Certainly! Here are 20 SQL questions and answers:
Q: What is SQL?
A: SQL (Structured Query Language) is a programming language used for managing and manipulating relational databases.
Q: What are the main components of an SQL statement?
A: An SQL statement consists of keywords, expressions, and clauses such as SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY.
Q: What is a database in SQL?
A: A database in SQL is a collection of organized data that is stored and accessed using a database management system (DBMS).
Q: What is a table in SQL?
A: A table in SQL is a structured data object that stores related data in rows and columns.
Q: How do you create a table in SQL?
A: You can create a table in SQL using the CREATE TABLE statement, specifying the table name and column definitions.
Q: What is a primary key in SQL?
A: A primary key in SQL is a column or a combination of columns that uniquely identifies each row in a table.
Q: What is a foreign key in SQL?
A: A foreign key in SQL is a column that establishes a link or relationship between two tables based on the values in the respective columns.
Q: What is a JOIN in SQL?
A: JOIN is an SQL operation used to combine records from two or more tables based on a related column between them.
Q: What is the difference between INNER JOIN and OUTER JOIN?
A: INNER JOIN returns only the matching records between two tables, while OUTER JOIN returns all records from both tables, including unmatched records.
Q: What is a WHERE clause in SQL?
A: A WHERE clause in SQL is used to filter records based on a specified condition or criteria.
Q: What is the purpose of the GROUP BY clause in SQL?
A: The GROUP BY clause in SQL is used to group rows based on one or more columns and apply aggregate functions to each group.
Q: What are aggregate functions in SQL?
A: Aggregate functions in SQL are functions that perform calculations on a set of values and return a single value, such as SUM, AVG, COUNT, MIN, and MAX.
Q: What is a subquery in SQL?
A: A subquery in SQL is a query nested within another query, used to retrieve data that depends on the result of the outer query.
Q: What is the purpose of the ORDER BY clause in SQL?
A: The ORDER BY clause in SQL is used to sort the result set in ascending or descending order based on one or more columns.
Q: What is a view in SQL?
A: A view in SQL is a virtual table derived from one or more tables, which can be queried like a regular table.
Q: What is normalization in SQL?
A: Normalization is the process of organizing data in a database to eliminate redundancy and improve data integrity.
Q: What is a stored procedure in SQL?
A: A stored procedure in SQL is a set of pre-compiled SQL statements that are stored in the database and can be executed repeatedly.
Q: What is ACID in the context of database transactions?
A: ACID stands for Atomicity, Consistency, Isolation, and Durability, which are properties that ensure the reliability and integrity of database transactions.
Q: What is a trigger in SQL?
A: A trigger in SQL is a set of SQL statements that are automatically executed or fired in response to specified database events, such as INSERT, UPDATE, or DELETE operations.
Q: What is the purpose of the UNION operator in SQL?
A: The UNION operator in SQL is used to combine the result sets of two or more SELECT statements into a single result set, removing duplicate rows.