mysql - LEFT JOIN 不会响应

Question

现在已经为此工作了几个小时。尝试在 vb.net 中组合多个表(大约 42 个表)作为数据集，但查询不会响应并且超时。

SELECT        accounts.`1st_test` AS acc1, accounts.`2nd_test` AS acc2, accounts.exam AS accExam, accounts.result_total AS accTotal, accounts.result_grade AS accGrade, agricultural_science.`1st_test` AS agric1, 
                     agricultural_science.`2nd_test` AS agric2, agricultural_science.exam AS agricExam3, agricultural_science.result_total AS agricTotal, agricultural_science.result_grade AS agricGrade, 
                     animal_husbandry.`1st_test` AS ani1, animal_husbandry.`2nd_test` AS ani2, animal_husbandry.exam AS aniExam, animal_husbandry.result_total AS aniTotal, animal_husbandry.result_grade AS aniGrade, 
                     basic_science.`1st_test` AS basicsci1, basic_science.`2nd_test` AS basicsci2, basic_science.exam AS basicsciExam, basic_science.result_total AS basicsciTotal, basic_science.result_grade AS basicsciGrade, 
                     basic_science_technology.`1st_test` AS basicscitech1, basic_science_technology.`2nd_test` AS basicscitech2, basic_science_technology.exam AS basicscitechExam, 
                     basic_science_technology.result_total AS basicscitechTotal, basic_science_technology.result_grade AS basicscitechGrade, basic_technology.`1st_test` AS basictech1, basic_technology.`2nd_test` AS basictech2,
                      basic_technology.exam AS basictechExam, basic_technology.result_total AS basictechTotal, basic_technology.result_grade AS basictechGrade, biology.result_grade AS bioGrade, biology.result_total AS bioTotal,
                      biology.exam AS bioExam, biology.`2nd_test` AS bio2, biology.`1st_test` AS bio1, business_studies.result_grade AS busGrade, business_studies.result_total AS busTotal, business_studies.exam AS busExam, 
                     business_studies.`2nd_test` AS bus2, business_studies.`1st_test` AS bus1, chemistry.result_grade AS chemGrade, chemistry.result_total AS chemTotal, chemistry.exam AS chemExam, 
                     chemistry.`2nd_test` AS chem2, chemistry.`1st_test` AS chem1, commerce.result_total AS commTotal, commerce.exam AS commExam, commerce.`2nd_test` AS comm2, commerce.`1st_test` AS comm1, 
                     commerce.result_grade AS commGrade, civic_education.result_grade AS civicGrade, civic_education.result_total AS civicTotal, civic_education.exam AS civicExam, civic_education.`2nd_test` AS civic2, 
                     civic_education.`1st_test` AS civic1, christian_religious_studies.result_grade AS crsGrade, christian_religious_studies.result_total AS crsTotal, christian_religious_studies.exam AS crsExam, 
                     christian_religious_studies.`2nd_test` AS crs2, christian_religious_studies.`1st_test` AS crs1, current_affairs.result_grade AS affairsGrade, current_affairs.result_total AS affairsTotal, 
                     current_affairs.exam AS affairsExam, current_affairs.`2nd_test` AS affairs2, current_affairs.`1st_test` AS affairs1, cultural_creative_art.result_grade AS ccaGrade, cultural_creative_art.result_total AS ccaTotal, 
                     cultural_creative_art.exam AS ccaExam, cultural_creative_art.`2nd_test` AS cca2, cultural_creative_art.`1st_test` AS cca1, computer_science.result_grade AS cscGrade, computer_science.result_total AS cscTotal, 
                     computer_science.exam AS cscExam, computer_science.`2nd_test` AS csc2, computer_science.`1st_test` AS csc1, english_language.`1st_test` AS eng1, english_language.`2nd_test` AS eng2, 
                     english_language.exam AS engExam, english_language.result_total AS engTotal, english_language.result_grade AS engGrade, elementary_science.result_grade AS elementarysciGrade, 
                     elementary_science.result_total AS elementarysciTotal, elementary_science.exam AS elementarysciExam, elementary_science.`2nd_test` AS elementarysci2, elementary_science.`1st_test` AS elementarysci1, 
                     economics.`1st_test` AS econs1, economics.`2nd_test` AS econs2, economics.exam AS econsExam, economics.result_total AS econsTotal, economics.result_grade AS econsGrade, french.`1st_test` AS french1, 
                     french.`2nd_test` AS french2, french.exam AS frenchExam, french.result_total AS frenchTotal, french.result_grade AS frenchGrade, food_nutrition.result_grade AS foodGrade, food_nutrition.result_total AS foodTotal, 
                     food_nutrition.exam AS foodExam, food_nutrition.`2nd_test` AS food2, food_nutrition.`1st_test` AS food1, fine_art.result_grade AS fineArtGrade, fine_art.result_total AS fineArtTotal, fine_art.exam AS fineArtExam, 
                     fine_art.`2nd_test` AS fineArt2, fine_art.`1st_test` AS fineArt1, geography.result_grade AS geoGrade, geography.result_total AS geoTotal, geography.exam AS geoExam, geography.`2nd_test` AS geo2, 
                     geography.`1st_test` AS geo1, general_paper.result_grade AS gpGrade, general_paper.result_total AS gpTotal, general_paper.exam AS gpExam, general_paper.`2nd_test` AS gp2, general_paper.`1st_test` AS gp1,
                      further_mathematics.result_grade AS fmathsGrade, further_mathematics.result_total AS fmathsTotal, further_mathematics.exam AS fmathsExam, further_mathematics.`2nd_test` AS fmaths2, 
                     further_mathematics.`1st_test` AS fmaths1, history.result_grade AS hisGrade, history.result_total AS hisTotal, history.exam AS hisExam, history.`2nd_test` AS his2, history.`1st_test` AS his1, 
                     health_education.result_grade AS healthGrade, health_education.result_total AS healthTotal, health_education.exam AS healthExam, health_education.`2nd_test` AS health2, 
                     health_education.`1st_test` AS health1, government.result_grade AS govtGrade, government.result_total AS govtTotal, government.exam AS govtExam, government.`2nd_test` AS govt2, 
                     government.`1st_test` AS govt1, home_economics.`1st_test` AS homeecons1, home_economics.`2nd_test` AS homeecons2, home_economics.exam AS homeeconsExam, 
                     home_economics.result_total AS homeeconsTotal, home_economics.result_grade AS homeeconsGrade, islamic_studies.`1st_test` AS islamic1, islamic_studies.`2nd_test` AS islamic2, 
                     islamic_studies.exam AS islamicExam, islamic_studies.result_total AS islamicTotal, islamic_studies.result_grade AS islamicGrade, lit_in_english.result_total AS litTotal, lit_in_english.result_grade AS litGrade, 
                     lit_in_english.exam AS litExam, lit_in_english.`2nd_test` AS lit2, lit_in_english.`1st_test` AS lit1, local_craft.result_grade AS localCraftGrade, local_craft.result_total AS localCraftTotal, 
                     local_craft.exam AS localCraftExam, local_craft.`2nd_test` AS localCraft2, local_craft.`1st_test` AS localCraft1, mathematics.`1st_test` AS maths1, mathematics.`2nd_test` AS maths2, 
                     mathematics.exam AS mathsExam, mathematics.result_total AS mathsTotal, mathematics.result_grade AS mathsGrade, local_language.result_grade AS locallangGrade, 
                     local_language.result_total AS locallangTotal, local_language.exam AS locallangExam, local_language.`2nd_test` AS locallang2, local_language.`1st_test` AS locallang1, music.`1st_test` AS music1, 
                     music.`2nd_test` AS music2, music.exam AS musicExam, music.result_total AS musicTotal, music.result_grade AS musicGrade, quantitative_reasoning.`1st_test` AS qr1, quantitative_reasoning.`2nd_test` AS qr2, 
                     quantitative_reasoning.exam AS qrExam, quantitative_reasoning.result_total AS qrTotal, quantitative_reasoning.result_grade AS qrGrade, physics.result_grade AS phyGrade, physics.result_total AS phyTotal, 
                     physics.exam AS phyExam, physics.`2nd_test` AS phy2, physics.`1st_test` AS phy1, physical_health_education.`1st_test` AS phe1, physical_health_education.`2nd_test` AS phe2, 
                     physical_health_education.exam AS pheExam, physical_health_education.result_total AS pheTotal, physical_health_education.result_grade AS pheGrade, social_studies.`1st_test` AS social1, 
                     social_studies.`2nd_test` AS social2, social_studies.exam AS socialExam, social_studies.result_total AS socialTotal, social_studies.result_grade AS socialGrade, verbal_reasoning.`1st_test` AS vr1, 
                     verbal_reasoning.`2nd_test` AS vr2, verbal_reasoning.exam AS vrExam, verbal_reasoning.result_total AS vrTotal, verbal_reasoning.result_grade AS vrGrade, technical_drawing.result_grade AS TechDrawGrade, 
                     technical_drawing.result_total AS TechDrawTotal, technical_drawing.exam AS TechDrawExam, technical_drawing.`2nd_test` AS TechDraw2, technical_drawing.`1st_test` AS TechDraw1, 
                     result_summary.student_id, result_summary.result_term, result_summary.result_session, result_summary.result_level, result_summary.result_class
FROM            ((((((((((((((((((((((((((((((((((((((((result_summary LEFT JOIN
                         agricultural_science ON result_summary.student_id = agricultural_science.student_id) LEFT JOIN
                         animal_husbandry ON result_summary.student_id = animal_husbandry.student_id) LEFT JOIN
                         basic_science ON result_summary.student_id = basic_science.student_id) LEFT JOIN
                         basic_science_technology ON result_summary.student_id = basic_science_technology.student_id) LEFT JOIN
                         basic_technology ON result_summary.student_id = basic_technology.student_id) LEFT JOIN
                         biology ON result_summary.student_id = biology.student_id) LEFT JOIN
                         business_studies ON result_summary.student_id = business_studies.student_id) LEFT JOIN
                         chemistry ON result_summary.student_id = chemistry.student_id) LEFT JOIN
                         christian_religious_studies ON result_summary.student_id = christian_religious_studies.student_id) LEFT JOIN
                         civic_education ON result_summary.student_id = civic_education.student_id) LEFT JOIN
                         commerce ON result_summary.student_id = commerce.student_id) LEFT JOIN
                         computer_science ON result_summary.student_id = computer_science.student_id) LEFT JOIN
                         cultural_creative_art ON result_summary.student_id = cultural_creative_art.student_id) LEFT JOIN
                         current_affairs ON result_summary.student_id = current_affairs.student_id) LEFT JOIN
                         economics ON result_summary.student_id = economics.student_id) LEFT JOIN
                         elementary_science ON result_summary.student_id = elementary_science.student_id) LEFT JOIN
                         english_language ON result_summary.student_id = english_language.student_id) LEFT JOIN
                         fine_art ON result_summary.student_id = fine_art.student_id) LEFT JOIN
                         food_nutrition ON result_summary.student_id = food_nutrition.student_id) LEFT JOIN
                         french ON result_summary.student_id = french.student_id) LEFT JOIN
                         further_mathematics ON result_summary.student_id = further_mathematics.student_id) LEFT JOIN
                         general_paper ON result_summary.student_id = general_paper.student_id) LEFT JOIN
                         geography ON result_summary.student_id = geography.student_id) LEFT JOIN
                         government ON result_summary.student_id = government.student_id) LEFT JOIN
                         health_education ON result_summary.student_id = health_education.student_id) LEFT JOIN
                         history ON result_summary.student_id = history.student_id) LEFT JOIN
                         home_economics ON result_summary.student_id = home_economics.student_id) LEFT JOIN
                         islamic_studies ON result_summary.student_id = islamic_studies.student_id) LEFT JOIN
                         lit_in_english ON result_summary.student_id = lit_in_english.student_id) LEFT JOIN
                         local_craft ON result_summary.student_id = local_craft.student_id) LEFT JOIN
                         local_language ON result_summary.student_id = local_language.student_id) LEFT JOIN
                         mathematics ON result_summary.student_id = mathematics.student_id) LEFT JOIN
                         music ON result_summary.student_id = music.student_id) LEFT JOIN
                         physical_health_education ON result_summary.student_id = physical_health_education.student_id) LEFT JOIN
                         physics ON result_summary.student_id = physics.student_id) LEFT JOIN
                         quantitative_reasoning ON result_summary.student_id = quantitative_reasoning.student_id) LEFT JOIN
                         accounts ON result_summary.student_id = accounts.student_id) LEFT JOIN
                         social_studies ON result_summary.student_id = social_studies.student_id) LEFT JOIN
                         technical_drawing ON result_summary.student_id = technical_drawing.student_id) LEFT JOIN
                         verbal_reasoning ON result_summary.student_id = verbal_reasoning.student_id) WHERE result_summary.student_id = '334'

该记录存在于某些表中，而不是全部表中。请问我需要帮助还是有其他方法？

Answer 1

这是一个非常复杂的查询，肯定需要一些时间。 ADO.NET 命令对象的默认超时时间为 30 秒，因此如果超过该时间，查询将超时。如果您需要更长的时间，请将 MySqlCommand 的 CommndTimeout 属性设置为适当的值。