Question

我尝试根据第一张表格中字段的前4个字符加入第二张表，但我不断收到＆＃34; Unknown column＆＃39; questions.first4＆＃39;在＆＃39; on条款＆＃39;＆＃34;而且我不确定原因：

SELECT questions.id as id, question, answer, correct, SUBSTRING(question,1,4) as first4
FROM questions
LEFT JOIN answers ON answers.correct_answer = questions.first4
WHERE player_name = 'Alpha Squad'
ORDER BY id ASC

（我意识到这些表的结构效率很低，但不幸的是，我必须按原样使用它们）

表：https://pastebin.com/Gur5ufXa

MySQL：https://pastebin.com/FLgWtQmY

提前致谢！

Answer 1

SELECT questions.id as id, question, answer, correct, SUBSTRING(question,1,4) as first4
FROM questions
LEFT JOIN answers ON answers.correct_answer = questions.correct
WHERE player_name = 'Alpha Squad'
ORDER BY id ASC

或者下一个特别加入具有匹配的前4个

的那个

SELECT questions.id as id, question, answer, correct, SUBSTRING(question,1,4) as first4
    FROM questions
    LEFT JOIN answers ON SUBSTRING(answers.correct_answer,1,4) = SUBSTRING(question,1,4)
    ORDER BY id ASC

Answer 2

SELECT questions.id as id, question, answer, correct, SUBSTRING(question,1,4) as first4
FROM questions
LEFT JOIN answers ON answers.correct_answer = SUBSTRING(question,1,4) 
WHERE player_name = 'Alpha Squad'
ORDER BY id ASC

问题是在尝试进行JOIN时，first4不存在。点击此处查看处理选择状态的订单。

Order Of Execution of the SQL query

MySQL连接基于前4个字符

2 个答案: