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Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Lecture 7 of 42
Friday, 08 September 2006
William H. Hsu Department of Computing and Information Sciences, KSU
KSOL course page: http://snipurl.com/va Course web site: http://www.kddresearch.org/Courses/Fall-2006/CIS Instructor home page: http://www.cis.ksu.edu/~bhsu
Reading for Next Class: Sections 4.5 – 4.6, p. 137 – 151, Silberschatz et al. , 5th^ edition MySQL Primer info (to be posted on Handouts page)
Embedded SQL and Dynamic SQL
Notes: Assertions, Authorization, Cursors
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Basic Query Structure:
Review
z SQL is based on set and relational operations with certain modifications and enhancements z A typical SQL query has the form:
select A 1 , A 2 , ..., An from r 1 , r 2 , ..., r (^) m where P
Ai represents an attribute Ri represents a relation P is a predicate. z This query is equivalent to the relational algebra expression.
z The result of an SQL query is a relation.
∏ A 1 , A 2 ,Κ, An ( σ P ( r 1 × r 2 ×Κ× rm ))
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Update of a View:
Review
Update of a View:
Review
z Create a view of all loan data in the loan relation, hiding the amount attribute create view branch_loan as select branch_name, loan_number from loan z Add a new tuple to branch_loan insert into branch_loan values (‘Perryridge’, ‘L-307’) This insertion must be represented by the insertion of the tuple (‘L-307’, ‘Perryridge’, null ) into the loan relation
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
AssertionsAssertions
z An assertion is a predicate expressing a condition that we wish the database always to satisfy. z An assertion in SQL takes the form create assertion <assertion-name> check z When an assertion is made, the system tests it for validity, and tests it again on every update that may violate the assertion This testing may introduce a significant amount of overhead; hence assertions should be used with great care. z Asserting for all X , P ( X ) is achieved in a round-about fashion using not exists X such that not P ( X )
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Authorization Authorization
Forms of authorization on parts of the database:
z Read - allows reading, but not modification of data. z Insert - allows insertion of new data, but not modification of existing data. z Update - allows modification, but not deletion of data. z Delete - allows deletion of data.
Forms of authorization to modify the database schema (covered in Chapter 8): z Index - allows creation and deletion of indices. z Resources - allows creation of new relations. z Alteration - allows addition or deletion of attributes in a relation. z Drop - allows deletion of relations.
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Authorization Specification in SQLAuthorization Specification in SQL
z The grant statement is used to confer authorization grant on to z is: a user-id public , which allows all valid users the privilege granted A role (more on this in Chapter 8) z Granting a privilege on a view does not imply granting any privileges on the underlying relations. z The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Privileges in SQLPrivileges in SQL
z select: allows read access to relation,or the ability to query using the view Example: grant users U 1 , U 2 , and U 3 select authorization on the branch relation: grant select on branch to U 1 , U 2 , U 3 z insert : the ability to insert tuples z update : the ability to update using the SQL update statement z delete : the ability to delete tuples. z all privileges : used as a short form for all the allowable privileges z more in Chapter 8
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Revoking Authorization in SQL Revoking Authorization in SQL
z The revoke statement is used to revoke authorization. revoke on from z Example: revoke select on branch from U 1 , U 2 , U 3 z <privilege-list> may be all to revoke all privileges the revokee may hold. z If <revokee-list> includes public, all users lose the privilege except those granted it explicitly. z If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation. z All privileges that depend on the privilege being revoked are also revoked.
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Embedded SQL (Cont.)Embedded SQL (Cont.)
z The open statement causes the query to be evaluated EXEC SQL open c END_EXEC z 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 END_EXEC Repeated calls to fetch get successive tuples in the query result z A variable called SQLSTATE in the SQL communication area (SQLCA) gets set to ‘02000’ to indicate no more data is available z The close statement causes the database system to delete the temporary relation that holds the result of the query. EXEC SQL close c END_EXEC Note: above details vary with language. For example, the Java embedding defines Java iterators to step through result tuples.
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Updates Through Cursors Updates Through Cursors
Can 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 update To update tuple at the current location of cursor c update account set balance = balance + 100 where current of c
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Dynamic SQLDynamic SQL
z Allows programs to construct and submit SQL queries at run time. z Example of the use of dynamic SQL from within a C program.
**char *** sqlprog = “ update account set balance = balance * 1. where account_number = ?” EXEC SQL prepare dynprog from :sqlprog; char account [10] = “A-101”; EXEC SQL execute dynprog using :account; z The dynamic SQL program contains a ?, which is a place holder for a value that is provided when the SQL program is executed.
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
ODBC and JDBC ODBC and JDBC
z API (application-program interface) for a program to interact with a database server z Application makes calls to Connect with the database server Send SQL commands to the database server Fetch tuples of result one-by-one into program variables z ODBC (Open Database Connectivity) works with C, C++, C#, and Visual Basic z JDBC (Java Database Connectivity) works with Java
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
ODBC Code ODBC Code
z int ODBCexample() { RETCODE error; HENV env; / environment / HDBC conn; / database connection / SQLAllocEnv(&env); SQLAllocConnect(env, &conn); SQLConnect(conn, "aura.bell-labs.com", SQL_NTS, "avi", SQL_NTS, "avipasswd", SQL_NTS); { …. Do actual work … }
SQLDisconnect(conn); SQLFreeConnect(conn); SQLFreeEnv(env); }
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
ODBC Code (Cont.)ODBC Code (Cont.)
z Program sends SQL commands to the database by using SQLExecDirect z Result tuples are fetched using SQLFetch() z SQLBindCol() binds C language variables to attributes of the query result When a tuple is fetched, its attribute values are automatically stored in corresponding C variables. Arguments to SQLBindCol() Ö ODBC stmt variable, attribute position in query result Ö The type conversion from SQL to C. Ö The address of the variable. Ö For variable-length types like character arrays, The maximum length of the variable Location to store actual length when a tuple is fetched. Note: A negative value returned for the length field indicates null value z Good programming requires checking results of every function call for errors; we have omitted most checks for brevity.
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
ODBC Code (Cont.)ODBC Code (Cont.)
z Main body of program char branchname[80]; float balance; int lenOut1, lenOut2; HSTMT stmt; SQLAllocStmt(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); while (SQLFetch(stmt) >= SQL_SUCCESS) { printf (" %s %g\n", branchname, balance); } } SQLFreeStmt(stmt, SQL_DROP);
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
More ODBC FeaturesMore ODBC Features
z Prepared Statement SQL statement prepared: compiled at the database Can have placeholders: E.g. insert into account values(?,?,?) Repeatedly executed with actual values for the placeholders z Metadata features finding all the relations in the database and finding the names and types of columns of a query result or a relation in the database. z By default, each SQL statement is treated as a separate transaction that is committed automatically. Can turn off automatic commit on a connection Ö SQLSetConnectOption(conn, SQL_AUTOCOMMIT, 0)} transactions must then be committed or rolled back explicitly by Ö SQLTransact(conn, SQL_COMMIT) or Ö SQLTransact(conn, SQL_ROLLBACK)
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
JDBC CodeJDBC Code
public static void JDBCexample(String dbid, String userid, String passwd) { try { Class.forName ("oracle.jdbc.driver.OracleDriver"); Connection conn = DriverManager.getConnection( "jdbc:oracle:thin:@aura.bell- labs.com:2000:bankdb", userid, passwd); Statement stmt = conn.createStatement(); … Do Actual Work …. stmt.close(); conn.close(); } catch (SQLException sqle) { System.out.println("SQLException : " + sqle); } }
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
JDBC Code (Cont.) JDBC Code (Cont.)
z Update to database try { stmt.executeUpdate( "insert into account values ('A-9732', 'Perryridge', 1200)"); } catch (SQLException sqle) { System.out.println("Could not insert tuple. " + sqle); } z 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()) { System.out.println( rset.getString("branch_name") + " " + rset.getFloat(2)); }
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
JDBC Code DetailsJDBC Code Details
z Getting result fields: rs.getString(“branchname”) and rs.getString(1) equivalent if branchname is the first argument of select result. z Dealing with Null values int a = rs.getInt(“a”); if (rs.wasNull()) Systems.out.println(“Got null value”);
Computing & Information Sciences CIS 560: Database System Concepts Friday, 08 Sep 2006 Kansas State University
Procedural Extensions and
Stored Procedures
Procedural Extensions and
Stored Procedures
z SQL provides a module language Permits definition of procedures in SQL, with if-then-else statements, for and while loops, etc. more in Chapter 9 z Stored Procedures Can store procedures in the database then execute them using the call statement permit external applications to operate on the database without knowing about internal details z These features are covered in Chapter 9 (Object Relational Databases)
