LeetCode--578. 查询回答率最高的问题

建表

CREATE TABLE survey_log ( id INT, `action` VARCHAR(10), question_id INT, answer_id INT, q_num INT, TIMESTAMP INT ); INSERT INTO survey_log VALUES(5, 'show', 285, NULL, 1, 123); INSERT INTO survey_log VALUES(5, 'answer', 285, 124124, 1, 124); INSERT INTO survey_log VALUES(5, 'show', 369, NULL, 2, 125); INSERT INTO survey_log VALUES(5, 'skip', 369, NULL, 2, 126);

解题思路

对于每道题来说，不管被回答多少次，题目数量就是1，也就是分母是1， 那么将题目转化为求每道题被回答的次数，也就是answer_id不为NULL的次数

SELECT question_id survey_log FROM survey_log WHERE answer_id IS NOT NULL GROUP BY question_id ORDER BY COUNT(answer_id) DESC LIMIT 1