-- Database schema
| bool : name [ TEXT ] primary_key | person : name [ TEXT ] primary_key | disabled : name [ TEXT ] primary_key disabled.name = person.name | enlist : name [ TEXT ] enlist.name = person.name , organ [ TEXT ] | filed_for_bankrupcy : name [ TEXT ] primary_key filed_for_bankrupcy.name = person.name | longest_absense_from_school : name [ TEXT ] primary_key longest_absense_from_school.name = person.name , month [ INTEGER ] | male : name [ TEXT ] primary_key male.name = person.name | no_payment_due : name [ TEXT ] primary_key no_payment_due.name = person.name , bool [ TEXT ] no_payment_due.bool = bool.name | unemployed : name [ TEXT ] primary_key unemployed.name = person.name | enrolled : name [ TEXT ] enrolled.name = person.name , school [ TEXT ] , month [ INTEGER ] |
-- -- Calculate the number of students who are not disabled.

SELECT COUNT(CASE  WHEN T2.name IS NULL THEN T1.name END) AS "number" FROM person AS T1 LEFT JOIN disabled AS T2 ON T2.name = T1.name;