mysql - 需要帮助在 mySQL 中返回唯一结果

Question

我遇到了麻烦，需要一些帮助来找到正确的 SQL 查询。到目前为止，这是我的代码:

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')

是的，这是一个庞大的查询，而且可能效率不高。但我想做的只是返回在“Mayo”地点和“Lahey”地点诊断出的所有患者的名字、姓氏和出生日期。此查询确实会返回那些患者，但会返回多行完全相同的数据。

我如何限制它，以便删除完全相同的结果的重复项？

Answer 1

使用:

  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