Oracle DBA Interview Questions

List top 15+ most asked Oracle database interview question and answers for freshers and experienced candidates.

Oracle is a secured database. Try to cover almost all the basic concepts based questions of Oracle.

Oracle database interview question
Oracle database Interview Questions

Q1- What is an Oracle table?

A table used to contains all the accessible information of a user in rows and columns.

Q2- What is joins in Oracle?

Joins are used to extract data from multiple tables using some common column or condition.

Q3- What are UNION and UNION All Operators in Oracle?

UNION operator used to returns all the rows from both the tables except the duplicate rows.
UNION ALL operator used to returns all the rows from both the tables along with the duplicate rows.

Q4- What are the types of joins?

There are six joins used in Oracle datamabase, mentained below:

  • Inner Join
  • Outer Join
  • Cross Join
  • Anti Join
  • Semi Join
  • Equi Join

Q5- Which language has been used to developed Oracle?

Oracle has been developed using C Language.

Q6- What aree nested tables?

Nested table hold entire sub table. It is a data type in Oracle which is used to support columns containing multi-valued attributes.

Q7- What are the various Oracle database objects

  • Table - Set of elements organized in vertical and horizontal
  • Tablespaces - Logical storage unit in Oracle.
  • Views - Virtual table derived from one or more tables.
  • Indexes - Performance tuning method to process the records.
  • Synonyms - Name for tables.

Q8- What is a tablespace?

A tablespace is a set of related logical structures. It contains a logical storage unit.

Q9- What is a Primary Key?

In Oracle, Primary key is used to identify each table row uniquely, and Primary key never hold null value. Only one primary key usee in a table.

Q10- What is the query to find out the current date & time in Oracle?

We can find the current Date & Time using SYSDATE in Oracle.
Syntax -

Q11- What is COALESCE function?

COALESCE function is used to return the value which is set to be not null in the list. Supposed If all values in the list are null, then the coalesce function will return NULL.

Q12- What is the list of Aggregate functions in Oracle?

Basically, Aggregate functions in Oracle perform summary operations on a set of values to provide a single value.

  • AVG
  • MIN
  • MAX
  • SUM

Q13- How many memory layers are in the Oracle shared pool?

There are two memory layers in Oracle shared pool:

  • library cache
  • data dictionary cache

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