or that a value does not exist.nThe predicate is null can be used to check for null values.lExample: Find all loan number which appear in the loan relation with null values for amount.select loan_numberfrom loanwhere amount is nullnThe result of any arithmetic expression involvin

30、g null is nulllExample: 5 + null returns nullnHowever, aggregate functions simply ignore nullslMore on next slide4.34Database SystemnAny comparison with null returns unknownlExample: 5 null or null null or null = nullnThree-valued logic using the truth value unknown:lOR: (unknown or true) = true, (u

31、nknown or false) = unknown (unknown or unknown) = unknownlAND: (true and unknown) = unknown, (false and unknown) = false, (unknown and unknown) = unknownlNOT: (not unknown) = unknownl“P is unknown” evaluates to true if predicate P evaluates to unknownnResult of where clause predicate is treated as f

32、alse if it evaluates to unknown4.35Database SystemnTotal all loan amountsselect sum (amount )from loanlAbove statement ignores null amountslResult is null if there is no non-null amountnAll aggregate operations except count(*) ignore tuples with null values on the aggregated attributes.4.36Database

33、System例：统计有成绩的学生的人数例：统计有成绩的学生的人数 SELECT COUNT (SCORE) FROM SC -成绩为零的同学计算，没有成绩（即为空值）的不计成绩为零的同学计算，没有成绩（即为空值）的不计 SELECT COUNT(*) FROM S WHERE DEPT=计算机计算机注意：注意：COUNT（*）用来统计元组的个数。）用来统计元组的个数。此函数不消除重复行，也不允许使用此函数不消除重复行，也不允许使用DISTINCT关键字关键字4.37Database SystemnSQL provides a mechanism for the nesting of subqu

34、eries.nA subquery is a select-from-where expression that is nested within another query.nA common use of subqueries is to perform tests for set membership, set comparisons, and set cardinality.4.38Database SystemnFind all customers who have both an account and a loan at the bank.n Find all customers

35、 who have a loan at the bank but do not have an account at the bankselect distinct customer_namefrom borrowerwhere customer_name not in (select customer_name from depositor )select distinct customer_namefrom borrowerwhere customer_name in (select customer_name from depositor )4.39Database SystemnFin

36、d all customers who have both an account and a loan at the Perryridge branchn Note: Above query can be written in a much simpler manner. The formulation above is simply to illustrate SQL features.select distinct customer_namefrom borrower, loanwhere borrower.loan_number = loan.loan_number and branch

37、_name = Perryridge and (branch_name, customer_name ) in(select branch_name, customer_name from depositor, account where depositor.account_number = account.account_number )4.40Database SystemnFind all branches that have greater assets than some branch located in Brooklyn.n Same query using some claus

38、eselect branch_namefrom branchwhere assets some (select assets from branch where branch_city = Brooklyn) select distinct T.branch_namefrom branch as T, branch as S where T.assets S.assets and S.branch_city = Brooklyn 4.41Database SystemnF some r t r such that (F t )Where can be: 056(5 some) = true05

39、0) = false505(5 some) = true (since 0 5)(read: 5 some tuple in the relation) (5 all(select assetsfrom branchwhere branch_city = Brooklyn) 4.43Database SystemnF all r t r (F t)056(5 all) = false6104) = true546(5 all) = true (since 5 4 and 5 6)(5 1200Note that we do not need to use the having clause,

40、since we compute the temporary (view) relation branch_avg in the from clause, and the attributes of branch_avg can be used directly in the where clause.4.52Database System例：学生基本信息表例：学生基本信息表STUD_IDNAMEBIRTHDAYGENDERADDRESSTELCODEZIPCODEMARK0801010811张源张源12-05-1986男男北京市海淀区北京市海淀区010-6457234510008056008

41、01020201赵明赵明08-06-1986男男上海市浦东区上海市浦东区021-648972322017005600801030101王刚王刚01-02-1986男男天津市南开区天津市南开区022-835723363000005600801050201陈红陈红10-25-1986女女武汉市汉口区武汉市汉口区027-745653504300005600801040112孙强孙强06-07-1986男男重庆市沙坪坝重庆市沙坪坝023-823423484000005600801020103李伟李伟09-01-1986男男北京市大兴县北京市大兴县010-689029471026005600801010

42、634钱昆钱昆12-06-1986男男广州市海珠区广州市海珠区020-456724535100005600801030213郑芳郑芳08-09-1986女女江苏省南京市江苏省南京市025-845739412100005600801010102袁飞袁飞03-11-1986男男湖南省长沙县湖南省长沙县0731-45723454100005600801040123孔荣孔荣05-31-1986男男云南省昆明市云南省昆明市0871-26475356500006000801050127张军张军11-03-1987男男成都市和平区成都市和平区028-852495676100415700801010704王一

43、明王一明03-03-1986男男甘肃省兰州市甘肃省兰州市0621-22218375900005734.53Database System学生基本信息表结构学生基本信息表结构列名列名数据类型数据类型大小大小小数位小数位是否为空是否为空默认值默认值列名含义列名含义1STUD_IDchar10N0801010101学号学号2NAMEnvarchar4N姓名姓名3BIRTHDAYdatetime出生日期出生日期4GENDERnchar1性别性别5ADDRESSnvarchar20家庭地址家庭地址6TELCODEchar12电话电话7ZIPCODEchar6邮编邮编8MARKdecimal30560入学

44、成绩入学成绩4.54Database SystemUSE studentGOCREATE TABLE stud_info ( stud_id CHAR(10) NOT NULL, name NVARCHAR(4) NOT NULL, birthday DATETIME, gender NCHAR(1), address NVARCHAR(20), telcode CHAR(12), zipcode CHAR(6), mark DECIMAL(3,0) )4.55Database SystemCREATE TABLE teacher_info (teacher_id CHAR(6) NOT NU

45、LL, name NVARCHAR(4) NOT NULL, gender NCHAR(1), age INT, tech_title NVARCHAR(5), telephone VARCHAR(12), salary DECIMAL(7,2), course_id CHAR(10) );CREATE TABLE stud_grade(stud_id CHAR(10) NOT NULL, name NVARCHAR(4) NOT NULL, course_id CHAR(10), grade DECIMAL(4,1)4.56Database System简单查询语句简单查询语句(示例示例3.

46、1)4.57Database System简单查询语句简单查询语句(示例示例3.2)4.58Database SystemFROM子句子句(示例示例3.3)4.59Database System使用使用SELECTINTO语句可以在查询数据的基语句可以在查询数据的基础上创建新的数据表。通常，可使用这种方法来础上创建新的数据表。通常，可使用这种方法来创建临时表，以便在随后的开发过程中使用。创建临时表，以便在随后的开发过程中使用。SELECT column_name1, column_name2,.nINTO new_table FROM table_name其中，其中， new_table为新创

47、建的表名称，它在当前为新创建的表名称，它在当前数据库中是不存在的。数据库中是不存在的。4.60Database SystemINTO子句子句(示例示例3.4)4.61Database SystemWHERE子句中常用的查询条件包括：子句中常用的查询条件包括：比较，比较包括的运算符主要有比较，比较包括的运算符主要有、=、=、等；等；q 确定范围，包括确定范围，包括BETWEEN A AND B 与与NOT BETWEEN A AND B；q 确定集合，包括确定集合，包括IN、NOT IN等；等；q 字符匹配，包括字符匹配，包括LIKE、NOT LIKE；q 空值，包括空值，包括IS NULL、I

48、S NOT NULL；q 查询结果，查询结果，包括包括EXISTS、NOT EXISTS；q 多重条件，主要有多重条件，主要有AND、OR、NOT等。等。WHERE子句子句4.62Database SystemWHERE子句子句(示例示例3.5)4.63Database SystemWHERE子句子句(示例示例3.6)4.64Database SystemWHERE子句子句(示例示例3.7)4.65Database SystemWHERE子句子句(示例示例3.8)4.66Database SystemORDER BY子句子句(示例示例3.9)查询所有男生学号、姓名和查询所有男生学号、姓名和年龄

49、年龄，并按出生日期进行排列，并按出生日期进行排列(升序升序) 4.67Database SystemGROUP BY与与HAVING子句子句3.10统计软件院软件工程专业（院：学号中的统计软件院软件工程专业（院：学号中的3，4位，位，专业：专业：5,6位位=01 ）学生的平均入学成绩）学生的平均入学成绩4.68Database System在教师信息表中，按职称分组统计在教师信息表中，按职称分组统计“讲师讲师”的平均年龄的平均年龄USE studentGOSELECT tech_title, avg(age)FROM teacher_infoGROUP BY tech_titleHAVING

50、tech_title = N讲师讲师CREATE TABLE teacher_info (teacher_id CHAR(6) NOT NULL, name NVARCHAR(4) NOT NULL, tech_title NVARCHAR(5), salary DECIMAL(7,2), course_id CHAR(10) );4.69Database SystemSELECT column_name1, column_name2,.nFROM table_name WHERE search_conditionORDER BY column_nameASC | DESC, .COMPUTE