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By: TrendnologiesAdmin
- October 8, 2024
Oracle SQL Interview Questions and Answers
Top 20 Oracle SQL Interview Questions and Answers Oracle SQL is a powerful, high-performance database language used for managing and manipulating relational databases. It is the industry standard for interacting with Oracle databases and is based on the SQL (Structured Query Language) standard with some Oracle-specific extensions. Oracle SQL allows users to create, modify, and manage database objects like tables, views, indexes, and more. It supports CRUD operations (Create, Read, Update, Delete), complex queries, joins, subqueries, aggregation, and functions, enabling efficient data manipulation and retrieval. 1. What is Oracle SQL? Oracle SQL is the structured query language used to communicate with Oracle databases, enabling data retrieval, manipulation, and management. 2. What is a table in Oracle? A table is a database object that stores data in rows and columns. Each row represents a record, and each column represents a field. 3. What is a primary key in Oracle SQL? A primary key is a column or set of columns that uniquely identifies each row in a table. It enforces uniqueness and does not allow null values. 4. What is a foreign key? A foreign key is a column or set of columns in one table that refers to the primary key in another table, creating a relationship between the two tables. 5. What are constraints in Oracle SQL? Constraints are rules applied to table columns to enforce data integrity. Common constraints include PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, and CHECK. 6. What is a view? A view is a virtual table based on the result of an SQL query. It does not store data physically but provides a way to look at data from one or more tables. 7. What is a join in SQL? A join is a query that combines rows from two or more tables based on a related column. Common types include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN. 8. What are aggregate functions in Oracle SQL? Aggregate functions perform calculations on multiple rows and return a single result. Common aggregate functions include SUM(), AVG(), COUNT(), MAX(), and MIN(). 9. What is a GROUP BY clause? The GROUP BY clause is used to group rows with the same values in specified columns and apply aggregate functions to each group. 10. What is a sequence in Oracle? A sequence is a database object that generates a series of unique numbers, typically used for primary keys. 11. What are indexes in Oracle SQL? Indexes are database objects that improve query performance by allowing faster retrieval of rows. Common index types include B-tree, Bitmap, and Unique. 12. What is a cursor in Oracle? A cursor is a pointer to a result set of a query. It is used to process rows returned by the query one at a time. 13. What is the difference between an implicit and explicit cursor? An implicit cursor is automatically created by Oracle when a query is executed, whereas an explicit cursor must be declared and opened by the user to retrieve multiple rows. 14. What are synonyms in Oracle SQL? Synonyms are aliases for database objects such as tables, views, sequences, or functions, used to simplify access. 15. What is normalization? Normalization is the process of organizing a database into tables and columns to reduce data redundancy and improve data integrity. 16. What is denormalization? Denormalization is the process of combining tables to reduce the complexity of queries and improve performance by adding redundancy. 17. What is a PL/SQL block? A PL/SQL block is a logical unit of code that contains procedural language constructs like variables, conditions, loops, and SQL statements. It has three parts: Declaration, Execution, and Exception handling. 18. What is the ROWNUM in Oracle SQL? ROWNUM is a pseudo-column that assigns a unique number to each row returned by a query. 19. What is the difference between DELETE and TRUNCATE? DELETE removes rows from a table and can be rolled back, while TRUNCATE removes all rows from a table but cannot be rolled back. 20.What is a partition in Oracle SQL? Partitioning is a database feature that divides large tables into smaller, more manageable pieces, improving performance and scalability. 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