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drop procedure if exists 获取姓名字符串;
DELIMITER $$
CREATE PROCEDURE 获取姓名字符串()
BEGIN
    DECLARE 姓名长度 INT;
    DECLARE i INT;
    DECLARE 单个字符 CHAR(1);
    DECLARE 学生姓名 VARCHAR(255);
    DECLARE 完成 BOOL DEFAULT FALSE;

    DECLARE cur CURSOR FOR SELECT 姓名 FROM md;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET 完成 = TRUE;

    TRUNCATE TABLE zi;

    OPEN cur;

    fetch_loop: LOOP
        FETCH cur INTO 学生姓名;
        IF 完成 THEN
            LEAVE fetch_loop;
        END IF;

        SET 姓名长度 = CHAR_LENGTH(学生姓名);
        SET i = 1;

        char_loop: LOOP
            IF i > 姓名长度 THEN
                LEAVE char_loop;
            END IF;

            SET 单个字符 = SUBSTRING(学生姓名, i, 1);

            INSERT IGNORE INTO zi (字, 字数) VALUES (LOWER(单个字符), 1) ON DUPLICATE KEY UPDATE 字数 = 字数 + 1;

            SET i = i + 1;
        END LOOP char_loop;
    END LOOP fetch_loop;

    CLOSE cur;

    SELECT GROUP_CONCAT(DISTINCT 字 ORDER BY 字 SEPARATOR '') AS 字符串 FROM zi;

    SELECT COUNT(DISTINCT 字) INTO @n2 FROM zi;
    SELECT @n2 AS 总唯一字符数;
END $$
DELIMITER ;


call 获取姓名字符串();