Calculate the percentage of people who were born after 1970 and from California.
born after 1970 refers to birthdate > 1970; from California refers to birth_region = 'California'; percentage = divide(count(birthdate > 1970 and birth_region = 'California'), total(birthdate)) * 100%
SELECT CAST(SUM(CASE WHEN birth_region = 'California' AND SUBSTR(birthdate, 1, 4) > '1970' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(birthdate) FROM Person;