55+ TOP Oracle Developer Questions and Answers
1. When can Hash Cluster used?
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.
2. Explain Database Link?
A database link is a named object that describes a path from one database to another.
3. What are the types of Database Links?
Private Database Link, Public Database Link & Network Database Link.
4. What is Private 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.
5. What is Public Database Link?
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.
6. What is Network Database link?
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.
7. What is Data Block?
ORACLE databases data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
8. How to define Data Block size?
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 data blocks. Block size is specified in INIT.ORA file and cann’t be changed latter.
9. What are the components of Physical database structure of Oracle Database?
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.
10. What are the components of Logical database structure of ORACLE database?
Tablespaces and the Databases Schema Objects.
11. What is Tablespace?
A database is divided into Logical Storage Unit called table spaces. A table space is used to grouped related logical structures together.
12. What is SYSTEM tablespace and When is it Created?
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.
13. Explain the relationship among Database, Tablespace and Data file?
Each databases logically divided into one or more tablespaces One or more data files are explicitly created for each tablespace.
14. What is schema?
A schema is collection of database objects of a User.
15. What are Schema Objects?
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.
16. Can a Tablespace hold objects from different Schemes?
17. Explain Table?
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.
18. Explain View?
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.)
19. Explain Can a View based on another View?
20. Explain Do View contain Data?
Views do not contain or store data.
21. Explain What are the advantages of Views?
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.
22. What is Sequence?
A sequence generates a serial list of unique numbers for numerical columns of a databases tables.
23. Explain a Synonym?
A synonym is an alias for a table, view, sequence or program unit.
24. Explain What are the type of Synonyms?
There are two types of Synonyms Private and Public.
25. Explain a Private Synonyms?
A Private Synonyms can be accessed only by the owner.
26. What is a Public Synonyms?
A Public synonyms can be accessed by any user on the database.
27. Explain What are synonyms used for?
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.
28. Explain an Index?
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.
29. Explain How are Indexes Update?
Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.
30. Explain What are Clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
31. What is cluster Key?
The related columns of the tables in a cluster is called the Cluster Key.
32. What is Index Cluster?
A Cluster with an index on the Cluster Key.
33. What is Hash Cluster?
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.
34. What is the maximum number of CHECK constraints that can be defined on a column?
35. What are the Limitations of a CHECK Constraint?
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.
36. What is self-referential integrity constraint?
If a foreign key reference a parent key of the same table is called self-referential integrity constraint.
37. What is Row Chaining?
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.
38. Explain an Extent?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, used to store a specific type of information.
39. Explain a Segment?
A segment is a set of extents allocated for a certain logical structure.
40. Explain What are the different type of Segments?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.
41. Explain a Data 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
42. Explain an Index Segment?
Each Index has an Index segment that stores all of its data.
43. What is Rollback Segment?
A Database contains one or more Rollback Segments to temporarily store “undo” information.
44. Explain What are the uses of Rollback Segment?
Rollback Segments are used : To generate read-consistent database information during database recovery to rollback uncommitted transactions for users.
45. What is a Temporary Segment?
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.
46. What is Data File?
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.
47. Explain What are the Characteristics of Data Files?
A data file can be associated with only one database.Once created a data file cant change size.
48. What is Redo Log?
The set of Redo Log files for a database is collectively known as the databases redo log.
49. What is the function of Redo Log?
The Primary function of the redo log is to record all changes made to data.
50. What is the use of Redo Log Information?
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.
51. Explain What does a Control file Contain?
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.
52. Explain the use of Control File?
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.
53. What is a Data Dictionary?
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.
54. Explain an Integrity Constrains?
An integrity constraint is a declarative way to define a business rule for a column of a table.
55. What constitute an ORACLE Instance?
SGA and ORACLE background processes constitute an ORACLE instance. (or) Combination of memory structure and background process.
56. What is SGA?
The System Global Area (SGA) is a shared memory region allocated by ORACLE that contains data and control information for one ORACLE instance.
57. What are the components of SGA?
Database buffers, Redo Log Buffer the Shared Pool and Cursors.
58. What do Database Buffers contain?
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.