Online Coding Lessons SQL and Database Basics 2

Question 1

Which SQL keyword removes duplicate rows from a SELECT result?

Accepted Answer

DISTINCT

Answer

The DISTINCT keyword, used right after SELECT, eliminates duplicate rows so each value appears only once in the results.

Question 2

What SQL clause is used to combine rows from two or more tables based on a related column?

Accepted Answer

JOIN

Answer

The JOIN clause is used to combine rows from two or more tables based on a related (usually matching) column between them.

Question 3

Which SQL aggregate function returns the total number of rows in a result set?

Accepted Answer

COUNT()

Answer

COUNT() is an aggregate function that returns the number of rows that match a specified condition.

Question 4

What does the UPDATE command do in SQL?

Accepted Answer

Changes existing data in one or more rows

Answer

The UPDATE statement modifies the values of existing records in a table, usually with a WHERE clause to target specific rows.

Question 5

In SQL, what does the wildcard character % represent when used with the LIKE operator?

Accepted Answer

Any sequence of zero or more characters

Answer

The % wildcard in a LIKE pattern matches any sequence of zero or more characters, making it useful for partial-text searches.

Online Coding Lessons Practice Test