我有一个这个数据库的测验应用程序，我被要求打印正确的答案，即考试密钥和每个用户的答案，但如果用户留下任何答案空白，它应该是null或'x'或任何东西认识到这一点。
每个问题都有几个干扰者（选项），但只有一个是正确的（distractors.correct = 1），只有一个答案（answers.question_id），并检查答案是否正确answers.answer = distractor.option。 需要的输出：
+-----------+---------------+----------+-----------+---------------+-----------+----------+
| exam_id | question_id | option | correct | question_id | user_id | answer |
|-----------+---------------+----------+-----------+---------------+-----------+----------|
| 195 | 41303 | E | 0 | 41303 | 4404 | null |
| 195 | 41483 | A | 0 | 41483 | 4404 | A |
| 195 | 41350 | A | 0 | 41350 | 4404 | A |
| 195 | 41401 | E | 0 | 41401 | 4404 | E |
| 195 | 41271 | A | 0 | 41271 | 4404 | A |
| 195 | 41448 | D | 1 | 41448 | 4404 | D |
| 195 | 41320 | E | 1 | 41320 | 4404 | E |
| 195 | 41499 | C | 1 | 41499 | 4404 | C |
| 195 | 41369 | C | 1 | 41369 | 4404 | null |
| 195 | 41418 | E | 0 | 41418 | 4404 | E |
| 195 | 41287 | D | 1 | 41287 | 4404 | D |
| 195 | 41467 | B | 1 | 41467 | 4404 | B |
| 195 | 41337 | C | 1 | 41337 | 4404 | C |
| 195 | 41385 | E | 0 | 41385 | 4404 | E |
预期客户结果。
key DBCCDBCCABDBBADCBCCDDCCADBACDCBACCCDDBDDADAAACCACADBDCBBDDDADABBACDADCBDABADCCAACCBBBABBACAAADXADCAABBBBCDDADCCBDBACDCABDABDACACAC
0001 DBCCBBCCBBBBBADBXXXXDCBABBACDCBACCCDDBDCADAAABCAADCBDCBBDDDDDCBBACDABCBDDBACACAACCBBBAABACABDDBCDCBABCBBCDDADCCBDBACDCDCDBDBCCACAC
0002 DACCBBCCCBDDBAACBCCDCBBABAABDCBACCCDDBDCACAAACCADABBDCBCADDDDABBBCAADCBDABACCCABBDCDBDCDADABBDDBACBABBDBDDDADCCBDBABBCDBDADBBCACAB
0003 CCCCCBCCBBDCBBDCBCCADCAABAAADCBABCCDCCDCADAAABCADABBCCBBBDBADABBACDADCBAABACBCCCCDCDCAADACABADBCCCBABBDDCDDDDCCBBBACDCDBDDBBACADAC
0004 CCDACBCCBBDDBADBBCCBABBADBACDCBACCCDDCDCADAAACCADADBDCBADDDDDABBACAACCBCACACCCAACCBBBAAAACABBDAACCCABBDBCDDADCCBDBACDCACBADCCCACAC
0005 CCDCCBCCABDDBADCBCCCDCBACBABDCBACCCDDBDCADAAABDDDDDDDABADDDBDABBACDAACBDACADDCCACCBBBACBACADADBADCBABBABCDDADCCBDBACDCADDBDBACADAC
0006 CCCCCBCCABDDCADCBCDCDCAACBACDCBABACDDBDCADAADCCADACCAABABDDBDABBACDABCADABADAACACCDBBABBACADBDCADCAACBDBCDDADCCBDBABDCABDABBBBDCAC
我知道这将包含一个我不需要的转置因为我将在数组/集合中处理php中的结果。 第一行有所有正确的答案/选项 下一行有每个用户的答案。
试过这个：
select answers.exam_id, distractors.question_id, distractors.option, distractors.correct, answers.question_id, answers.user_id, answers.answer
from distractors
LEFT JOIN answers on distractors.question_id = answers.question_id
AND answers.answer = distractors.option
AND answers.user_id = 4404
WHERE answers.exam_id = 195
ORDER BY answers.user_id
;
+-----------+---------------+----------+-----------+---------------+-----------+----------+
| exam_id | question_id | option | correct | question_id | user_id | answer |
|-----------+---------------+----------+-----------+---------------+-----------+----------|
| 195 | 41263 | C | 1 | 41263 | 4404 | C |
| 195 | 41259 | C | 0 | 41259 | 4404 | C |
| 195 | 41260 | E | 0 | 41260 | 4404 | E |
| 195 | 41261 | B | 0 | 41261 | 4404 | B |
| 195 | 41262 | E | 0 | 41262 | 4404 | E |
| 195 | 41264 | C | 1 | 41264 | 4404 | C |
| 195 | 41265 | E | 1 | 41265 | 4404 | E |
| 195 | 41266 | A | 0 | 41266 | 4404 | A |
| 195 | 41267 | A | 0 | 41267 | 4404 | A |
| 195 | 41268 | A | 1 | 41268 | 4404 | A |
| 195 | 41269 | E | 0 | 41269 | 4404 | E |
| 195 | 41270 | B | 0 | 41270 | 4404 | B |
| 195 | 41271 | A | 0 | 41271 | 4404 | A |
| 195 | 41272 | C | 0 | 41272 | 4404 | C |
| 195 | 41273 | E | 0 | 41273 | 4404 | E |
| 195 | 41274 | A | 0 | 41274 | 4404 | A |
| 195 | 41275 | E | 0 | 41275 | 4404 | E |
| 195 | 41276 | C | 0 | 41276 | 4404 | C |
| 195 | 41277 | D | 1 | 41277 | 4404 | D |
| 195 | 41278 | D | 0 | 41278 | 4404 | D |
| 195 | 41279 | C | 1 | 41279 | 4404 | C |
| 195 | 41280 | B | 1 | 41280 | 4404 | B |
| 195 | 41282 | D | 0 | 41282 | 4404 | D |
| 195 | 41281 | E | 1 | 41281 | 4404 | E |
| 195 | 41283 | D | 0 | 41283 | 4404 | D |
| 195 | 41284 | D | 1 | 41284 | 4404 | D |
| 195 | 41285 | E | 1 | 41285 | 4404 | E |
| 195 | 41286 | C | 1 | 41286 | 4404 | C |
| 195 | 41287 | D | 1 | 41287 | 4404 | D |
| 195 | 41288 | A | 1 | 41288 | 4404 | A |
| 195 | 41290 | C | 1 | 41290 | 4404 | C |
| 195 | 41289 | B | 1 | 41289 | 4404 | B |
| 195 | 41291 | E | 1 | 41291 | 4404 | E |
| 195 | 41292 | B | 1 | 41292 | 4404 | B |
| 195 | 41293 | C | 1 | 41293 | 4404 | C |
| 195 | 41294 | D | 1 | 41294 | 4404 | D |
| 195 | 41296 | A | 0 | 41296 | 4404 | A |
| 195 | 41295 | C | 1 | 41295 | 4404 | C |
| 195 | 41297 | E | 0 | 41297 | 4404 | E |
| 195 | 41298 | C | 0 | 41298 | 4404 | C |
| 195 | 41299 | E | 0 | 41299 | 4404 | E |
| 195 | 41300 | B | 0 | 41300 | 4404 | B |
| 195 | 41301 | A | 1 | 41301 | 4404 | A |
| 195 | 41302 | B | 0 | 41302 | 4404 | B |
| 195 | 41303 | E | 0 | 41303 | 4404 | E |
| 195 | 41511 | A | 0 | 41511 | 4404 | A |
| 195 | 41512 | C | 0 | 41512 | 4404 | C |
| 195 | 41513 | B | 1 | 41513 | 4404 | B |
+-----------+---------------+----------+-----------+---------------+-----------+----------+
245 rows in set
没有得到预期的321个问题/答案以及随附的空值。
我尝试了几个连接，但没有一个给出预期的结果。
表格：
DESCRIBE answers;
+-------------+------------------+--------+-------+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
|-------------+------------------+--------+-------+-----------+----------------|
| id | int(10) unsigned | NO | PRI | <null> | auto_increment |
| user_id | int(10) unsigned | NO | MUL | <null> | |
| question_id | int(10) unsigned | NO | MUL | <null> | |
| answer | char(255) | YES | | <null> | |
| created_at | timestamp | YES | | <null> | |
| updated_at | timestamp | YES | | <null> | |
| deleted_at | timestamp | YES | | <null> | |
| exam_id | int(10) unsigned | NO | | <null> | |
+-------------+------------------+--------+-------+-----------+----------------+
8 rows in set
Time: 0.006s
DESCRIBE questions;
+------------+------------------+--------+-------+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
|------------+------------------+--------+-------+-----------+----------------|
| id | int(10) unsigned | NO | PRI | <null> | auto_increment |
| slot_id | int(10) unsigned | NO | MUL | <null> | |
| order | smallint(6) | NO | | <null> | |
| text | text | NO | | <null> | |
| created_at | timestamp | YES | | <null> | |
| updated_at | timestamp | YES | | <null> | |
+------------+------------------+--------+-------+-----------+----------------+
6 rows in set
Time: 0.008s
DESCRIBE distractors;
+-------------+------------------+--------+-------+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
|-------------+------------------+--------+-------+-----------+----------------|
| id | int(10) unsigned | NO | PRI | <null> | auto_increment |
| question_id | int(10) unsigned | NO | MUL | <null> | |
| option | varchar(255) | NO | | <null> | |
| distractor | text | NO | | <null> | |
| correct | tinyint(1) | NO | | <null> | |
| created_at | timestamp | YES | | <null> | |
| updated_at | timestamp | YES | | <null> | |
+-------------+------------------+--------+-------+-----------+----------------+
7 rows in set
Time: 0.006s
describe exams;
+---------------+------------------+--------+-------+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
|---------------+------------------+--------+-------+-----------+----------------|
| id | int(10) unsigned | NO | PRI | <null> | auto_increment |
| applicated_at | datetime | NO | | <null> | |
| board_id | int(10) | NO | | <null> | |
| active | tinyint(1) | NO | | 1 | |
| duration | int(10) unsigned | NO | | <null> | |
| passing_grade | int(10) | YES | | <null> | |
| annotation | text | NO | | <null> | |
| deleted_at | timestamp | YES | | <null> | |
| created_at | timestamp | YES | | <null> | |
| updated_at | timestamp | YES | | <null> | |
+---------------+------------------+--------+-------+-----------+----------------+
10 rows in set
Time: 0.014s
示例数据：
select * from distractors limit 1000;
+------+---------------+----------+--------------------------------------------------------------------------------------------------------+-----------+---------------------+---------------------+
| id | question_id | option | distractor | correct | created_at | updated_at |
|------+---------------+----------+--------------------------------------------------------------------------------------------------------+-----------+---------------------+---------------------|
| 1 | 1 | A | Diuresis osmótica | 0 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 2 | 1 | B | Diabetes insípida central | 1 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 3 | 1 | C | Diabetes insípida nefrogénica | 0 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 4 | 1 | D | Administración de soluciones hipertónicas | 0 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 5 | 1 | E | Sx de secreción inapropiada de hormona antidiurética | 0 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 6 | 2 | A | TC cerebral | 0 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 7 | 2 | B | Sodio urinario | 0 | 2017-01-12 21:20:29 | 2017-01-12 21:20:29 |
| 8 | 2 | C | Osmolaridad sérica | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 9 | 2 | D | Osmolaridad urinaria | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 10 | 2 | E | Respuesta a vasopresina | 1 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 11 | 3 | A | Pérdida extrarrenal de agua | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 12 | 3 | B | Aumento en la reabsorción de sodio | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 13 | 3 | C | Aumento en la depuración de agua libre | 1 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 14 | 3 | D | Disminución en la depuración de agua libre | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 15 | 3 | E | Resistencia tubular a la acción de la hormona antidiurética | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 16 | 4 | A | Solución Hartmann | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 17 | 4 | B | Solución salina al 3% | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 18 | 4 | C | Solución salina al 0.9% | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 19 | 4 | D | Solución glucosada al 5 % | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 20 | 4 | E | Solución isotónica con HCO<sub>3</sub> | 1 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 21 | 5 | A | Mielinólisis | 0 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
| 22 | 5 | B | Edema cerebral | 1 | 2017-01-12 21:20:30 | 2017-01-12 21:20:30 |
select * from distractors limit 1000
+------+-----------+---------------+----------+---------------------+---------------------+--------------+-----------+
| id | user_id | question_id | answer | created_at | updated_at | deleted_at | exam_id |
|------+-----------+---------------+----------+---------------------+---------------------+--------------+-----------|
| 26 | 2782 | 1 | B | 2017-01-14 15:20:39 | 2017-01-14 15:20:39 | <null> | 1 |
| 27 | 2755 | 1 | B | 2017-01-14 15:20:39 | 2017-01-14 15:20:39 | <null> | 1 |
| 28 | 2741 | 1 | B | 2017-01-14 15:20:42 | 2017-01-14 15:20:42 | <null> | 1 |
| 29 | 2755 | 2 | E | 2017-01-14 15:20:51 | 2017-01-14 15:20:51 | <null> | 1 |
| 30 | 2755 | 3 | C | 2017-01-14 15:21:11 | 2017-01-14 15:21:11 | <null> | 1 |
| 31 | 2755 | 4 | D | 2017-01-14 15:21:25 | 2017-01-14 15:21:25 | <null> | 1 |
| 32 | 2741 | 2 | E | 2017-01-14 15:21:34 | 2017-01-14 15:21:34 | <null> | 1 |
| 33 | 2763 | 1 | B | 2017-01-14 15:21:39 | 2017-01-14 15:21:39 | <null> | 1 |
| 34 | 2782 | 4 | D | 2017-01-14 15:21:40 | 2017-01-14 15:21:40 | <null> | 1 |
| 35 | 2755 | 5 | B | 2017-01-14 15:21:52 | 2017-01-14 15:21:52 | <null> | 1 |
| 36 | 2782 | 5 | B | 2017-01-14 15:22:06 | 2017-01-14 15:22:06 | <null> | 1 |
| 37 | 2763 | 2 | D | 2017-01-14 15:22:07 | 2017-01-14 15:22:07 | <null> | 1 |
| 38 | 2775 | 116 | E | 2017-01-14 15:22:19 | 2017-01-14 15:22:19 | <null> | 1 |
| 39 | 2775 | 117 | A | 2017-01-14 15:22:23 | 2017-01-14 16:59:31 | <null> | 1 |
| 40 | 2801 | 21 | B | 2017-01-14 15:22:25 | 2017-01-14 15:22:25 | <null> | 1 |
| 41 | 2775 | 118 | A | 2017-01-14 15:22:29 | 2017-01-14 15:22:29 | <null> | 1 |
| 42 | 2868 | 301 | C | 2017-01-14 15:22:30 | 2017-01-14 15:22:47 | <null> | 2 |
| 43 | 2763 | 3 | C | 2017-01-14 15:22:36 | 2017-01-14 15:22:36 | <null> | 1 |
| 44 | 2775 | 119 | D | 2017-01-14 15:22:37 | 2017-01-14 15:22:37 | <null> | 1 |
| 45 | 2801 | 22 | C | 2017-01-14 15:22:40 | 2017-01-14 15:22:40 | <null> | 1 |
| 46 | 2734 | 1 | B | 2017-01-14 15:22:41 | 2017-01-14 15:22:41 | <null> | 1 |
| 47 | 2799 | 16 | C | 2017-01-14 15:22:41 | 2017-01-14 15:22:41 | <null> | 1 |
| 48 | 2782 | 2 | D | 2017-01-14 15:22:48 | 2017-01-14 15:25:11 | <null> | 1 |
| 49 | 2798 | 1 | B | 2017-01-14 15:22:51 | 2017-01-14 15:22:51 | <null> | 1 |
| 50 | 2803 | 21 | B | 2017-01-14 15:22:51 | 2017-01-14 15:22:51 | <null> | 1 |
| 51 | 2795 | 36 | B | 2017-01-14 15:22:54 | 2017-01-14 15:22:54 | <null> | 1 |
| 52 | 2803 | 22 | C | 2017-01-14 15:22:54 | 2017-01-14 15:22:54 | <null> | 1 |
| 53 | 2781 | 41 | D | 2017-01-14 15:22:59 | 2017-01-14 15:22:59 | <null> | 1 |
| 54 | 2862 | 321 | B | 2017-01-14 15:23:01 | 2017-01-14 15:23:01 | <null> | 2 |
| 55 | 2764 | 31 | A | 2017-01-14 15:23:01 | 2017-01-14 15:23:01 | <null> | 1 |
| 56 | 2769 | 21 | B | 2017-01-14 15:23:02 | 2017-01-14 15:23:02 | <null> | 1 |
| 57 | 2755 | 6 | A | 2017-01-14 15:23:02 | 2017-01-14 15:23:03 | <null> | 1 |
| 58 | 2871 | 302 | A | 2017-01-14 15:23:03 | 2017-01-14 15:27:40 | <null> | 2 |
| 59 | 2803 | 24 | E | 2017-01-14 15:23:03 | 2017-01-14 15:23:03 | <null> | 1 |
| 60 | 2868 | 302 | C | 2017-01-14 15:23:04 | 2017-01-14 15:23:04 | <null> | 2 |
| 61 | 2862 | 322 | E | 2017-01-14 15:23:13 | 2017-01-14 15:23:13 | <null> | 2 |
| 62 | 2799 | 17 | C | 2017-01-14 15:23:15 | 2017-01-14 15:23:15 | <null> | 1 |
| 63 | 2769 | 22 | C | 2017-01-14 15:23:16 | 2017-01-14 15:23:16 | <null> | 1 |
| 64 | 2741 | 3 | C | 2017-01-14 15:23:17 | 2017-01-14 15:23:17 | <null> | 1 |
select * from exams;
+------+---------------------+------------+----------+------------+-----------------+-----------------------------------------------------------------+--------------+---------------------+---------------------+
| id | applicated_at | board_id | active | duration | passing_grade | annotation | deleted_at | created_at | updated_at |
|------+---------------------+------------+----------+------------+-----------------+-----------------------------------------------------------------+--------------+---------------------+---------------------|
| 1 | 2017-01-14 09:00:00 | 32 | 1 | 180 | <null> | | <null> | 2017-01-12 21:22:08 | 2017-01-12 21:22:08 |
| 2 | 2017-01-14 09:05:00 | 32 | 1 | 180 | <null> | | <null> | 2017-01-12 21:25:14 | 2017-01-12 21:25:14 |
| 12 | 2017-01-19 16:00:00 | 13 | 1 | 180 | 120 | | <null> | 2017-01-17 19:44:00 | 2017-01-17 19:44:00 |
| 42 | 2017-02-01 16:00:00 | 41 | 1 | 250 | 0 | | <null> | 2017-01-30 12:40:21 | 2017-01-30 12:40:21 |
| 62 | 2017-03-03 11:00:00 | 48 | 1 | 60 | <null> | Biología Molecular 2 | <null> | 2017-01-31 20:59:19 | 2017-01-31 20:59:19 |
| 88 | 2017-03-03 12:30:00 | 49 | 1 | 70 | <null> | Citogenética 2 | <null> | 2017-02-01 04:49:44 | 2017-02-01 04:49:44 |
| 99 | 2017-02-17 17:00:00 | 28 | 1 | 120 | <null> | Examen de 130 reactivos | <null> | 2017-02-16 16:01:08 | 2017-02-16 16:01:08 |
| 109 | 2017-02-23 09:00:00 | 34 | 1 | 180 | <null> | Examen de 65 casos Neuro fisiología | <null> | 2017-02-21 18:37:57 | 2017-02-21 18:37:57 |
| 112 | 2017-02-25 09:00:00 | 47 | 1 | 180 | <null> | Examen de 61 casos en Tlatelolco | <null> | 2017-02-21 22:03:19 | 2017-02-21 22:03:19 |
| 121 | 2017-02-25 10:00:00 | 41 | 1 | 240 | <null> | Examen de 71 casos en Universisad Anuahuac | <null> | 2017-02-21 22:31:37 | 2017-02-21 22:31:37 |
| 123 | 2017-02-25 09:00:00 | 18 | 1 | 180 | <null> | Examen de 60 casos hematología adultos | <null> | 2017-02-22 13:50:20 | 2017-02-22 13:50:20 |
答案 0 :(得分：1)
我的回答是假设您只想包含实际参加考试的用户结果（至少回答了1个问题）。
由于我不知道您是否有任何表格显示谁订阅了哪些考试（如果不这样做，您应该这样做），我必须通过获取所有不同的考试ID来创建参加考试的用户列表 - 用户ID将子查询中的对作为派生表。
此外，考试和问题表之间存在脱节 - 可能有一个连接两个表的插槽表。由于这种脱节，我被迫使用派生表中的答案表来加入考试和问题。但是，这意味着在同一考试的不同位置提出的问题无法相互区分。此外，这意味着如果所有用户都跳过相同的问题，那么它就不会显示在结果中。
我inner join问题以及派生表上的distractors表中的正确选项，并在此处加入用户的答案。我将在连接中使用括号来强制MySQL创建考试 - 用户 - 问题 - 首先正确回答结果集，然后进行左连接。
select t1.exam_id, t2.question_id, d.option, (d.option=a.answer) as correct, t1.user_id, a.answer
from
(
(select distinct exam_id, user_id from answers) t1
inner join
(select distinct exam_id, question_id from answers) t2 a on t1.exam_id=t2.exam_id
inner join questions q on t2.question_id=q.id
inner join distractors d on q.id=d.question_id and d.correct=1
)
left join answers a on t1.exam_id=a.exam_id and t1.user_id=a.user_id and q.id=a.question_id
答案 1 :(得分：0)
看起来你是在随意尝试一些事情而没有真正理解表格如何相互关联或你想要的数据。您需要系统地处理此问题，并了解数据的含义。不只是随意尝试加入。
我建议将其分解为步骤，然后逐步添加每条新信息并检查结果。如果遇到问题，这可以帮助您隔离信息开始的确切位置。如果您从一个考试和一个用户开始，并在删除这些条件之前先使用小数据集直接获取所有内容，这也会很有帮助。
首先，您需要知道哪些问题属于哪个考试以及正确答案是什么。因为你不需要彼此之间没有关系的问题和答案，所以这些很可能需要是内部联接。
然后，您需要为参加考试的用户添加联接。请注意，如果您要处理他们未回答的问题，则此加入需要考试而不是问题。由于您只对具有已回答问题的用户的考试感兴趣，因此这需要是内部联接。
然后，您添加用户对考试中问题的答案。现在您使用左连接，因为参加考试的用户将无法回答一些问题。
然后你可以将他们的答案与正确答案进行比较。
我无法弄清楚干扰器是什么，所以我还没有把它包括在内。不知何故，如果你需要它，你需要了解这与其余的意义有什么关系。一旦理解了含义，语法就会变得清晰。