count() function

Hi Peter!
Thanks for reaching out.
In order to count the null values, you can use the following code:
SELECT
    COUNT(IF(column_name IS NULL, 1, 0))
FROM
    table_name;

Hope this helps.
Best,
Tsvetelin

Thank you Tsvetelin Tsankov for your response, Can you explain why you put 1 and 0  at the end     COUNT(IF(column_name IS NULL, 1, 0))

Hi Peter,

It's for the IF conditional statement.
IF statement works by creating a column, say A, then put values in it based on whether a condition is satisfied or not. In your case, the values of column A will based on a condition applied to column_name. If it's NULL, then we assign a value of 1. Otherwise, we assign a value of 0.

Then, the COUNT function will run, counting all the rows of column A with a value of 1. Since those 1's correspond to NULL values of column_name, you also get the number of those NULL values.

Hi Peter!
Thanks for reaching out.

Carl explained it very well. The COUNT() function will count all the rows of column A with a
value of 1. Since those 1's correspond to NULL values of column_name, you also get the number of those NULL values.

Hope this helps.
Best,
Tsvetelin

I tried this code, it worked but I feel like something is wrong since the results showed 300,024 count

SELECT
COUNT(IF(birth_date is null, 1, 0))
FROM
employees;

what could be wrong with it?

its true the if statement didn't work so instead use the count(*) with the where IS NULL  to count all the null values

SELECT 
    COUNT(*)
FROM
    employees
WHERE
    first_name IS NULL; 

The Purpose:

This function is designed to specifically count the number of NULL (empty or missing) values within a column of data.

How It Works:

IF(column_name IS NULL, 1, 0) : This part checks each cell in the column you've specified ('column_name').
If the cell is NULL (empty), it assigns a value of "1".
If the cell is NOT NULL (has data), it assigns a value of "0".
COUNT(): This outer function counts all the occurrences of "1". Since each "1" represents a NULL cell, you get a direct count of how many empty cells there are in the column.
 

Think of it like this:

You have a basket of fruit. Some are ripe, some are missing.
You want to know exactly how many pieces of fruit are missing.
You put a sticker on each missing fruit (sticker = "1").
You ignore the ripe fruit (they get "0").
Finally, you count only the stickers to find out how many pieces of fruit were missing.