What is SQL? Ans- SQL stands for structure Query language . It is used to communicate with and manage relational database. What are the different types of SQL commands? Ans- SQL commands are classified into five categories. *DDL *DML *DCL *TCL *DQL What is a primary key in SQL? .. Ans- A primary key is a unique identifier for a record in a table. It ensures that each record in a table is unique. What is a foreign key? Ans-A foreign key is a column in one table that refers to the primary key in another table. Explain the difference between DELETE and TRUNCATE commands. Ans-TRUNCATE removes all rows from a table and cannot be rolled back, while DELETE removes rows one at a time and can be rolled back if in a transaction. What is a JOIN in SQL, and what are its types? Ans-In SQL, a JOIN is used to combine records from two or more tables based on a related column between them. INNER JOIN,LEFT JOIN,RIGHT JOIN,RIGHT JOIN,CROSS JOIN,SELF JOIN What do you mean by a NULL value in SQL? Ans-In SQL, a NULL value represents missing or unknown data. It is not the same as an empty string (''), zero (0), or any other default value. Rather, NULL indicates that the value is either: Not assigned yet Unknown Inapplicable