W3. SQL Select Distinct

Question 1

Q: What does the SQL SELECT DISTINCT statement do?

Answer 1

A: It returns only distinct (unique) values from a specified column.

Question 2

Q: Write an SQL query to select all distinct countries from the “Customers” table.

Answer 2

A: SELECT DISTINCT Country FROM Customers;

Question 3

Q: Why might you use the SELECT DISTINCT statement?

Answer 3

A: To list only the different (unique) values in a column that may contain duplicates.

Question 4

Q: What is the general syntax for the SELECT DISTINCT statement?

Answer 4

A: SELECT DISTINCT column1, column2, … FROM table_name;

Question 5

Q: What happens if you omit DISTINCT in a SELECT statement?

Answer 5

A: The query will return all values, including duplicates, from the specified column(s).

Question 6

Q: How can you count the number of distinct values in a column?

Answer 6

A: Use COUNT(DISTINCT column_name) in your query, e.g.,
SELECT COUNT(DISTINCT Country) FROM Customers;

Question 7

Q: Is COUNT(DISTINCT column_name) supported in Microsoft Access?

Answer 7

A: No, Microsoft Access does not support COUNT(DISTINCT column_name) directly.

Question 8

Q: How can you work around the lack of COUNT(DISTINCT column_name) support in MS Access?

Answer 8

A: Use a subquery: SELECT Count(*) AS DistinctCountries FROM (SELECT DISTINCT Country FROM Customers);