Dear Readers, Welcome to Oracle Developer Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Oracle Developer. These Oracle Developer Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT companies.
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.
A database link is a named object that describes a path from one database to another.
Private Database Link, Public Database Link & Network Database Link.
Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner's views or procedures.
Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.
Network database link is created and managed by a network domain service. A
network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.
ORACLE databases data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
A data block size is specified for each ORACLE database when the database is
created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and cannt be changed latter.
ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files.
Tablespaces and the Databases Schema Objects.
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.
Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.
Each databases logically divided into one or more tablespaces One or more data files are explicitly created for each tablespace.
A schema is collection of database objects of a User.
Schema objects are the logical structures that directly refer to the database's data.
Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)
Views do not contain or store data.
Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table. Hide data complexity. Simplify commands for the user. Present the data in a different perpecetive from that of the base table. Store complex queries.
A sequence generates a serial list of unique numbers for numerical columns of a databases tables.
A synonym is an alias for a table, view, sequence or program unit.
There are two types of Synonyms Private and Public.
A Private Synonyms can be accessed only by the owner.
A Public synonyms can be accessed by any user on the database.
Synonyms are used to :
Mask the real name and owner of an object. Provide public access to an object Provide location transparency for tables,views or program units of a remote database. Simplify the SQL statements for database users.
An Index is an optional structure associated with a table to have direct access to rows,which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
The related columns of the tables in a cluster is called the Cluster Key.
A Cluster with an index on the Cluster Key.
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.
The condition must be a Boolean expression evaluated using the values in the row being inserted or updated and can't contain subqueries, sequence, the SYSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.
If a foreign key reference a parent key of the same table is called self-referential integrity constraint.
In Circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs , the data for the row is stored in a chain of data block (one or more) reserved for that segment.
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, used to store a specific type of information.
A segment is a set of extents allocated for a certain logical structure.
Data Segment, Index Segment, Rollback Segment and Temporary Segment.
Each Non-clustered table has a data segment. All of the tables data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is
Each Index has an Index segment that stores all of its data.
A Database contains one or more Rollback Segments to temporarily store "undo" information.
Rollback Segments are used : To generate read-consistent database information during database recovery to rollback uncommitted transactions for users.
Temporary segments are created by ORACLE when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.
Every ORACLE database has one or more physical data files. A databases data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.
A data file can be associated with only one database.Once created a data file cant change size.
The set of Redo Log files for a database is collectively known as the databases redo log.
The Primary function of the redo log is to record all changes made to data.
The Information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a databases data files.
A Control file records the physical structure of the database. It contains the following information.
Database Name, Names and locations of a databases files and redolog files. ,Time stamp of database creation.
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
The data dictionary of an ORACLE database is a set of tables and views that are used as a read-only reference about the database. It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used.
An integrity constraint is a declarative way to define a business rule for a column of a table.
SGA and ORACLE background processes constitute an ORACLE instance. (or) Combination of memory structure and background process.
The System Global Area (SGA) is a shared memory region allocated by ORACLE that contains data and control information for one ORACLE instance.
Database buffers, Redo Log Buffer the Shared Pool and Cursors.
Database buffers store the most recently used blocks of database data. It can also contain modified data that has not yet been permanently written to disk.