我有两个与一对多索引相关的表。这是我第一次在这种情况下尝试找出一个很好的智能查询来检索数据。
表名： 问题
结构：
id poll_id question
表名： 答案
结构：
id question_id answer
question_id 是问题表中 id 的forehing键。
我需要在 poll_id 的情况下检索所有问题（以及相应的答案选项）。到目前为止，我有这个问题：
'SELECT * FROM polls_questions pq, polls_answers WHERE `poll_id` = ' . $pid
但是返回的数组效率很低，怀特数据重复了很多次。
对于4个问题的投票，我得到35个元素;
Array
(
[0] => Array
(
[id] => 1
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 1
[answer] => Risposta 1 domanda 1
)
[1] => Array
(
[id] => 1
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 1
[answer] => Risposta 1 domanda 1
)
[2] => Array
(
[id] => 1
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 1
[answer] => Risposta 1 domanda 1
)
[3] => Array
(
[id] => 1
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 1
[answer] => Risposta 1 domanda 1
)
[4] => Array
(
[id] => 2
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 1
[answer] => Risposta 2 domanda 1 (F: Domanda 3)
)
[5] => Array
(
[id] => 2
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 1
[answer] => Risposta 2 domanda 1 (F: Domanda 3)
)
[6] => Array
(
[id] => 2
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 1
[answer] => Risposta 2 domanda 1 (F: Domanda 3)
)
[7] => Array
(
[id] => 2
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 1
[answer] => Risposta 2 domanda 1 (F: Domanda 3)
)
[8] => Array
(
[id] => 3
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 2
[answer] => Risposta 1 domanda 2
)
[9] => Array
(
[id] => 3
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 2
[answer] => Risposta 1 domanda 2
)
[10] => Array
(
[id] => 3
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 2
[answer] => Risposta 1 domanda 2
)
[11] => Array
(
[id] => 3
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 2
[answer] => Risposta 1 domanda 2
)
[12] => Array
(
[id] => 4
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 2
[answer] => Risposta 2 domanda 2
)
[13] => Array
(
[id] => 4
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 2
[answer] => Risposta 2 domanda 2
)
[14] => Array
(
[id] => 4
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 2
[answer] => Risposta 2 domanda 2
)
[15] => Array
(
[id] => 4
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 2
[answer] => Risposta 2 domanda 2
)
[16] => Array
(
[id] => 5
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 3
[answer] => Risposta 1 domanda 3
)
[17] => Array
(
[id] => 5
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 3
[answer] => Risposta 1 domanda 3
)
[18] => Array
(
[id] => 5
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 3
[answer] => Risposta 1 domanda 3
)
[19] => Array
(
[id] => 5
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 3
[answer] => Risposta 1 domanda 3
)
[20] => Array
(
[id] => 6
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 3
[answer] => Risposta 2 domanda 3 (F: END POLL)
)
[21] => Array
(
[id] => 6
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 3
[answer] => Risposta 2 domanda 3 (F: END POLL)
)
[22] => Array
(
[id] => 6
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 3
[answer] => Risposta 2 domanda 3 (F: END POLL)
)
[23] => Array
(
[id] => 6
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 3
[answer] => Risposta 2 domanda 3 (F: END POLL)
)
[24] => Array
(
[id] => 7
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 4
[answer] => Risposta 1 domanda 4
)
[25] => Array
(
[id] => 7
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 4
[answer] => Risposta 1 domanda 4
)
[26] => Array
(
[id] => 7
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 4
[answer] => Risposta 1 domanda 4
)
[27] => Array
(
[id] => 7
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 4
[answer] => Risposta 1 domanda 4
)
[28] => Array
(
[id] => 8
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 4
[answer] => Risposta 2 domanda 4
)
[29] => Array
(
[id] => 8
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 4
[answer] => Risposta 2 domanda 4
)
[30] => Array
(
[id] => 8
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 4
[answer] => Risposta 2 domanda 4
)
[31] => Array
(
[id] => 8
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 4
[answer] => Risposta 2 domanda 4
)
[32] => Array
(
[id] => 9
[poll_id] => 1
[question] => Domanda 1
[atype] => 0
[question_id] => 4
[answer] => Risposta 3 domanda 4
)
[33] => Array
(
[id] => 9
[poll_id] => 1
[question] => Domanda 2
[atype] => 0
[question_id] => 4
[answer] => Risposta 3 domanda 4
)
[34] => Array
(
[id] => 9
[poll_id] => 1
[question] => Domanda 3
[atype] => 0
[question_id] => 4
[answer] => Risposta 3 domanda 4
)
[35] => Array
(
[id] => 9
[poll_id] => 1
[question] => Domanda 4
[atype] => 0
[question_id] => 4
[answer] => Risposta 3 domanda 4
)
)
我可以使用两个查询解决这个问题，一个用于问题，另一个用于答案，这将给我两个数组，但这样做就没有表格之间的关系。如何查询数据库并以最佳方式检索问题和答案？
答案 0 :(得分：0)
您没有加入任何列上的表格，因此您获得了一个笛卡尔结果集：
'SELECT *
FROM polls_questions pq
INNER JOIN polls_answers pa
on pq.id = pa.question_id
WHERE `poll_id` = ' . $pid
您应该使用JOIN语法加入问题ID的表格。这样可以确保您只返回带有答案的问题。否则，每个答案都会返回每个问题。
我在两个表之间使用INNER JOIN，这将返回两个表之间的匹配行。如果您想回答所有问题，即使答案中没有匹配的行，那么您需要LEFT JOIN。
如果您需要帮助了解联接语法，这里有一个很棒的visual explanation of joins
答案 1 :(得分：0)
'SELECT *
FROM polls_questions pq, polls_answers
WHERE `poll_id` = ' . $pid . ' AND pq.id = polls_answers.question_id'