Introduction To Oracle

A Relational Database Management System (RDBMS) can perform a wide range of tasks. It acts as a transparent interface between the physical storage and the logical presentation of data.It provides a set of more or less flexible and sofesticated tools for handling information. Users can use the tools to · Define a Database · Query the Database · Add,Edit and Delete data. · Modify the structure of the Database. · Communicate with in the Networks. · Exports and Imports the data. · Security. The Oracle Environment Oracle is a modular system that consists of the Oracle database and several functional programs. Oracle's tools do four major things of work. 1. Database Management. 2. Data access and Manipulation. 3. Programming 4. Connectivity. Database Management Tools This (is usually known as RDBMS by oracle) includes the core programs for Oracle's database management system, the Oracle database with its associated tables and views, which are stores information related to every fact of the database system.User name, user access rights, table attribute, storage information and auditing data for disaster recovery are stored in the data dictionary. The Database Administrator The person responsible for a Database is called the DatabaseAdministrator(DBA).The DBA has a special set of previleges and has complete over the database.Any system with more than one user should have a DBA.The function of DBA include. Creating primary database storage structures. Modifying the structure of the database. Backing up and restoring the database. Monitoring database performance and efficiency. Transfering data between database and external files. Manipulating the phisical location of the database. THE END USER End user have less complex but equally important tasks.They must be able to · Query the database. · Generate printed output. · Share data with or secure data from others. · Use non-export methods to update the database. · Define applications from a user point of view. WHY ORACLE ? Oracle is an open system i.e. the database is accessing by different data access languages like SQL, Visual Basic, Power Builders,Delphi,VC++,JAVA etc.

Oracle supports database upto gigabytes in size. * Oracle supports large number of concurrent users. * Oracle supports true client/server environment.if enable processing to be spilt between database server and the client application programs. * Oracle provides high levelof data security in terms of users, passwords privileges, and permissions. * Oracle database behaves same on all platform line Windows,Unix,Dos,Mainframes etc. STRUCTURE OF ORACLE physical structure: one or more data files, Two of more log files, One control file. Logical structure: Table spaces, Segments, Extents, Data blocks. The data files contain all user data in terms of tables, index, and views. The log files contain the information to open and be recovered, of Undone after a transaction(Rollback). The control file physical data, media information to open and manage data files .If the control file is damaged the server will not be able to open are use the database even if the database is undamaged. What are the Back ground processes in Oracle and what are they. ? There are basically 9 Processes but in a general system we need to mention the first five background processes. They do the house keeping activities for the Oracle and are common in any system. a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is required since the data is not written whenever a transaction is commited. b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log buffer of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online redo log file. c) System Monitor(SMON) :: The System Monitor performs instance recovery at instance startup. This is useful for recovery from system failure. d)Process Monitor(PMON) :: The Process Monitor peforms process recovery when user Process fails. Pmon Clears and Frees resources that process was using. e) CheckPoint(CKPT) :: At Specified times, all modified database buffers in SGA are written to data files by DBWR at Checkpoints and Updating all data files and control files of database to indicate the most recent checkpoint. f)Archieves(ARCH) :: The Archiver copies online redo log files to archival storal when they are busy. g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed transaction in network h) Dispatcher (Dnnn) :: The Dispatcher is useful in

Multi Threaded Architecture i) Lckn :: We can have upto 10 lock processes for inter instance locking in parallel sql. NORMALIZATION Normalization is a process of simplifying the relationship between data elements in a record. Through Normalization a collection of data in a record structure is replaced by successive record structures that are simpler and more predictable and therefore more manageable. It is process of reducing redundancy and eliminating the anomalies. (anamali means inconsistent state.) Normalization is carried out for four reasons: · To Structure the data so that any pertinent relationships between entities can be represented. · To permit simple retrieval of data in response to query and report requests. · To simplify the maintenance of the data through updates, insertions, and deletion · To reduce the need to restructure or reorganize data when new application requirements arise. · Normalization can improve the quality of design for an application. There are totally Five Normal Forms(Rules) out of which, any database should necessarily satisfy three of them, those Three Normal Forms are as follows: First normal form is achieved when all repeating groups are removed so that a record is of fixed length. A repeating group, the re-occurrence of a data item within a record, is actually another relation. Hence, it is removed from the record and treated as an additional record structure, or relation. Second Normal form should be in first normal form and no partial dependency exists. Means if we have a composite primary key(combination of 2 or more fields) then all the non keys must depend on the composite primary key. no attribute should depend upon the part of key.(for example if Rollno and SSno is a composite key, then no other field in that particular table should be depedent upon either Rollno or ssno individually) Third Normal form is achieved when Transitive Dependencies are removed from a record design. The general case is as follows : A,B and C are three data items in a record. If C is functionally dependent on B (2nd N.F) and B is functionally dependent on A Then C is functionally dependent on A Therefore, a Transitive Dependency exists. In data management, transitive dependency is a concern because data can inadvertently be lost when the relationship is hidden. In the general case above, if A is deleted, then B and C are deleted also, whether or not this is intended. This problem is eliminated by designing the record

for third normal form. Conversion to third normal form removes the transitive dependency by splitting the relation into two separate relations. BCNF must be 3NF and every determinant is a candidate key. Candidate key is other than primary key, which uniquely identify each row in the table. for example ssno is PK then rollno becomes Candidate key. 4NF and 5NF are depends on instance. we can not give a proper def. bcz it all depends on joins. "CODD's 12 RULES" for a fully Relational DBMS INTRODUCTION According to Elmasri and Navathe (1994), Dr. E. F. Codd, the originator of the relational data model, published a two-part article in ComputerWorld (Codd, 1985) that lists 12 rules for how to determine whether a DBMS is relational and to what extent it is relational. These rules provide a very useful yardstick for evaluating a relational system. Codd also mentions that, THE 12 RULES Rule 1: The Information Rule All information in a relational database is represented explicitly at the logical level in exactly one way by values in tables. All data is represented in the form of relations/tables (with rows and columns)Simple Consistent and versatile Rule 2: Guaranteed Access Rule Each and every datum (atomic value) in a relational database is guaranteed to be logically accessible by resorting to a table name, primary key value, and column name. All Data is uniquely identified and accessible via this identity. Rule 3: Systematic Treatment of Null Values Null values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type. Rule 4: Dynamic On-line Catalog based on the Relational Model The database description is represented at the logical level in the same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to regular data. Rule 5: Comprehensive Data Sublanguage Rule A relational system may support several languages and various modes of terminal use (for example, the fill-in-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and whose ability to support all of the following is comprehensible: data definition, view definition, data manipulation (interactive and by program), integrity constraints, and transaction boundaries (begin, commit, and rollback). Rule 6: View Updating Rule All views that are theoretically updateable are also updateable by the system. Views are virtual tables. They appear to behave as

conventional tables except that they are built dynamically when the query is run. This means that a view is always up to date. It is not always theoretically possible to update views. One problem exists when a view relates to part of a table not including a candidate key. This means that potential updates would violate the entity integrity rule. Rule 7: High-level Insert, Update, and Delete The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update, and deletion of data. i.e. The user should be allowed to Delete, Update a set of tuples (rather than row by row) Rule 8: Physical Data Independence Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods. i.e. Users and programs are not dependent on the physical structure of the database. Rule 9: Logical Data Independence Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit unimpairment are made to the base tables. Users and Programs are independent of the logical structure of the database, i.e. the logical structure of the data can evolve with minimal impact on the programs. Rule 10: Integrity Independence Integrity constraints specific to a particular relational database must be definable in the relational data sublanguage and storable in the catalog, not in the application programs. A minimum of the following two integrity constraints must be supported: 1. Entity integrity: No component of a primary key is allowed to have a null value. 2. Referential integrity: For each distinct non-null foreign key value in a relational database, there must exist a matching primary key value from the same domain. Rule 11: Distribution Independence A relational DBMS has distribution independence. Distribution independence implies that users should not have to be aware of whether a database is distributed. Applications should still work in a distributed database (DDB). Rule 12: Nonsubversion Rule If a relational system has a low-level (single-record-ata-time) language, that low-level language cannot be used to subvert or bypass the integrity rules or constraints expressed in the higher-level (multiple-records-at-a-time) relational language. If there is a record at a time interface (e.g. via 3GL), Security and integrity of the database must no be violated. There should be no backdoor to bypass the security imposed by the DBMS. On the basis of the above rules, there is no fully relational DBMS available today. Questions and Answers : What is Pseudo Colomn ? USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL How to Display output in PL/SQL ?

we first set serveroutput on at SQL Prompt. and then in sql programming we specify as dbms_output.put_line(`hdjhd' || `sakdha'); No Displays are allowed in PL/SQL programming with select statement Write about Commands and Keywords ? Alter : ALTER TABLE EMP ADD .......... , MODIFY .......... ; for a in 1..10 loop ........... end loop; loop exit when a<1 .................. end loop; while ..... loop.................end loop; Data Types : number, integer, varchar2, char, date, Boolean; goto procedure name;..............<<procedure name>>.............. exit, rollback, commit, savepoint. References: This keyword is used to refer two similar fields of different tables. What are different built in functions ? CONCATENATE, INITCAP, LENGTH, LOWER, UPPER, LPAD, RPAD, LTRIM (removes the character specified left side of word), RTRIM, SUBSTR (displays values from specified location onwards), TRANSLATE (for single character), REPLACE (for more than one character ),CHR ( prints character of given ASCII value), ASCII (value of given character ). ABS, CEIL, FLOOR, SQRT, POWER, SIGN, TRUNC, ROUND, EXP, MOD, LOG, LN, GREATEST, LEAST, SYSDATE, ADD_MONTHS, MONTHS_BETWEEN. what are emp.sal%type and emp%rowtype ? First one is to assign a variable of type sal only. Second is to assign a complete row of type emp table. What are constraints ? Constraint Clause : This will constrain a single column or a group of columns in a table. and are used for maintaining integrity of the database. Different Constraints are : candidate keys, primary keys, foreign keys, check conditions. Can specify as a part of column definition, or at the end of the table (if more than one column). Check Constraint : for validations to fields. Naming Constraint (table constraints): Can name the constraint else system will name it by default.

Different types of joins ? Equi join : where emp.deptno = dept.deptno; Non Equi join : where e.sal >= g.losal; Outer join :***********e.deptno(+)=d.deptno; Different types of Keys ? Foreign Key : This is a referential integrity constraint and specifies the values of primary key in other table. and is mentioned as : DEPTNO number(2) REFERENCES DEPT(DEPTNO); The clause ON DELETE CASCADE added to REFERENCES clause tells Oracle to delete the dependent rows when we delete the row in the parent table. Unique Key : If declared, then does not accept duplicate and also NULL values. And can have many

Unique key fields. Primary Key : Similar to Unique key but, also maintains an index on primary key and also used to connect two tables. Write about cursors ? Implicit (SQL is implicit by default ) and Explicit cursors. EXIT WHEN C1%NOTFOUND, IF C1%FOUND THEN, IF C1%ISOPEN THEN, FOR LOOP in CURSOR will : 1) open the cursor. 2) fetches the records from cursor one by one. 3) keeps the track of number of records in the cursor. Super Dynamism in Cursors is obtained by passing the values as parameters( ie pass by value) ie., for x in c1(a,b) Multiple Cursors : These are nothing but nested cursors........... In Implicit Cursors there is no need of declaration of cursors, by default system will create a cursor whenever a query is written...and the conditions are like if SQL%NOTFOUND if SQL%ROWCOUNT > 2 will keep a count of the number of records updated. SQL is a keyword and cannot be used to name as a cursor name explicitly. Difference between group functions and single row functions ? Group Function Single Row Function A group function operates A single row function on many rows returns one and result for one row. returns single result. Not allowed in Pl/sql procedural Allowed in Pl/Sql Procedural statements eg SUM(),AVG,MIN,MAX etc eg UPPER,LOWER,CHR... Difference between DECODE and TRANSLATE ? DECODE is value by value TRANSLATE is character by character replacement. replacement. Ex SELECT DECODE('ABC','A',1,'B',2,'ABC',3) eg SELECT from dual; o/p 3 TRANSLATE('ABCGH', 'ABCDEFGHIJ', 1234567899) FROM DUAL; o/p 12378 (DECODE command is used to bring IF,THEN,ELSE logic to SQL.It tests for the IF values(s) and then aplies THEN value(s) when true, the ELSE value(s) if not.) Difference between TRUNCATE and DELETE ? TRUNCATE deletes much faster than DELETE Truncate Delete It is a DDL statement It is a DML statement It is a one way trip,cannot One can Rollback ROLLBACK Doesn't have selective features (where clause) Has Doesn't fire database triggers Does It requires disabling of referential Does not require constraints.

What is a CO-RELATED SUBQUERY ? A CO-RELATED SUBQUERY is one that has a correlation name as table or view designator in the FROM clause of the outer query and the same correlation name as a qualifier of a search condition in the WHERE clause of the subquery. eg SELECT field1 from table1 X WHERE field2>(select avg(field2) from table1 Y where field1=X.field1); (The subquery in a correlated subquery is revaluated for every row of the table or view named in the outer query.) What are various joins used while writing SUBQUERIES ? Self join-Its a join foreign key of a table references the same table.

Outer Join--Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don't satisfy the join condition. Equi-join--Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table. What are various constraints used in SQL ? NULL, NOT NULL, CHECK, DEFAULT What are different Oracle database objects ? TABLES, VIEWS, INDEXES, SYNONYMS, SEQUENCES, TABLESPACES etc What is difference between Rename and Alias ? Rename is a permanent name given to a table or column whereas Alias is a temporary name given to a table or column which do not exist once the SQL statement is executed. What is a view ? A view is stored procedure based on one or more tables, it's a virtual table. What are various privileges that a user can grant to another user ? SELECT, CONNECT, RESOURCES What is difference between UNIQUE and PRIMARY KEY constraints ? A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys. The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL. Can a primary key contain more than one columns ? Yes How you will avoid duplicating records in a query ? By using DISTINCT What is difference between SQL and SQL*PLUS ? SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and reporting tool. Its a command line tool that allows user to type SQL commands to be executed directly against an Oracle database. SQL is a language used to query the relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options, Edit SQL commands and PL/SQL. Which datatype is used for storing graphics and images ? LONG RAW data type is used for storing BLOB's (binary large objects).

How will you delete duplicating rows from a base table ? DELETE FROM table_name A WHERE rowid>(SELECT min(rowid) from table_name B where B.table_no=A.table_no); CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table; DROP old_table RENAME new_table TO old_table DELETE FROM table_name A WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name GROUP BY column_name)