Oracle Interview Questions and answers

The answer here is not comprehensive. These questions can be explained from multiple perspectives. Maybe you don't have to give a full answer during the interview, you only need to answer your questions to familiarize the interview examiner with Oracle concepts.

1. Explain the differences between cold backup and hot backup and their respective advantages

Answer: Hot Backup is applicable to databases in the archive mode. When the database is still in the working state, it is backed up. Cold backup refers to the backup after the database is closed, applicable to all databases. The advantage of hot backup is that the database can still be used during Backup and can be restored to any point in time. The advantage of cold backup is that its backup and recovery operations are quite simple, and because cold backup databases can work in non-archive mode, the database performance will be slightly better than the archive mode. (Because archive log is not necessarily written to the hard disk)

2. You must use backup to restore the database, but you do not have control files. How can this problem be solved?

A: recreate the control file and use the recover command with the backup control file clause to restore the database.

3. How to convert init. ora to spfile?

A: Use the create spfile from pfile command.

4. Explain the differences between data block, extent, and segment (the term here is recommended)

A: data block is the smallest logical storage unit in the database. When database objects require more physical storage space, continuous data blocks constitute extent. All extents owned by a database object are called the segment of this object.

5. Two Methods of checking table structure are provided.

Answer: 1. Describe command

2. dbms_metadata.get_ddl package

6. How to view database engine errors

Answer: Alert Log.

7. Compare the truncate and delete commands

A: both of them can be used to delete all records in the table. The difference is that truncate is a DDL operation, which moves hwk and does not require rollback segment. Delete is a DML operation, which requires rollback segment and takes a long time.

8. Reasons for using Indexes

A: quick access to the data block in a table

9. Two types of tables in star schema and their data are given respectively.

Answer: fact tables and dimension tables. fact table contain a large amount of major information, while dimension tables stores information about certain attribute descriptions of fact table.

10. What indexes should be created on the fact table?

A: bitmap Index)

11. are two related constraints provided?

Answer: primary key and foreign key

12. How to recreate a parent table without affecting the sub-table?

A: The foreign key of the sub-table is forced to take effect. The parent table is rebuilt and the foreign key is activated.

13. Explain the differences between archive and non-archive modes and their respective advantages and disadvantages

A: In archive mode, you can back up all database transactions and restore them to any point in time. Non-archive mode, on the contrary, cannot be recovered to any point in time. However, the non-archive mode can slightly improve the database performance.

14. How to Create a backup control file?

Answer: Alter database backup control file to trace.

15. How many statuses does the database normally start?

Answer: startup nomount database instance startup

Startup Mount Database loading

Startup Open Database open

16. Which column can be used to distinguish between the V $ view and the GV $ view?

A: inst_id indicates a specific instance in the cluster environment.

17. How to generate an explain Plan?

A: Run utlxplan. SQL. Create a plan table.

For specific SQL statements, use the explain Plan set statement_id = 'tst1' into plan_table

Run utlxplp. SQL or utlxpls. SQL to check the explain Plan

18. How to Increase the buffer cache hit rate?

A: When the database is busy, use the buffer cache advisory tool to query v $ db_cache_advice. If necessary, use the alter system set db_cache_size command.

19. How should ORA-01555 respond?

A: The specific error message is snapshot too old within rollback Seg. Generally, you can increase the rollback seg to solve the problem. Of course, you also need to check the specific SQL text that causes the error.

20. What is the difference between $ ORACLE_HOME and $ oracle_base?

A: oracle_base is the root directory of Oracle and ORACLE_HOME is the directory of Oracle products.