What is the result of count function in the NULL value present in DB2 table?

The COUNT function in DB2 is used to return the number of rows which satisfies the given criteria. The GROUP BY is used to divide the rows in the groups based on the criteria given in the query.

If we perform the GROUP BY on INVOICE_ID and there are few rows having NULL value in INVOICE_ID then the null values form a separate group. For example, if we have below table.

ORDER_ID	INVOICE_ID
A11234	3214
A55611	3214
A99867	NULL
A55671	3214
A88907	NULL
A56012	6701

On executing the query which performs GROUP BY on INVOICE_ID and counts the number of rows, we will get the result below.

SELECT INVOICE_ID, COUNT(*) AS INVOICE COUNT FROM ORDERS GROUP BY INVOICE_ID;

INVOICE_ID	INVOICE COUNT
3214	3
NULL	2
6701	1