How to update null into a column type Date in MySQL ?

Question

I have a table in Mysql DB like following

mysql> describe APPTBL;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| APP_ID      | int(11)     | NO   | PRI | NULL    | auto_increment |
| CREATE_DATE | date        | YES  |     | NULL    |                |
| CLOSE_DATE  | date        | YES  |     | NULL    |                |
| ACTION      | text        | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+

While Starting of App, i am inserting the app details with CREATE_DATE and when it is closing, i am updating its CLOSE_DATE. But in case if user is restarting the app, i want to update NULL in place of CLOSE_DATE column. Here is my query,

mysql> update APPTBL set CLOSE_DATE = NULL where APP_ID = 1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0
mysql> select * from APPTBL ;
+-----------+-------------+------------+------------+
|   APP_ID  | CREATE_DATE | CLOSE_DATE |   ACTION   |
+-----------+-------------+------------+------------+
|    1      |  2013-10-08 | NULL       | XXXXXYYYYY |
+-----------+-------------+------------+------------+
1 row in set (0.00 sec)

But why i am not getting any result in this??

mysql> select * from APPTBL where CLOSE_DATE = NULL;
Empty set (0.00 sec)

Also, as i am writhing a java program using this where

rs = st.executeQuery("update APPTBL set CLOSE_DATE = NULL where APP_ID = 1");
if(!rs.wasNull()){
   // Why it is coming here??
}

Answer 1

I found the issue. We can not use wasNull() directly in java like i did previously. By default it will return false only. So, We need to get some value and then have to check whether last value is NULL or not by using wasNull function.

if(rs.next())
    myValue = rs.getString(1);
if(rs.wasNull()){ 
    // Here comes resultset with null value only
}

Thanks for support @Salil

Answer 2

try IS NULL operator i.e. "select * from APPTBL where CLOSE_DATE IS NULL"