mysqlnull和‘’

mysql> select goods_name from goods where goods_name is not null limit 3;
+--------------------+
| goods_name |
+--------------------+
| KD876 | 
| htcN85原装充电器 | 
| 诺基亚原装5800耳机 | 
+--------------------+

3 rows in set (0.00 sec)

mysql> select goods_name from goods where goods_name is null ;
Empty set (0.00 sec)

null 遇见运算符 一律返回null

mysql> select goods_name from goods where goods_name=null ;
Empty set (0.00 sec)

mysql> select goods_name from goods where goods_name!=null ;
Empty set (0.00 sec)

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