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Oracle SQL Interview Questions and Answers Q1.) What does NVL function does? Ans: NVL function is mainly used to replace NULL values with some other value provided the data type of the NULL value to be replaced with the given value is same. Q3.) What is a BLOB data type? Ans: BLOB is a binary string of varying length used to store data up to 2 gigabytes. Images, videos and other documents can be stored in the database using BLOB data type. Q4.) What is the difference between var-char and varchar2? Ans: The data type var-char is used to stored data up to 2000 bytes while varchar2 is used to store data up to 4000 bytes. However, the prominent difference between var char and varchar2 is that var-char can occupy NULL values while varchar2 cannot.
SQL Queries Interview Questions and Answers Most common examples are: SELECT: Used to retrieve data from the database INSERT: Used to insert new data/records into the database UPDATE:Used to update/modify the existing data/record from the database DELETE: Used to remove the existing data/record from the database
Q5.) What are the different Oracle SQL database objects? Ans: Tables - Database object used to store various database records Views - It is a virtual table derived from one or more tables Indexes - Used to improve efficiency and performance of the database Synonyms - Aliases used for database tables Q6.) What are various types of integrity constraints in Oracle SQL? Ans: Unique: It ensures that the given column or entity is unique and cannot be duplicated. Not NULL: It ensures that the given column cannot be empty. Foreign: It ensures that the two entities/tables share a common key with the one in parent table being a primary key and the one in child table being a foreign key. Q7.) What is a hash cluster? Ans: It is used to store table in a manner that query fetching results in faster data retrieval by using the hashing technique.
Q8.) What is a sub query? Ans: Sub query refers to a query written with in a query. It is often referred to as nested query or inner query. It is used to apply filters on selected data retrieved by the main query. Q9.) What is an alert? Ans: A window appearing in the center of the screen overlaying the current screen to provide some form of information is termed as an alert. Q10.) Which is the fastest query method used to fetch data? Ans: Since Oracle uses clustering index technique, fetching records using ROWID is the fastest and the most efficient query method. If you looking for Oracle SQL Training in Bangalore, Sgraph Infotech is the best and top training center in Marathahalli in Bangalore.