自然連接和左連接在一起在MySQL

Question

我有如下表

1. 問題 - > ID，question_data邀請，USER_ID
2. 用戶 - > ID，FNAME，LNAME
3. question_connect-> ID，question_id， USER_ID

我最初的查詢結果如下

select questions.id, questions.question_data, users.id, users.fname from questions, users where questions.user_id = users.id limit 30 

但在這裏，我想對這個問題的用戶數，所以我嘗試下面的查詢

select questions.id, questions.question_data, users.id, users.fname, count(questions_connect.id) from questions, users LEFT JOIN questions_connect ON `questions`.`id` = `questions_connect`.`question_id` where questions.user_id = users.id group by `questions_connect`.`id` limit 30 

這顯示錯誤

Unknown column 'questions.id' in 'on clause' 

SO才能讓1個通話與自然連接和左連接和如果是的話，我去哪裏錯了..？

Answer 1

使用顯式連接應排在你出去：

select questions.id, questions.question_data, users.id, users.fname, count(questions_connect.id) 
from questions 
join users on questions.user_id = users.id 
left join questions_connect on `questions`.`id` = `questions_connect`.`question_id` 
group by `questions_connect`.`id` 
limit 30 

你最好確定你所有的連接顯式地，儘量忘記存在隱式連接。

Answer 2

我相信你也不需要把報價上加入

ON questions.id = questions_connect.question_id