W3. SQL Count

Question 1

Q: What does the SQL COUNT() function do?

Answer 1

A: It returns the number of rows that match a specified criterion.

Question 2

Q: Write a query to find the total number of rows in the “Products” table.

Answer 2

SELECT COUNT(*) 
FROM Products;

Question 3

Q: What is the difference between COUNT(*) and COUNT(column_name)?

Answer 3

A: COUNT(*) counts all rows, including NULL values, while COUNT(column_name) only counts non-NULL values in the specified column.

Question 4

Q: Write a query to find the number of products where ProductName is not NULL.

Answer 4

SELECT COUNT(ProductName) 
FROM Products;

Question 5

Q: How can you use the WHERE clause with COUNT()?

Answer 5

A: Add a condition in WHERE to specify the rows to count, e.g., WHERE Price > 20.

Question 6

Q: Write a query to count the products with a Price greater than 20.

Answer 6

SELECT COUNT(ProductID) 
FROM Products 
WHERE Price > 20;

Question 7

Q: How do you ignore duplicates in COUNT()?

Answer 7

A: Use COUNT(DISTINCT column_name) to count only unique values.

Question 8

Q: Write a query to count the number of different prices in the “Products” table.

Answer 8

SELECT COUNT(DISTINCT Price) 
FROM Products;

Question 9

Q: How can you give the counted column a descriptive name?

Answer 9

A: Use the AS keyword to set an alias, e.g., AS [Number of records].

Question 10

Q: Write a query to count all records in the “Products” table and label the count as “Number of records.”

Answer 10

SELECT COUNT(*) AS [Number of records] 
FROM Products;

Question 11

Q: How do you use COUNT() with GROUP BY?

Answer 11

A: Combine COUNT() with GROUP BY to return the count for each group, e.g., GROUP BY CategoryID.

Question 12

Q: Write a query to count the number of records for each category in the “Products” table.

Answer 12

SELECT COUNT(*) AS [Number of records], CategoryID 
FROM Products 
GROUP BY CategoryID;