Question

What is the difference between the following two SQL queries?

Option 1:
sql
Copy code
SELECT COUNT(*) FROM Student;
Option 2:
sql
Copy code
SELECT COUNT(age) FROM Student;
Option 3:
sql
Copy code
SELECT COUNT(DISTINCT *) FROM Student;
Option 4:
sql
Copy code
SELECT COUNT(DISTINCT age) FROM Student;

Answer 1

The difference in the SQL queries lies in what is being counted: all rows, non-null values, all distinct rows, or distinct values in a specific column.

Step-by-step explanation:

The difference between the two SQL queries lies in what is being counted. In Option 1, COUNT(*) is used to count all the rows in the 'Student' table, regardless of whether the 'age' column is null or not. In Option 2, COUNT(age) counts the number of non-null values in the 'age' column of the 'Student' table.

Option 3, COUNT(DISTINCT *), counts the number of distinct rows in the 'Student' table. It considers all columns in each row to determine uniqueness. Option 4, COUNT(DISTINCT age), counts the number of distinct values in the 'age' column.