SQL Query вопросы и ответы для интервью

Вопрос 16. Explain the GROUP BY clause.

The GROUP BY clause is used in a SELECT statement to arrange identical data into groups, typically used with aggregate functions.

Example:

SELECT column, COUNT(*) FROM table GROUP BY column;

Вопрос 17. What is a stored procedure?

A stored procedure is a set of SQL statements that can be stored in the database and executed by calling the procedure.

Вопрос 18. Write a SQL query to find duplicate records in a table.

SELECT column, COUNT(*) FROM table GROUP BY column HAVING COUNT(*) > 1;

Вопрос 19. Explain the purpose of the HAVING clause.

The HAVING clause is used in combination with the GROUP BY clause to filter the results of aggregate functions based on specified conditions.

Example:

SELECT column, COUNT(*) FROM table GROUP BY column HAVING COUNT(*) > 1;

Вопрос 20. What is a view in a database?

A view is a virtual table based on the result of a SELECT query, and it does not store the data itself.

Example:

CREATE VIEW view_name AS SELECT column1, column2 FROM table WHERE condition;