MYSQL <> 运算符代替 NOT IN

Question

如何使用 <> 做出这个答案而不是NOT IN

SELECT ward_no, COUNT(patient_id) AS occupying
FROM patient
WHERE ward_no NOT IN ('w5', 'w7')
GROUP BY ward_no

Answer 1

你可以这样做:

SELECT ward_no, COUNT(patient_id) AS occupying
FROM patient
WHERE ward_no <> 'w5' AND ward_no <> 'w7'
GROUP BY ward_no

但它比简单的 NOT IN 重得多，所以我自己不会这样做。