SQL multiple select ... where id in and DISTINCT

Question

我在MySQL數據庫的一個表中運行一個查詢，其中包含多個「where id in」子句。我在每個查詢中加入了DISTINCT，試圖減少結果的數量。仍然鎖定我的MySQL表。任何我不知道的故障，或者我應該嘗試擺脫一些DISTICT？只有第一個DISTINCT是必要的。

SELECT DISTINCT id, name 
    FROM TP_Test_Info 
    WHERE id IN (SELECT DISTINCT test_id 
       FROM TP_Test_Sections 
       WHERE id IN (SELECT DISTINCT section_id 
          FROM TP_Test_Questions 
          WHERE id IN (SELECT DISTINCT question_id 
              FROM TP_Student_Answers 
              WHERE student_id = 751))) 

最後一個表TP_Student_Answers有大約32,000個條目。其餘的要小得多。

我意識到我應該在大表中索引一些行。隔開它。任何其他問題突出？

Answer 1

您應該使用joins，並考慮創建索引至少在foreign keys

請嘗試以下

SELECT DISTINCT TP_Test_Info.id, TP_Test_Info.name 
FROM TP_Test_Info 
JOIN TP_Test_Sections 
    ON TP_Test_Sections.test_id = TP_Test_Info.id 
JOIN TP_Test_Questions 
    ON TP_Test_Questions.section_id = TP_Test_Sections.id 
JOIN TP_Student_Answers 
    ON TP_Student_Answers.question_id = TP_Test_Questions.id 
WHERE TP_Student_Answers.student_id = 751