请教下SELECT areaname FROM area WHERE areaid = ROUND(rand()*32)这句话为什么有时候会出现多条记录？？
mysql版本：5.7.23-log MySQL Community Server (GPL)
表结构：
CREATE TABLE area (
areaid int(11) NOT NULL,
areaname varchar(50) DEFAULT NULL,
parentId int(11) DEFAULT NULL,
PRIMARY KEY (areaid)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
数据：
INSERT INTO area VALUES (1, '北京', '4744');
INSERT INTO area VALUES (2, '上海', '4744');
INSERT INTO area VALUES (3, '天津', '4744');
INSERT INTO area VALUES (4, '重庆', '4744');
INSERT INTO area VALUES (5, '河北', '4744');
INSERT INTO area VALUES (6, '山西', '4744');
INSERT INTO area VALUES (7, '河南', '4744');
INSERT INTO area VALUES (8, '辽宁', '4744');
INSERT INTO area VALUES (9, '吉林', '4744');
INSERT INTO area VALUES (10, '黑龙江', '4744');
INSERT INTO area VALUES (11, '内蒙古', '4744');
INSERT INTO area VALUES (12, '江苏', '4744');
INSERT INTO area VALUES (13, '山东', '4744');
INSERT INTO area VALUES (14, '安徽', '4744');
INSERT INTO area VALUES (15, '浙江', '4744');
INSERT INTO area VALUES (16, '福建', '4744');
INSERT INTO area VALUES (17, '湖北', '4744');
INSERT INTO area VALUES (18, '湖南', '4744');
INSERT INTO area VALUES (19, '广东', '4744');
INSERT INTO area VALUES (20, '广西', '4744');
INSERT INTO area VALUES (21, '江西', '4744');
INSERT INTO area VALUES (22, '四川', '4744');
INSERT INTO area VALUES (23, '海南', '4744');
INSERT INTO area VALUES (24, '贵州', '4744');
INSERT INTO area VALUES (25, '云南', '4744');
INSERT INTO area VALUES (26, '西藏', '4744');
INSERT INTO area VALUES (27, '陕西', '4744');
INSERT INTO area VALUES (28, '甘肃', '4744');
INSERT INTO area VALUES (29, '青海', '4744');
INSERT INTO area VALUES (30, '宁夏', '4744');
INSERT INTO area VALUES (31, '新疆', '4744');
INSERT INTO area VALUES (32, '台湾', '4744');