MySQL distinct count if conditions unique

Question

I am trying to build a query that tells me how many distinct women and men there are in a given dataset. The person is identified by a number \'tel\'. It is possible for the sam

Answer 1

There is another solution similar to @segeddes's second solution

Select COUNT(DISTINCT tel) as gender_count, 
       COUNT(DISTINCT IF(gender = "male", tel, NULL)) as male_count, 
       COUNT(DISTINCT IF(gender = "female", tel, NULL)) as female_count 
FROM example_dataset

Explanation :

IF(gender = "male", tel, NULL)

Above expression will return tel if gender is male else it will return NULL value

Then we've

DISTINCT

It will remove all the duplicates

And finally

COUNT(DISTINCT IF(gender = "male", tel, NULL))

Will count all the distinct occurrences of rows having male gender

Note : SQL COUNT function with expression only counts rows with non NULL values, for detailed explanation check - http://www.mysqltutorial.org/mysql-count/