DA SQL and Database Querying 2

Question 1

Which SQL function returns the current date and time?

Accepted Answer

NOW()

Answer

NOW() returns the current date and time in most SQL dialects, including MySQL and PostgreSQL.

Question 2

What is a subquery in SQL?

Accepted Answer

A query nested inside another query

Answer

A subquery is a query embedded within another SQL query, often in the WHERE, FROM, or SELECT clause.

Question 3

What does the GROUP BY clause do in SQL?

Accepted Answer

Aggregates rows sharing the same value in specified columns

Answer

GROUP BY collapses rows that have the same value in the specified column(s) so aggregate functions like SUM or COUNT apply per group.

Question 4

Which SQL join returns only the rows where there is a match in both tables?

Accepted Answer

INNER JOIN

Answer

INNER JOIN returns only rows that have matching values in both tables based on the join condition.

Question 5

What is the purpose of an index in a database?

Accepted Answer

Speed up data retrieval operations

Answer

An index creates a data structure that allows the database engine to locate rows faster without scanning the entire table.

DA - Data Analyst Practice Test