Função para encodar strings em MySQL com o algoritmo base64 http://www.programabrasil.org/mysql-base64-encode-sem-tabela-de-conversao/

MySQL base64_encode

DELIMITER $$

USE `YOUR DATABASE`$$

DROP FUNCTION IF EXISTS `BASE64_ENCODE`$$

CREATE DEFINER=`YOUR DATABASE`@`%` FUNCTION `BASE64_ENCODE`(input BLOB) RETURNS BLOB
    DETERMINISTIC
    SQL SECURITY INVOKER
BEGIN
    DECLARE ret BLOB DEFAULT '';
    DECLARE done TINYINT DEFAULT 0;
    IF input IS NULL THEN
        RETURN NULL;
    END IF;
each_block:
    WHILE NOT done DO BEGIN
        DECLARE accum_value BIGINT UNSIGNED DEFAULT 0;
        DECLARE in_count TINYINT DEFAULT 0;
        DECLARE out_count TINYINT;
each_input_char:
        WHILE in_count < 3 DO BEGIN
            DECLARE first_char BLOB(1);

            IF LENGTH(input) = 0 THEN
                SET done = 1;
                SET accum_value = accum_value << (8 * (3 - in_count));
                LEAVE each_input_char;
            END IF;

            SET first_char = SUBSTRING(input,1,1);
            SET input = SUBSTRING(input,2);

            SET accum_value = (accum_value << 8) + ASCII(first_char);
            SET in_count = in_count + 1;
        END; END WHILE;

        -- We've now accumulated 24 bits; deaccumulate into base64 characters
        -- We have to work from the left, so use the third byte position and shift left
        CASE
            WHEN in_count = 3 THEN SET out_count = 4;
            WHEN in_count = 2 THEN SET out_count = 3;
            WHEN in_count = 1 THEN SET out_count = 2;
            ELSE RETURN ret;
        END CASE;

        WHILE out_count > 0 DO BEGIN
            BEGIN
                DECLARE out_char CHAR(1);
                DECLARE base64_getval CURSOR FOR SELECT c FROM core_base64_data WHERE val = (accum_value >> 18);
                OPEN base64_getval;
                FETCH base64_getval INTO out_char;
                CLOSE base64_getval;
                SET ret = CONCAT(ret,out_char);
                SET out_count = out_count - 1;
                SET accum_value = accum_value << 6 & 0xffffff;
            END;
        END; END WHILE;
        CASE
            WHEN in_count = 2 THEN SET ret = CONCAT(ret,'=');
            WHEN in_count = 1 THEN SET ret = CONCAT(ret,'==');
            ELSE BEGIN END;
        END CASE;

    END; END WHILE;
    RETURN ret;
END$$

DELIMITER ;