查詢Mysql上的相關表格

我有2個表與一對多索引相關。這是我第一次在這種情況下，我試圖找出一個很好的智能查詢來檢索數據。查詢Mysql上的相關表格

表名稱：問題

結構：

id poll_id question

表名稱：回答

結構：

id question_id answer

question_id從表anwsers是ID對問題表forehing關鍵。

我需要檢索所有問題（以及相應的答案選項）給出poll_id。到目前爲止，我有這個查詢：

'SELECT * FROM polls_questions pq, polls_answers WHERE `poll_id` = ' . $pid

但是返回的數組是可怕的低效率，惠特數據重複多次。

對於4個問題的投票我得到35個元素;

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 
     ) 

)

我可以解決這個只用兩個查詢，一個問題，一個是答案，這會給我兩個數組，但這樣做沒有一點對錶之間的關係。我如何查詢數據庫並以最佳方式檢索問題和答案？

來源

2013-02-06 DomingoSL

你不能在任何列，所以你得到一個笛卡爾結果集連接表：

'SELECT * 
FROM polls_questions pq 
INNER JOIN polls_answers pa 
    on pq.id = pa.question_id 
WHERE `poll_id` = ' . $pid

您應該使用JOIN語法，在那裏你連接表上的問題編號。這是確保你只會回答與答案的問題。否則，您將回答每個問題與每個答案。

我在兩個表之間使用了一個INNER JOIN，它將返回兩個表之間的匹配行。如果您想回答所有問題，即使答案中沒有匹配的行，那麼您也需要一個LEFT JOIN。

如果您需要幫助瞭解連接語法，這裏是一個偉大的visual explanation of joins

來源

2013-02-06 16:44:34 Taryn

'SELECT * 
FROM polls_questions pq, polls_answers 
WHERE `poll_id` = ' . $pid . ' AND pq.id = polls_answers.question_id'

來源

2013-02-06 16:45:20 75inchpianist

查詢Mysql上的相關表格

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