Question

I am having trouble and need some help finding a correct SQL query. Here is my code so far:

SELECT firstname, lastname, date_of_birth 
  FROM `data` 
 WHERE firstname IN (SELECT firstname 
                       FROM `data` 
                      WHERE diagnosis_location = 'Mayo') 
   AND lastname IN (SELECT lastname 
                      FROM `data` 
                     WHERE diagnosis_location = 'Mayo') 
   AND date_of_birth IN (SELECT date_of_birth 
                           FROM `data` 
                          WHERE diagnosis_location = 'Mayo') 
   AND firstname IN (SELECT firstname 
                       FROM `data` 
                      WHERE diagnosis_location = 'Lahey') 
   AND lastname IN (SELECT lastname 
                      FROM `data` 
                     WHERE diagnosis_location = 'Lahey') 
   AND date_of_birth IN (SELECT date_of_birth 
                           FROM `data` 
                          WHERE diagnosis_location = 'Lahey')

Yes, it’s a monster of a query and probably isn’t all that efficient. But what I am trying to do is only return the first name, last name, and date of birth of all patients diagnosed at both the ‘Mayo’ location and the ‘Lahey’ location. This query does return those patients, but it returns multiple rows of the same exact data.

How could I limit it so duplicates of the same exact results are trimmed out?

Answer 1

Use:

  SELECT firstname, lastname, date_of_birth 
    FROM `data`
   WHERE diagnosis_location IN ('Mayo', 'Lahey')
GROUP BY firstname, lastname, date_of_birth 
  HAVING COUNT(DISTINCT diagnosis_location) = 2