Question

我正在尝试在mysql中创建搜索功能。为了使搜索结果更可靠，我需要逐字比较两个字符串。输入是2个字符串，输出是数字2个字符串匹配。在MySql中我做了如下。

CREATE DEFINER=`root`@`localhost` FUNCTION `CompareStrings`(str1 VARCHAR(255),str2 VARCHAR(255)) RETURNS double
BEGIN
DECLARE cur_position INT DEFAULT 1 ; 
DECLARE remainder TEXT;
DECLARE cur_string VARCHAR(50);
DECLARE delimiter_length TINYINT UNSIGNED;
DECLARE numberMatch INT;
DECLARE total INT;
DECLARE result DOUBLE DEFAULT 0;
DECLARE delim VARCHAR(10);
DECLARE string2 VARCHAR(255);
SET delim = ' ';

DROP TEMPORARY TABLE IF EXISTS SplitString1;
CREATE TEMPORARY TABLE SplitString1 (
    SplitString1ID INT NOT NULL PRIMARY KEY AUTO_INCREMENT ,
    val VARCHAR(50) NOT NULL
) ENGINE=MyISAM;
DROP TEMPORARY TABLE IF EXISTS SplitString2;
CREATE TEMPORARY TABLE SplitString2 (
    SplitString1ID INT NOT NULL PRIMARY KEY AUTO_INCREMENT ,
    val VARCHAR(50) NOT NULL
) ENGINE=MyISAM;

SET remainder = str1;
SET delimiter_length = CHAR_LENGTH(delim);

WHILE CHAR_LENGTH(remainder) > 0 AND cur_position > 0 DO
    SET cur_position = INSTR(remainder, delim);
    IF cur_position = 0 THEN
        SET cur_string = remainder;

    ELSE
        SET cur_string = LEFT(remainder, cur_position - 1);
    END IF;
    IF TRIM(cur_string) != '' THEN
        INSERT INTO SplitString1(val) VALUES (cur_string);
    END IF;
    SET remainder = SUBSTRING(remainder, cur_position + delimiter_length);
END WHILE;
SET remainder = str2;
SET cur_position = 1;
WHILE CHAR_LENGTH(remainder) > 0 AND cur_position > 0 DO
    SET cur_position = INSTR(remainder, delim);
    IF cur_position = 0 THEN
        SET cur_string = remainder;

    ELSE
        SET cur_string = LEFT(remainder, cur_position - 1);
    END IF;
    IF TRIM(cur_string) != '' THEN
        INSERT INTO SplitString2(val) VALUES (cur_string);
    END IF;
    SET remainder = SUBSTRING(remainder, cur_position + delimiter_length);
END WHILE;
SELECT count(*) INTO numberMatch 
FROM SplitString1 s1 JOIN SplitString2 s2 ON s1.val = s2.val;
RETURN result;
END

这个想法是创建两个临时表存储每个单词，然后比较这两个表。结果很好，但性能很糟糕。任何人都有更好的想法，请给我一个建议。非常感谢！

Answer 1

我认为这不会像所说的那样奏效。

逻辑是合理的，但您没有为result变量分配任何值。因此，此函数将始终返回0.替换：

RETURN result;

与

RETURN numberMatch;

同时替换：

CREATE DEFINER=`root`@`localhost` FUNCTION `CompareStrings`(str1 VARCHAR(255),str2 VARCHAR(255)) RETURNS double

与

CREATE DEFINER=`root`@`localhost` FUNCTION `CompareStrings`(str1 VARCHAR(255),str2 VARCHAR(255)) RETURNS double READS SQL DATA

就效率而言，它看起来非常有效。当你说'表现糟糕'时 - 什么构成'糟糕'？你有任何基准数字，例如x个电话需要y millis？

用词比较mysql中的String函数

1 个答案: