表列合并查询

Question

我做了一个表查询是

CREATE TABLE questions (
     _id             INTEGER PRIMARY KEY AUTOINCREMENT
   , question        TEXT
   , correct_answer  TEXT    DEFAULT (null)
   , answer1         TEXT    DEFAULT (null)
   , answer2         TEXT    DEFAULT (null) 
   , answer3         TEXT    DEFAULT (null)
   , answer4         TEXT    DEFAULT (null)
   , difficulty      INTEGER DEFAULT (null) 
   , nid             INTEGER
);

现在想省略正确答案列，并在 answer1 列中做所有正确的答案，在 answer2,answer3,answer4 中做其他 3 个错误的答案。 但问题目前正确答案可能是四个中的任何一个，所以我无法合并

作为示例表就像

你可以在答案2的第一行看到正确答案，第二行的正确答案是在答案4

那么我如何分别在 answer1 列中选择正确答案，在 answer2、answer3、answer4 中分别获取其他错误答案？

什么是 sql 查询？ 或任何其他想法？

Answer 1

我会做这样的事情：

insert into question_new (_id, qestion, answer1, answer2, answer3, answer4)
SELECT _id, question, 
correct_answer as answer1, 
if (correct_answer = answer2 , answer1 , answer2) as answer2,
if (correct_answer = answer3 , answer1 , answer3) as answer3,
if (correct_answer = answer4 , answer1 , answer4) as answer4
 FROM questions

简单来说：

1. answer1 将始终是正确的答案列。
2. answer2/3/4 将是
   • 如果与正确答案不同，则为同一列（与默认表相同）
   • answer1 如果等于正确答案（在 answer1 中有正确答案，所以你需要在新位置设置错误的 answer1 ）

更新

添加相同的查询使用case when

insert into question_new (_id, qestion, answer1, answer2, answer3, answer4)
SELECT _id, question, 
correct_answer as answer1, 
case when correct_answer = answer2 then answer1 else answer2 end as answer2,
case when correct_answer = answer3 then answer1 else answer3 end as answer3,
case when correct_answer = answer4 then answer1  else answer4 end as answer4
 FROM questions

Answer 2

我会这样做

insert into questions2(_id, qestion, answer1, answer2, answer3, answer4)
select _id, question , correct_answer as answer1,
case when correct_answer = answer1 then answer2 else answer1 end answer2,
case when correct_answer = answer2 then answer3 else answer2 end answer3,
case when correct_answer = answer3 then answer4 else answer3 end answer4
from questions

所以你最终会得到一个新表格，其中包含你想要的格式的问题

Answer 3

你可以试试这个——

SELECT question, correct_answer,
CASE WHEN answer1 != correct_answer THEN answer1 ELSE answer2 END AS incorrect1,
CASE WHEN (answer1 != correct_answer AND answer2 != correct_answer) THEN answer2 ELSE answer3 END AS incorrect2,
CASE WHEN (answer1 != correct_answer AND answer2 != correct_answer AND answer3 != correct_answer) THEN answer3 ELSE answer4 END AS incorrect3
FROM questions

Answer 4

有点晚了，但您可以更新您的表，而无需辅助表根据需要存储数据

UPDATE questions

SET 
answer2 = CASE WHEN answer2 = correct_answer
          THEN answer1 ELSE answer2 END,

answer3 = CASE WHEN answer3 = correct_answer
          THEN answer1 ELSE answer3 END,

answer4 = CASE WHEN answer4 = correct_answer
          THEN answer1 ELSE answer4 END,
answer1 = correct_answer

在此处检查SQL FIDDLE