1

I have the following query:

SELECT DISTINCT name, surname, id_number, gender FROM table1;

How do I filter by gender to get the gender breakdown of the results of the above query? Do I use a subquery? If so, how do I write the subquery?

Note in my table there are duplicate entries for id_number

Sample Data:

-------------------------------------
Name    | Surname   |ID_No   |Gender|
-------------------------------------
John       Doe        1234A6    M
Jane       Doe        2553B7    F
Steve      Jobs       2636A8    M

Expected Output

--------------
  M   |   F  |
---------------
  2       1
  • Is id_number not already unique? Do you have duplicate id_numbers in the table? – Evan Carroll Dec 18 '18 at 14:48
  • @EvanCarroll, yes I have duplicate id_numbers in the table – Lodza Wa Mampela Dec 18 '18 at 14:51
0

If id_number is not UNIQUE (by extension) nor a PRIMARY KEY what you want is COUNT(DISTINCT ...)

SELECT
    gender, count(DISTINCT name, surname, id_number)
FROM table1
GROUP BY gender;

And you want either,

  • an index on gender, and a second index on name, surname, id_number
  • an index on gender, name, surname, id_number

No guarantee that MySQL will do something smart with them anyway, but it'll use them for the first sorting into Male/Female which will at the least reduce the DISTINCT load by ~1/2. As compare to the current answer which may double it.

0

I'm pretty sure that this will work for you. I don't have a MySQL instance available to me to check my syntax, but this should get you close.

SELECT gender, COUNT(id_number)
FROM (  SELECT DISTINCT
            name
            , surname
            , id_number
            , gender
        FROM table1
        ) AS D
GROUP BY gender; 

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