在mysql中迭代字符串中的字符

Question

首先,我有一个非常具体的问题,但也许我的问题的另一种方法(第二部分)也可以帮助我.

有没有办法通过mysql中的索引来解决字符串中的字符.(即PHP $ var [2]会给你第3个字符)？

显而易见的方法是SUBSTRING(var, 3,1 ),因为我的字符串长度为1024个字符,所以我认为这不是最快的解决方案.如代码示例所示,使用子字符串来检索字符串的尾部也没有获得性能差异.有没有办法迭代字符串？(转移第一个元素？)

CREATE FUNCTION hashDiff( hash1 TEXT(1024), hash2 TEXT(1024), threshold INT) 
RETURNS INT
DETERMINISTIC
BEGIN
    DECLARE diff, x, b1, b2 INT;
    SET diff =0;
    SET x = 0;
    WHILE (x<1024 AND diff<threshold)  DO
        SET b1 = ASCII(hash1); --uses first character only!!
        SET b2 = ASCII(hash2);
        SET hash1=SUBSTRING(hash1, 2 );
        SET hash2=SUBSTRING(hash2, 2 );
        SET diff=diff+ ((b1-b2)*(b1-b2));
        SET x=x+1;
    END WHILE;
    RETURN diff;
END 

如果您还没有从代码中读取它,我会尝试编写一个存储过程来计算哈希值之间的差异或距离.差异是字符方形距离(即hashDiff(AA,AC)=(65-65)²+(65-67)²=4)的总和.如果散列已经不同,则可以通过引入阈值来取消计算来实现第一次主要性能提升.但由于mysql不是我的"日常"语言,我在这一点上坚持寻找其他优化.为了完整性,两个样本哈希:

YAAAAAAYAAAYAAVAAQAARAOAAOAQASAQAMAKAKAJIAJAJIAHAHIAKJAIIAHHAHIIAIHGAGFFAGGFEAFEEEEAEDDDDDAEEEEDEEEFAFFFFFFEFFFEFFFFFGFEEFFEEEFFFJEFFEEEEEEELFFFFEEFJEEEEDIEEEEEIEEEEHEEEJEEFKFEFKGGFNHGOIIJTJKYONYNMTGHNHHQISJJQIKWLXJJSMYRQWJOGKDDFCCBBAAAAAAAAAAAAAAAAAAAAAAAYAAAAAAYAAAYAAWAARAASASAAQARAUAYAYATAOALKAJAJIAIAHHAHGAGFAFFAEFFAEFFAFFFAEEFFAFEEEDADEDDDDADDDCDDDDDAEEEFEEEEDDDEEEDEDDEEEFEFFGGFMFHGFFFGFFFLGHGGHGGNHHGGGOHGHGHMGGFGMFFFMFGFLFFFMGFFMGGMGGGNGGMGGLGGLGGMGGLEIEEHDCGCGCDGDGDCGDFCECCECECECECFCECFCFCFCFCFCGCJGYCYAAAAAAYAAAYAAUAATAAUAUAAUARARAQAPAPASARRAPARQAPAQQAQQAQSAKMATKKAIIHAIHGAGGGGAGHHGGAGGFGFFAFFGEFFFFFAFFGFGGGFFFEEFGFFGGFGGHIJJLKLWLKJJIJJJKJRLJKLKKKUKLLKKUMMKJIQIIIISKJJWKLLXMLMYMLNYMMYMLLWJIQIINFGKFFKEEIDHEDHDDFCECCFDECCFCFDGCDGCGCGEGCDCECECFDFCGDGCIEKEOAYNFBREUXKPQMMQTKTMMNJLPPVYYYTOUOPOLLJKKJJJIJIMJJJLIJJLLJIIHHIHHHIGHIHIHJHHHJHHIHGHGHFGHGFFEFEEEFEFEFFGGHIHIHGHGHHIIIIHIIJMNLONKLKKKKKKKMLKKLONMKOOOMLOPONMNMKKLLKKLMNKLMMMNMOPPOORPORSSVRTSSRTRRTSSTTXSTQRPONOKKLKLJMKJJIJIIHHHIIIJHIJIJJIJIKJIMWMYYDAAAAAAAAAAA

AAAAAAAAAAABAABAACAACACAACADADAEADADADADDAEAEEAEAFEAEEAEFAFGAGGGAGGGAHHHAHIIIAIHIJHAIIHIHHAJIHIJIJKJAJJJIKJJJJKKJKJKKLKLKLLMMMNNMYOOOOOOPOONYOONONNPYNOOOPYOOPPPYNONNYMLLWLLKUJIISHIHOGGMFGFLFFMGGLFGLGFLFFKFKFFLEEKFLEFJFKFGNGNHLFHJFIEGDIEKGOIRFGBBAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABABACACDACADDACADDADDAEDAFEAEEFAFFFAFFGAFGGGAIGHHIAHIHHHHAHIHIIJJIIAIIIIJIJKJIIIIJJHIIHIIIIJIIIIRJJJJKJJJJLVKLLKLLKXLMMKMXMLLLMWMMMMYMNLYMNNYNNMYMMNYMLYLMLXKJRIHPHIMGGMFEJEJEEIEEHDGCDFCFDCFCECECCEBEBECFDGCFDNGLDBAAAAAAAAAAAAAAAAAAAAAABAAAAABAABABAACACACACACACACADDADAEEAFAFGAFGAHGAGGAGGHAGGIAIHJAJJJJAJKKKKAMLMNNNANOMMNNMMNAONMNOOOMOOPOMNOMMNPOOPPPPRQQYPPRPPPPPNOYLLMMMMLYLMLMLYLMLMMYLNNMYNLLWMLKXLLLUKIKQIIQGHHPFHNGFLFFLGFJEEJEIDDIDCHDFCDGCFCCFCECECCECFCGDGDHDHDIFIDEBBAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAABBBBBCBCCCCDCCCCCCCCDDDDEDEEEEFFDEGGHGHHHGHHHHHHIIJJJJJIJJJJJJIKJJKLKKMMNMMMMMMMNNNNNNLNNONPONNNOOOOPQQQRSSSSSSUTSTUUUVWVVXUYXWVXVXWYVYWYVYYUWVUTTSSPQPQOPOPONONOMONOOONNNMMNLJJKJIIJHHGGGFHFGFFFFEEEDDEEEEFGGIGJLRNEAAAAAAAAAAAAA

任何帮助或提示将不胜感激.

Answer 1

能够使用排序数组的唯一方法是使用临时表和游标/结果集。

问题是您仍然需要迭代字符串并使用子字符串将它们分开。据我所知，没有“自动换行”或“爆炸”功能来分割字符串。