Wählen Sie die Differenz zwischen dem Höchst- und Mindestgewicht einer Person mit dem Nachnamen Maroni.

Question

SELECT weight AS weight_delta
from (select max(weight) 
      from patients 
      where last_name='Maroni')
      -
      (select min(weight) 
      from patients 
      where last_name='Maroni');

Answer 1

你想得太复杂了。无需任何子查询即可找到差异：

SELECT MAX(weight) - MIN(weight) AS weight_delta 
FROM patients WHERE last_name = 'Maroni';