MYSQL/ifnull

select distinct email from xxx where ifnull(email,'') = '';
+-------+
| email |
+-------+
| NULL  |
|       |
+-------+
2 rows in set (0.13 sec)


// Thanks.
NULLを空文字に変換
http://d.hatena.ne.jp/saw_yo/20110824/1314152369


empty