Database facts & stats

Question 1

In a relational database, data is stored in rows and columns inside what?

Accepted Answer

Tables. Relational databases organize data in tables, with each row a record and each column a field.

Question 2

Which SQL command retrieves data from a table?

Accepted Answer

SELECT. SELECT reads data, while INSERT adds rows and UPDATE changes existing rows.

Question 3

Which SQL clause filters rows based on a condition?

Accepted Answer

WHERE. WHERE keeps only rows that meet a condition, such as WHERE age > 18.

Question 4

Which type of join returns only rows that have matching values in both tables?

Accepted Answer

INNER JOIN. An inner join returns only rows with a match in both tables; outer joins also keep unmatched rows.

Question 5

What is the main purpose of a database index?

Accepted Answer

To speed up finding rows. An index works like a book's index, letting the database find rows without scanning the whole table.

Question 6

Who proposed the relational model of data in 1970?

Accepted Answer

Edgar F. Codd. IBM researcher Edgar F. Codd described the relational model in a 1970 paper, the basis of SQL databases.

Question 7

In the ACID properties of database transactions, what does the I stand for?

Accepted Answer

Isolation. ACID stands for Atomicity, Consistency, Isolation and Durability.

The basics