Blank "time" fields showing up as zeroes instead of blank

[bunner_bob]

I'm inputting times into a MySQL TIME format field. Things work as expected if any valid time is entered into my form, but if I leave my "time" form field blank, the database ends up with 00:00:00 for that time. This translates into midnight, which is obviously not the same as no time at all.

How can I keep these fields blank? I can't do if($starttime = 0) because then midnight won't work.

Relevant parts of the code:

<input type="Text" name="starttime" size="24" value="<?php echo $starttime ?>"></font></p>
<input type="Submit" name="submit" value="Add event date">&nbsp;<input type="reset" value="Undo my changes">

$sql = "INSERT INTO cpeventdates (eventid, startdate, enddate, starttime, endtime) VALUES ('$eventid','$startdate','$enddate','$starttime','$endtime')";
$result = mysql_query($sql);

Another somewhat related question - is there a neat way to translate between user-input 12-hour time format (plus, say, a radiobutton for am/pm) and 24-hour MySQL TIME format, and back again? I can just work out something with adding/subtracting 12 depending on what the current value/radiobutton says, but if there's a pre-existing function for that it'll save some time.

[Lars_Berg]

insert null if the field is left empty

$sql = "INSERT INTO cpeventdates (eventid, startdate, enddate, starttime, endtime) VALUES ("
if ( $startdate == "" ) {
$sql .= "null"
} else {
$sql .= "'" . $startdate . "'"
}
//etc

[bunner_bob]

Thanks for the response. I'm not entirely clear on the syntax of your reply.

Are you saying I replace the VALUE

'$startdate'

with the VALUE
'if($startdate==""){
$sql.="null"
}else{
$sql.="'".$startdate."'"
}'

in this line
$sql = "INSERT INTO cpeventdates (eventid, startdate, enddate, starttime, endtime) VALUES ('$eventid','$startdate','$enddate','$starttime','$endtime')";

???

As it stands it gives me syntax errors.

[Sxooter]

Close, but no banana... :-)

The syntax for NULL is that it is not quoted. i.e. the insert should look something like this::

insert into table (field1) values (NULL);

[bunner_bob]

Sorry - it's raw newbie time for me.

I keep getting a syntax error:
Parse error: parse error, unexpected '\"' in /Library/WebServer/Documents/carepartnership/admin/addevent.php on line 134

My code looks like this:

$sql = "INSERT INTO cpeventdates (eventid, startdate, enddate, starttime, endtime) VALUES ('$eventid','$startdate',
					if ($enddate == "") {
					$sql .= "null"
					} else {
					$sql .= "'" . $enddate . "'"
					} 
					,'$starttime','$endtime')";

The original code looked like this (and worked, except for the null value problem):

$sql = "INSERT INTO cpeventdates (eventid, startdate, enddate, starttime, endtime) VALUES ('$eventid','$startdate','$enddate','$starttime','$endtime')";

Hmmm...

[bunner_bob]

I understand a little more now - it's got to be null without quotes:

$sql = "INSERT INTO cpeventdates (eventid,startdate,enddate,starttime,endtime) VALUES ('$eventid','$startdate',null,'$starttime','$endtime')";

and not null with quotes:

$sql = "INSERT INTO cpeventdates (eventid,startdate,enddate,starttime,endtime) VALUES ('$eventid','$startdate','null','$starttime','
$endtime')";

Of course it's easy enough to type it in, and easy enough to get "null" in quotes, but how to phrase it so that IF $enddate == "", it sticks in null WITHOUT quotes - that's hurting my brain.

I can see how Lars' suggestion would work - sort of. I don't understand the syntax though - why the multiple "$sql"s, and just how to make it stop erroring.

Can someone help me get my syntax straight?