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/

Answer 2

Here's one option using a subquery with DISTINCT:

SELECT COUNT(*) gender_count,
   SUM(IF(gender='male',1,0)) male_count,
   SUM(IF(gender='female',1,0)) female_count
FROM (
   SELECT DISTINCT tel, gender
   FROM example_dataset
) t

• SQL Fiddle Demo

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This will also work if you don't want to use a subquery:

SELECT COUNT(DISTINCT tel) gender_count,
    COUNT(DISTINCT CASE WHEN gender = 'male' THEN tel END) male_count,  
    COUNT(DISTINCT CASE WHEN gender = 'female' THEN tel END) female_count
FROM example_dataset

• More Fiddle