DISTINCT for unique values in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the SQL keyword DISTINCT do?

It removes duplicate rows from the result set, showing only unique values.

beginner

How would you select unique city names from a table called Customers?

Use SELECT DISTINCT city FROM Customers; to get only unique city names.

intermediate

Can DISTINCT be used on multiple columns?

Yes, it returns unique combinations of the specified columns.

beginner

What happens if you use DISTINCT on a column with all unique values?

The result will be the same as a normal SELECT because all values are already unique.

intermediate

Is DISTINCT case sensitive when filtering unique values?

It depends on the database collation settings, but usually it is case insensitive in MySQL by default.

What does SELECT DISTINCT do in SQL?

A Counts the number of rows

B Deletes duplicate rows from the table

C Sorts the rows alphabetically

D Returns only unique rows

DISTINCT filters the result set to show only unique rows, without duplicates.

Which query returns unique combinations of city and state from Customers?

A SELECT DISTINCT city, state FROM Customers;

B SELECT city, state WHERE DISTINCT FROM Customers;

C SELECT UNIQUE city, state FROM Customers;

D SELECT city, state FROM Customers;

Only SELECT DISTINCT city, state FROM Customers; returns unique pairs of city and state.

If a column has all unique values, what effect does DISTINCT have?

A Removes all rows

B Duplicates the rows

C Returns the same result as SELECT

D Returns an error

DISTINCT will return the same rows because all values are already unique.

Can DISTINCT be used on multiple columns at once?

A Yes, it returns unique combinations of those columns

B No, only one column at a time

C Yes, but only if columns are numeric

D No, it causes a syntax error

DISTINCT works on multiple columns to return unique combinations of their values.

Is DISTINCT case sensitive in MySQL by default?

A Yes, always case sensitive

B No, usually case insensitive depending on collation

C It depends on the SELECT statement

D It causes an error if case differs

MySQL's default collation usually makes DISTINCT case insensitive.

Explain how the DISTINCT keyword works in SQL and give an example query.

Think about how you would find unique items in a list.

Describe what happens when you use DISTINCT on multiple columns in a SELECT statement.

Consider how two columns together create a unique pair.