Mysql distinct null values

The output of COUNT in the last command shows count as 3 as against 6 which is against the expectation of the user. This is because, here we are counting the distinct records in columns and since NULL represents no value we cannot basically count something which is not present. Then why would the previous command does not show this behaviour? URL Name. A NULL value means that the field has no value present. For this, we will use the following query:. These values are passed to the count function which counts the number of unique values and returns the result-set as follows:.

Now, how about finding the total number of guests from each country? If you wish to do further reading, check out the articles mentioned in the References section below. Let us clarify our concept with the help of an example. Note that here position and technology togetherly should have unique values. We can observe from the developers table records that there are two records with names Payal and Heena having the same technology and same position i.

So, both these columns should be retrieved in only one record in the resultset of the following queries. While all other records represent distinct technology, position combination. That contains 11 records while the table contained 12 records as the two records named Heena and Payal had the same technology and position values of combination.

When GROUP BY clause is used on a single column and retrieved the column on which the group by clause is applied, it retrieves all the distinct values. Now, let us group the developers table based on the position column that will give us all the assigned positions list. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.

Stack Gives Back Safety in numbers: crowdsourcing data on nefarious IP addresses. Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually.

Linked 0. Related