1、Chapter 4: Advanced SQLChapter 4: Advanced SQLSQL Data Types and SchemasIntegrity Constraints AuthorizationEmbedded SQLDynamic SQLFunctions and Procedural Constructs*Recursive Queries*Advanced SQL Features*Built-in Data Types in SQL date: Dates, containing a (4 digit) year, month and dateExample: da

2、te 2005-7-27time: Time of day, in hours, minutes and seconds.Example: time 09:00:30 time 09:00:30.75timestamp: date plus time of dayExample: timestamp 2005-7-27 09:00:30.75interval: period of timeExample: interval 1 daySubtracting a date/time/timestamp value from another gives an interval valueInter

3、val values can be added to date/time/timestamp valuesBuild-in Data Types in SQL (Cont.)Can extract values of individual fields from date/time/timestampExample: extract (year from r.starttime) Can cast string types to date/time/timestamp Example: cast as dateExample: cast as timeUser-Defined Typescre

4、ate type construct in SQL creates user-defined typecreate type Dollars as numeric (12,2) final create domain construct in SQL-92 creates user-defined domain typescreate domain person_name char(20) not nullTypes and domains are similar. Domains can have constraints, such as not null, specified on the

5、m.Domain ConstraintsDomain constraints are the most elementary form of integrity constraint. They test values inserted in the database, and test queries to ensure that the comparisons make sense. New domains can be created from existing data typesExample:create domain Dollars numeric(12, 2) create d

6、omain Pounds numeric(12,2)We cannot assign or compare a value of type Dollars to a value of type Pounds. However, we can convert type as below (cast r.A as Pounds) (Should also multiply by the dollar-to-pound conversion-rate)Large-Object TypesLarge objects (photos, videos, CAD files, etc.) are store

7、d as a large object:blob: binary large object - object is a large collection of uninterpreted binary data (whose interpretation is left to an application outside of the database system)clob: character large object - object is a large collection of character dataWhen a query returns a large object, a

8、 pointer is returned rather than the large object itself.Integrity ConstraintsIntegrity constraints guard against accidental damage 意外破壞 to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency. A checking account must have a balance greater th

9、an $10,000.00A salary of a bank employee must be at least $4.00 an hourA customer must have a (non-null) phone number Constraints on a Single Relation not nullprimary keyuniquecheck (P ), where P is a predicateNot Null Constraint Declare branch_name for branch is not null branch_name char(15) not nu

10、llDeclare the domain Dollars to be not null create domain Dollars numeric(12,2) not nullThe Unique Constraintunique ( A1, A2, , Am)The unique specification states that the attributes A1, A2, AmForm a candidate key.Candidate keys are permitted to be non null (in contrastto primary keys).The check cla

11、usecheck (P ), where P is a predicateExample: Declare branch_name as the primary key for branch and ensure that the values of assets are non-negative.create table branch (branch_name char(15), branch_city char(30), assets integer, primary key (branch_name), check (assets = 0)The check clause (Cont.)

12、The check clause in SQL-92 permits domains to be restricted:Use check clause to ensure that an hourly_wage domain allows only values greater than a specified value.create domain hourly_wage numeric(5,2)constraint value_test check(value = 4.00)The domain has a constraint that ensures that the hourly_

13、wage is greater than 4.00The clause constraint value_test is optional; useful to indicate which constraint an update violated.Referential Integrity參照完整性Ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation.Exa

14、mple: If “Perryridge” is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”.Primary and candidate keys and foreign keys can be specified as part of the SQL create table statement:The primary key clause lists

15、attributes that comprise the primary key.The unique key clause lists attributes that comprise a candidate key.The foreign key clause lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key. By default, a foreign key references the primary key att

16、ributes of the referenced table.Referential Integrity in SQL Examplecreate table customer(customer_namechar(20),customer_streetchar(30),customer_citychar(30),primary key (customer_name )create table branch(branch_namechar(15),branch_citychar(30),assetsnumeric(12,2),primary key (branch_name )Referent

17、ial Integrity in SQL Example (Cont.)create table account(account_numberchar(10),branch_namechar(15),balanceinteger,primary key (account_number), foreign key (branch_name) references branch )create table depositor(customer_namechar(20),account_numberchar(10),primary key (customer_name, account_number

18、),foreign key (account_number ) references account,foreign key (customer_name ) references customer )AssertionsAn assertion is a predicate expressing a condition that we wish the database always to satisfy.An assertion in SQL takes the formcreate assertion check When an assertion is made, the system

19、 tests it for validity, and tests it again on every update that may violate the assertionThis testing may introduce a significant amount of overhead; hence assertions should be used with great care. SQL does not support quantifier “any” “all” directly Assertion ExampleEvery loan has at least one bor

20、rower who maintains an account with a minimum balance or $1000.00 create assertion balance_constraint check (not exists ( select * from loan where not exists ( select * from borrower, depositor, account where loan.loan_number = borrower.loan_number and borrower.customer_name = depositor.customer_nam

21、e and depositor.account_number = account.account_number and account.balance = 1000)Assertion ExampleThe sum of all loan amounts for each branch must be less than the sum of all account balances at the branch. create assertion sum_constraint check (not exists (select * from branch where (select sum(a

22、mount ) from loan where loan.branch_name = branch.branch_name ) = (select sum (amount ) from account where loan.branch_name = branch.branch_name )AuthorizationForms of authorization on parts of the database:Read - allows reading, but not modification of data.Insert - allows insertion of new data, bu

23、t not modification of existing data.Update - allows modification, but not deletion of data.Delete - allows deletion of data.Forms of authorization to modify the database schema (covered in Chapter 8):Index - allows creation and deletion of indices.Resources - allows creation of new relations.Alterat

24、ion - allows addition or deletion of attributes in a relation.Drop - allows deletion of relations.Authorization Specification in SQLThe grant statement is used to confer authorizationgrant on to is:a user-idpublic, which allows all valid users the privilege grantedA role (more on this in Chapter 8)G

25、ranting a privilege on a view does not imply granting any privileges on the underlying relations.The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).Privileges in SQLselect: allows read access to relation,or the ability to query using

26、 the viewExample: grant users U1, U2, and U3 select authorization on the branch relation:grant select on branch to U1, U2, U3insert: the ability to insert tuplesupdate: the ability to update using the SQL update statementdelete: the ability to delete tuples.all privileges: used as a short form for a

27、ll the allowable privilegesmore in Chapter 8Revoking Authorization in SQLThe revoke statement is used to revoke authorization.revoke on from Example:revoke select on branch from U1, U2, U3 may be all to revoke all privileges the revokee may hold.If includes public, all users lose the privilege excep

28、t those granted it explicitly.If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation.All privileges that depend on the privilege being revoked are also revoked.Embedded SQLThe SQL standard defines embeddings of SQL in a

29、variety of programming languages such as C, Java, 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.The basic form of these languages follows that of the System R embedding of SQL into

30、 PL/I.EXEC SQL statement is used to identify embedded SQL request to the preprocessorEXEC SQL END_EXECNote: this varies by language (for example, the Java embedding uses # SQL . ; ) Example QuerySpecify the query in SQL and declare a cursor 游標(biāo) for it EXEC SQL declare c cursor for select customer_nam

31、e, customer_city from depositor, customer, account where depositor.customer_name = customer.customer_name and depositor account_number = account.account_numberand account.balance :amount END_EXECFrom within a host language, find the names and cities of customers with more than the variable amount do

32、llars in some account.Embedded SQL (Cont.)The open statement causes the query to be evaluatedEXEC SQL open c END_EXECThe 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 END_EXECRepeated calls to fetch get succe

33、ssive tuples in the query resultA variable called SQLSTATE in the SQL communication area (SQLCA) gets 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 c END_EXECNote: ab

34、ove details vary with language. For example, the Java embedding defines Java iterators to step through result tuples.Updates Through CursorsCan update tuples fetched by cursor by declaring that the cursor is for update declare c cursor for select * from account where branch_name = Perryridge for upd

35、ateTo update tuple at the current location of cursor c update account set balance = balance + 100 where current of cDynamic SQLAllows programs to construct and submit SQL queries at run time.Example of the use of dynamic SQL from within a C program.char * sqlprog = “update account set balance = bala

36、nce * 1.05 where account_number = ?”EXEC SQL prepare dynprog from :sqlprog;char account 10 = “A-101”;EXEC SQL execute dynprog using :account;The dynamic SQL program contains a ?, which is a place holder for a value that is provided when the SQL program is executed.ODBC and JDBCAPI (application-progr

37、am interface) for a program to interact with a database serverApplication makes calls toConnect with the database serverSend SQL commands to the database serverFetch tuples of result one-by-one into program variablesODBC (Open Database Connectivity) works with C, C+, C#, and Visual BasicJDBC (Java D

38、atabase Connectivity) works with JavaODBCOpen 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 back results.Applications such as GUI, spr

39、eadsheets, etc. can use ODBCODBC (Cont.)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 requested action, and fetch results.ODB

40、C program first allocates an SQL environment, then a database connection handle.Opens database connection using SQLConnect(). Parameters for SQLConnect:connection handle,the server to which to connectthe user identifier, password Must also specify types of arguments:SQL_NTS denotes previous argument

41、 is a null-terminated string.ODBC Codeint ODBCexample() RETCODE error; HENV env; /* environment */ HDBC conn; /* database connection */ SQLAllocEnv(&env); SQLAllocConnect(env, &conn); SQLConnect(conn, , SQL_NTS, avi, SQL_NTS, avipasswd, SQL_NTS); . Do actual work SQLDisconnect(conn); SQLFreeConnect(

42、conn); SQLFreeEnv(env); ODBC Code (Cont.)Program sends SQL commands to the database by using SQLExecDirectResult tuples are fetched using SQLFetch()SQLBindCol() binds C language variables to attributes of the query result When a tuple is fetched, its attribute values are automatically stored in corr

43、esponding C variables.Arguments to SQLBindCol()ODBC stmt variable, attribute position in query resultThe type conversion from SQL to C. The address of the variable. For variable-length types like character arrays, The maximum length of the variable Location to store actual length when a tuple is fet

44、ched.Note: A negative value returned for the length field indicates null valueGood programming requires checking results of every function call for errors; we have omitted most checks for brevity.ODBC Code (Cont.)Main body of program char branchname80;float balance;int lenOut1, lenOut2;HSTMT stmt; S

45、QLAllocStmt(conn, &stmt);char * sqlquery = select branch_name, sum (balance) from account group by branch_name; error = SQLExecDirect(stmt, sqlquery, SQL_NTS); if (error = SQL_SUCCESS) SQLBindCol(stmt, 1, SQL_C_CHAR, branchname , 80, &lenOut1); SQLBindCol(stmt, 2, SQL_C_FLOAT, &balance, 0 , &lenOut2

46、); while (SQLFetch(stmt) = SQL_SUCCESS) printf ( %s %gn, branchname, balance); SQLFreeStmt(stmt, SQL_DROP); More ODBC FeaturesPrepared StatementSQL statement prepared: compiled at the databaseCan have placeholders: E.g. insert into account values(?,?,?)Repeatedly executed with actual values for the

47、placeholdersMetadata featuresfinding all the relations in the database andfinding the names and types of columns of a query result or a relation in the database.By default, each SQL statement is treated as a separate transaction that is committed automatically.Can turn off automatic commit on a conn

48、ectionSQLSetConnectOption(conn, SQL_AUTOCOMMIT, 0) transactions must then be committed or rolled back explicitly by SQLTransact(conn, SQL_COMMIT) orSQLTransact(conn, SQL_ROLLBACK)ODBC Conformance LevelsConformance levels specify subsets of the functionality defined by the standard.CoreLevel 1 requir

49、es support for metadata queryingLevel 2 requires ability to send and retrieve arrays of parameter values and more detailed catalog information.SQL Call Level Interface (CLI) standard similar to ODBC interface, but with some minor differences.JDBC 自學(xué)JDBC is a Java API for communicating with database

50、systems supporting SQLJDBC supports a variety of features for querying and updating data, and for retrieving query resultsJDBC also supports metadata retrieval, such as querying about relations present in the database and the names and types of relation attributesModel for communicating with the dat

51、abase:Open a connectionCreate a “statement” objectExecute queries using the Statement object to send queries and fetch resultsException mechanism to handle errorsJDBC Codepublic static void JDBCexample(String dbid, String userid, String passwd) try Class.forName (oracle.jdbc.driver.OracleDriver); Co

52、nnection conn = DriverManager.getConnection( jdbc:oracle:thin:2000:bankdb, userid, passwd); Statement stmt = conn.createStatement(); Do Actual Work . stmt.close(); conn.close(); catch (SQLException sqle) System.out.println(SQLException : + sqle); JDBC Code (Cont.)Update to databasetry stmt.executeUp

53、date( insert into account values (A-9732, Perryridge, 1200); catch (SQLException sqle) System.out.println(Could not insert tuple. + sqle);Execute query and fetch and print results ResultSet rset = stmt.executeQuery( select branch_name, avg(balance) from account group by branch_name);while (rset.next

54、() System.out.println( rset.getString(branch_name) + + rset.getFloat(2);JDBC Code Details Getting result fields:rs.getString(“branchname”) and rs.getString(1) equivalent if branchname is the first argument of select result.Dealing with Null valuesint a = rs.getInt(“a”);if (rs.wasNull() Systems.out.p

55、rintln(“Got null value”);Procedural Extensions and Stored ProceduresSQL provides a module language Permits definition of procedures in SQL, with if-then-else statements, for and while loops, etc.more in Chapter 9Stored ProceduresCan store procedures in the database then execute them using the call s

56、tatementpermit external applications to operate on the database without knowing about internal detailsThese features are covered in Chapter 9 (Object Relational Databases)Functions and Procedures（自學(xué)）SQL:1999 supports functions and proceduresFunctions/procedures can be written in SQL itself, or in an

57、 external programming languageFunctions are particularly useful with specialized data types such as images and geometric objectsExample: functions to check if polygons overlap, or to compare images for similaritySome database systems support table-valued functions, which can return a relation as a r

58、esultSQL:1999 also supports a rich set of imperative constructs, includingLoops, if-then-else, assignmentMany databases have proprietary procedural extensions to SQL that differ from SQL:1999SQL FunctionsDefine a function that, given the name of a customer, returns the count of the number of account

59、s owned by the customer. create function account_count (customer_name varchar(20) returns integer begin declare a_count integer; select count (* ) into a_count from depositor where depositor.customer_name = customer_name return a_count; endFind the name and address of each customer that has more tha

60、n one account.select customer_name, customer_street, customer_cityfrom customerwhere account_count (customer_name ) 1Table FunctionsSQL:2003 added functions that return a relation as a resultExample: Return all accounts owned by a given customercreate function accounts_of (customer_name char(20)retu