Question

I have field in MySQL table which i set it to default value as timestamp,when I update it first time it get update to current timestamp and when I update it second time then also it get update to current timestamp bt when I update the same third time with same value in column timestamp field not get update to current timestamp.

My table structure is:

+-----------+-----------+------+-----+-------------------+-----------------------------+
| Field     | Type      | Null | Key | Default           | Extra                       |
+-----------+-----------+------+-----+-------------------+-----------------------------+
| EID       | int(11)   | NO   | PRI | 0                 |                             |
| MOD_EID   | int(11)   | YES  |     | NULL              |                             |
| EXIT_TIME | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-----------+-----------+------+-----+-------------------+-----------------------------+

when I update first time I am inserting required value in EID and 0 in MOD_EID. When I update second time I am updating MOD_EID with required value. In both cases I able to get current_timestamp in EXIT_TIME.
But when I update MOD_EID field again with the same value after minute or one day , EXIT_TIME field not getting update to current_timestamp?
what’s wrong

The code for update is

String vexit=request.getParameter("string");

StringTokenizer tok=new StringTokenizer(vexit,"");

String sql,query,query2;
int count2=0;


    while(tok.hasMoreTokens())
    {
            String ide=tok.nextToken();
sql="SELECT count(EID) FROM tm_exit where EID='"+ide+"' ";
            ResultSet rs=st.executeQuery(sql);
            while(rs.next())
            {
            count2=rs.getInt(1);
}
        if(count2 >0)
            {
query="UPDATE tm_exit set MOD_EID='"+ide+"' WHERE EID='"+ide+"'";
int flag=st.executeUpdate(query);
}
        else
            {
query2="INSERT INTO tm_exit (EID,MOD_EID)values('"+ide+"',0)";
int flag2=st.executeUpdate(query2);
}
    }

Answer 1

A TIMESTAMP column is only updated automatically if the value of some other column changes. If you set MOD_EID to the same value as it already had, the TIMESTAMP won’t be updated. I don’t know why it used to work for you, here’s what the documentation says:

If the column is auto-updated, it is automatically updated to the
current timestamp when the value of any other column in the row is
changed from its current value. The column remains unchanged if all
other columns are set to their current values. To prevent the column
from updating when other columns change, explicitly set it to its
current value. To update the column even when other columns do not
change, explicitly set it to the value it should have (for example,
set it to CURRENT_TIMESTAMP).