SQL Hollow value differs from null

A lot of people have this problem. What is the difference between populating a null value in SQL and NULL

Now I'm going to share your thoughts with an example. Please give us your criticism and correct me.

Create a Time table

CREATE TABLE #temp (name VARCHAR (50))

Fill three information as follows:

INSERT into #temp
VALUES (NULL)
INSERT into #temp
VALUES (' Tom ')
INSERT into #temp
VALUES (")

Use the following syntax to query

SELECT COUNT (name) from #temp得到结果为2 clearly three records for the hair one less

The research and analysis revealed the following reasons:

A. Null value does not occupy memory space in SQL, and null value allocates memory space

Two. Sum of Count () in SQL, the null value is automatically ignored and a null value records a data.

SQL Hollow value differs from null