mysql> SELECT goods_price FROM tdb_goods WHERE goods_cate='超極本';
Empty set (0.00 sec)

mysql> SELECT goods_price FROM tdb_goods WHERE goods_cate='筆記本';
+-------------+
| goods_price |
+-------------+
|??? 3399.000 |
|??? 4899.000 |
|??? 2799.000 |
+-------------+
3 rows in set (0.00 sec)????????

為什么查詢goods_cate=‘超極本’會(huì)出現(xiàn)Empty set (0.00 sec) 這種情況？