MySQL - Tôi nên sử dụng Hash Algo nào cho việc này?

Có lẽ bạn có thể triển khai thuật toán levenshtein thành mysql dưới dạng một hàm được lưu trữ, dưới đây là một ví dụ, hy vọng nó sẽ giúp ích:

DELIMITER //
CREATE FUNCTION levenshtein( s1 VARCHAR(255), s2 VARCHAR(255) )
  RETURNS INT
  DETERMINISTIC
  BEGIN
    DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
    DECLARE s1_char CHAR;
    -- max strlen=255
    DECLARE cv0, cv1 VARBINARY(256);
    SET s1_len = CHAR_LENGTH(s1), s2_len = CHAR_LENGTH(s2), cv1 = 0x00, j = 1, i = 1, c = 0;
    IF s1 = s2 THEN
      RETURN 0;
    ELSEIF s1_len = 0 THEN
      RETURN s2_len;
    ELSEIF s2_len = 0 THEN
      RETURN s1_len;
    ELSE
      WHILE j <= s2_len DO
        SET cv1 = CONCAT(cv1, UNHEX(HEX(j))), j = j + 1;
      END WHILE;
      WHILE i <= s1_len DO
        SET s1_char = SUBSTRING(s1, i, 1), c = i, cv0 = UNHEX(HEX(i)), j = 1;
        WHILE j <= s2_len DO
          SET c = c + 1;
          IF s1_char = SUBSTRING(s2, j, 1) THEN 
            SET cost = 0; ELSE SET cost = 1;
          END IF;
          SET c_temp = CONV(HEX(SUBSTRING(cv1, j, 1)), 16, 10) + cost;
          IF c > c_temp THEN SET c = c_temp; END IF;
            SET c_temp = CONV(HEX(SUBSTRING(cv1, j+1, 1)), 16, 10) + 1;
            IF c > c_temp THEN 
              SET c = c_temp; 
            END IF;
            SET cv0 = CONCAT(cv0, UNHEX(HEX(c))), j = j + 1;
        END WHILE;
        SET cv1 = cv0, i = i + 1;
      END WHILE;
    END IF;
    RETURN c;
  END; 

Nguồn http://www.artfulsoftware.com/infotree/queries.php#552 (Đã sửa bằng cách thêm DELIMITER // )

Tập lệnh mẫu thử nghiệm

<?php
//I inserted these test words into a test database
$words = 'back, lack, pack, rack, sack, tack, yak, black, knack, quack, slack, smack, snack, stack, track, whack, attack,bale, fail, hail, mail, male, nail, pail, tale, rail, sail, stale, scale, snail, whale, detail, email,air, bare, care, chair, dare, fair, hair, pair, rare, wear, chair, flare, stare, scare, share, spare, square, there, where, aware, beware, compare, declare, despair, prepare, repair, unfair,ache, bake, fake, lake, make, rake, take, brake, break, flake, quake, snake, steak, awake, mistake,all, ball, call, doll, hall, fall, tall, crawl, small, baseball, football,an, can, fan, man, pan, ran, tan, van, plan, scan, span, began,and, band, hand, land, sand, bland, command, demand, expand, stand, understand,cap, gap, map, nap, tap, zap, chap, clap, flap, slap, snap, strap, trap, wrap,are, bar, car, far, jar, tar, star, scar, afar, guitar,at, bat, fat, mat, pat, rat, sat, flat, that, splat, combat,ate, date, fate, mate, late, gate, rate, wait, crate, great, plate, skate, slate, state, straight, trait, weight, create,bed, dead, fed, head, led, read, red, said, bread, fled, spread, thread, tread, instead,bell, fell, sell, well, yell, shell, smell, spell, farewell, hotel, motel,den, hen, men, pen, ten, glen, then, when, wren, again,bet, get, jet, let, met, pet, set, vet, wet, yet, threat, barrette, reset, upset,bin, chin, in, pin, tin, grin, thin, twin, skin, begin, within,king, ring, sing, wing, zing, bring, cling, fling, sling, spring, sting, string, swing, thing,bit, fit, hit, it, kit, lit, pit, sit, flit, knit, quit, skit, slit, spit, split, admit, commit, permit,bite, kite, bright, fight, fright, knight, night, might, right, tight, white, write, delight, tonight,go, hoe, low, mow, row, sew, toe, blow, crow, dough, flow, know, glow, grow, know, show, slow, snow, stow, though, throw, ago, although, below,cot, dot, got, hot, lot, not, pot, rot, tot, bought, fought, knot, taught, shot, spot, squat, forgot,crowned, found, ground, hound, mound, pound, round, sound, wound, around, surround,bows, hose, nose, rose, toes, blows, flows, froze, grows, those,cub, rub, sub, tub, club, stub, scrub, shrub ,bun, fun, gun, one, run, son, sun, ton, won, done, none, begun, outdone, undone';

//A Class for db connection
Class DB{
    private $db;

    function __construct($host,$dbname,$user,$pass){
        $this->dbhost = $host;
        $this->dbname = $dbname;
        $this->dbuser = $user;
        $this->dbpass = $pass;
    }

    private function connect(){
        if (!$this->db instanceof PDO){
            $this->db = new PDO('mysql:dbname='.$this->dbname.';host='.$this->dbhost, $this->dbuser, $this->dbpass);
            $this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        }
    }

    //A Model method for the levenshtein_query.
    public function levenshtein_query($word,$dist){
        $this->connect();
        $sql = "SELECT `word` FROM `words` WHERE levenshtein( :word ,`word` ) BETWEEN 0 AND $dist";
        $statement = $this->db->prepare($sql);
        $statement->bindParam(':word', $word, PDO::PARAM_STR);
        $statement->execute();
        return $statement->fetchAll(PDO::FETCH_ASSOC);
    }
}

//ini the model class
$model = new DB('localhost','test_db','root','');

//The Word posted
$word = 'eet';
$result = $model->levenshtein_query($word,1);

print_r($result);
/*
//The Result
Array
(
    [0] => Array
        (
            [word] => bet
        )

    [1] => Array
        (
            [word] => get
        )

    [2] => Array
        (
            [word] => jet
        )

    [3] => Array
        (
            [word] => let
        )

    [4] => Array
        (
            [word] => met
        )

    [5] => Array
        (
            [word] => pet
        )

    [6] => Array
        (
            [word] => set
        )

    [7] => Array
        (
            [word] => vet
        )

    [8] => Array
        (
            [word] => wet
        )

    [9] => Array
        (
            [word] => yet
        )

    [10] => Array
        (
            [word] => meet
        )

)

*/

Có lẽ nó quan tâm ...