Mysql 在SELECT Case语句中合并行

我有这个疑问

SELECT questions.question_id, 
       questions.question, 
       questions.answer_id, 
       nlp_terms.word,
       ( CASE 
           WHEN answers.id = questions.answer_id THEN answers.answer 
         END ) AS answer, 
       ( CASE 
           WHEN answers.id != questions.answer_id THEN answers.answer 
         END ) AS incorrect_answer_1, 
       ( CASE 
           WHEN answers.id != questions.answer_id THEN answers.answer 
         END ) AS incorrect_answer_2 
FROM   questions 
       JOIN answers 
         ON answers.question_id = questions.question_id 
       JOIN nlp_terms 
         ON questions.question_id = nlp_terms.question_id
WHERE questions.question_id = '1'

此查询输出：

╔═════════════╦═══════════════════════════════════════════╦═══════════╦═══════════╦════════╦════════════════════╦════════════════════╗
║ question_id ║                 question                  ║ answer_id ║   word    ║ answer ║ incorrect_answer_1 ║ incorrect_answer_2 ║
╠═════════════╬═══════════════════════════════════════════╬═══════════╬═══════════╬════════╬════════════════════╬════════════════════╣
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ What      ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ continent ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ is        ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ the       ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ country   ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ Lesotho   ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ in?       ║ NULL   ║ South America      ║ South America      ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ What      ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ continent ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ is        ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ the       ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ country   ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ Lesotho   ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ in?       ║ Africa ║ NULL               ║ NULL               ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ What      ║ NULL   ║ Australia          ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ continent ║ NULL   ║ Australia          ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ is        ║ NULL   ║ Australia          ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ the       ║ NULL   ║ Australia          ║ AustraliA          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ country   ║ NULL   ║ Australia          ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ Lesotho   ║ NULL   ║ Australia          ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ in?       ║ NULL   ║ Australia          ║ Australia          ║
╚═════════════╩═══════════════════════════════════════════╩═══════════╩═══════════╩════════╩════════════════════╩════════════════════╝

正如您所看到的，它带来了我想要的所有数据，只是我的CASE语句采用了它们自己的一行，而不是分组

我进行了大量的

分组操作，但无法使其与我的预期输出相同：

╔═════════════╦═══════════════════════════════════════════╦═══════════╦═══════════╦════════╦════════════════════╦════════════════════╗
║ question_id ║                 question                  ║ answer_id ║   word    ║ answer ║ incorrect_answer_1 ║ incorrect_answer_2 ║
╠═════════════╬═══════════════════════════════════════════╬═══════════╬═══════════╬════════╬════════════════════╬════════════════════╣
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ What      ║ Africa ║ South America      ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ continent ║ Africa ║ South America      ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ is        ║ Africa ║ South America      ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ the       ║ Africa ║ South America      ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ country   ║ Africa ║ South America      ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ Lesotho   ║ Africa ║ South America      ║ Australia          ║
║        1369 ║ What continent is the country Lesotho in? ║      4106 ║ in?       ║ Africa ║ South America      ║ Australia          ║
╚═════════════╩═══════════════════════════════════════════╩═══════════╩═══════════╩════════╩════════════════════╩════════════════════╝

要获得预期的输出，我缺少什么？
我认为这会产生您想要的结果：

SELECT q.question_id, q.question, q.answer_id, t.word,
       MAX(CASE WHEN a.id = q.answer_id THEN a.answer 
           END) AS answer, 
       MAX(CASE WHEN a.id <> q.answer_id THEN a.answer 
           END) AS incorrect_answer_1, 
       MIN(CASE WHEN a.id <> q.answer_id THEN a.answer 
           END) AS incorrect_answer_2 
FROM questions q JOIN
     answers a
     ON a.question_id = q.question_id JOIN
     nlp_terms t
     ON q.question_id = t.question_id
WHERE q.question_id = 1
GROUP BY q.question_id, q.question, q.answer_id, t.word;

选择q.question\u id、q.question、q.answer\u id、t.word、，
最大值（a.id=q.answer\u id然后a.answer时的情况）
(完)作为回答,，
最大值（a.id q.answer\u id然后a.answer时的情况）
结束）由于回答不正确，
最小值（a.id q.answer\u id然后a.answer时的情况
结束）因为回答不正确
从问题q连接
回答a
关于a.question\u id=q.question\u id连接
nlp_术语
关于q.question\u id=t.question\u id
其中q.question_id=1
按q.question\u id、q.question、q.answer\u id、t.word分组；
您是否尝试过“WHERE questions.question\u id='1'且答案不为空”

参考资料：
您所有的问题都只有3个答案吗？现在，是的，所有问题都有3个答案。结果相同。谢谢，是的！我爱你，谢谢。进行编辑
MIN（q.id
时的情况应为
MIN（q.question\u id
时的情况，假设我必须引入
nlp\u terms.id
自动增量（
t.id
）为了确保单词的顺序也正确？当我添加它时效果很好，因为上面的答案查询是按
t排序的。word
alphalcomcally你实际上在我面前发现了它（我的意思是不奇怪：），但我没有重新阅读整个更新以注意到）-查看更多关于它的
MIN（我之前评论过的CASE
完全不应该引用表q，事实上，在所有的
CASE
语句中都应该是
a.id
到
q.question\u id
。正如上面提到的那样，包含
GROUP BY
t.id
并以
顺序
BY
t.id
结束查询tput工作完美。再次感谢您分享您在这方面的知识和见解。我正在变得更好，您在我记事之前帮助了我。