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Frequently asked SQL interview questions answer 1 - What is SQL and what are its main features? Answer: SQL (Structured Query Language) is a domain-specific language used for managing and manipulating relational databases. Main features of SQL include: -Data query and retrieval -Data insertion, update, and deletion -Schema creation and modification -Data access control -Transaction management 2 - Order of writing SQL query? Answer: The general order of writing an SQL query is: 1.SELECT 2.FROM 3.WHERE 4.GROUP BY 5.HAVING 6.ORDER BY 7.LIMIT/OFFSET (for databases that support pagination) 3 - Order of execution of SQL query? Answer: The order of execution of an SQL query is: 1.FROM clause 2.WHERE clause 3.GROUP BY clause 4.HAVING clause 5.SELECT clause 6.ORDER BY clause 4 - What are some of the most common SQL commands? Answer: Some of the most common SQL commands are: -SELECT: Retrieves data from a database -INSERT: Adds new data to a database -UPDATE: Modifies existing data in a database -DELETE: Removes data from a database -CREATE: Creates a new database, table, or view -ALTER: Modifies a database, table, or view structure -DROP: Deletes a database, table, or view -JOIN: Combines rows from two or more tables based on a related column 5 - What’s a primary key & foreign key? Answer: * Primary Key: A primary key is a unique identifier for a record in a table. It ensures that each record in a table is unique and not null. * Foreign Key: A foreign key is a column or a set of columns in a table that establishes a link between the data in two tables. It establishes a relationship between the two tables and ensures referential integrity. 6 - All types of joins and questions on their outputs? Answer: Types of joins in SQL include: -INNER JOIN: Returns records that have matching values in both tables. -LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table, and the matched records from the right table. If no match, NULL values are returned. -RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table, and the matched records from the left table. If no match, NULL values are returned. -FULL JOIN (or FULL OUTER JOIN): Returns all records when there is a match in either the left or right table. If no match, NULL values are returned. 7 - Explain all window functions and difference between them? Answer: Window functions perform calculations across a set of table rows that are related to the current row. Common window functions include: -ROW_NUMBER(): Assigns a unique sequential integer to rows within a partition of a result set. -RANK(): Assigns a unique rank to rows within a result set. -DENSE_RANK(): Similar to RANK() but without gaps in the ranking. -NTILE(n): Divides the result set into n equally sized groups. -LEAD(): Provides access to subsequent rows from the current row. -LAG(): Provides access to previous rows from the current row. 8 - What is stored procedure? Answer: A stored procedure is a precompiled collection of one or more SQL statements and control-of-flow statements stored under a name in a database. It can be invoked using a simple call, providing better performance and security, and promoting modular programming. 9 - Difference between stored procedure & Functions in SQL? Answer: *Stored Procedure: Can perform multiple SQL operations. Can have input and output parameters. Can't be used in SQL queries. Can't be used in SELECT statements. *Function: Returns a single value. Accepts only input parameters, doesn’t accept output parameters. Can be used in SQL queries. Can be used in SELECT statements.