Does the SQL COUNT function automatically exclude NULL values?

Question

I have a database called people with a total of 8398 records. I know this because I have performed the following query with the COUNT function.

SELECT COUNT(*)
FROM people;

However, when I perform a COUNT on the birthdate column I find that this only returns 6152 records. Is this because the COUNT function is automatically excluding NULL values in the birthdate column?

SELECT COUNT(birthdate)
FROM people;

How could I perform a count of all the columns that are NULL in the birthday column?

Answer 1

How could I perform a count of all the columns that are NULL in the birthday column?

Check if column is null using CASE expression:

SELECT COUNT(CASE WHEN birthdate IS NULL THEN 1 END)
FROM people;

The expression evaluates to 1 when birthdate is null, and evaluates to NULL when brthdate is not null. Since COUNT counts only not null values, you will get a number of NULLs in birthdate column.

Answer 2

please check this solution its might be helpful..

SELECT COUNT(CASE WHEN birthdate IS NULL THEN 1 END) FROM people;