ISDATE working but ISNULL not working (as expected)?

I'm new to CFML so please excuse my ignorance.
I'm experimenting with ISDATE and ISNULL on a simple mysql table which as some NULL dates:
-- ----------------------------
-- Table structure for `temp`
-- ----------------------------
  `id` int(11) NOT NULL,
  `date` date DEFAULT NULL

-- ----------------------------
-- Records of temp
-- ----------------------------
INSERT INTO `temp` VALUES ('1', null);
INSERT INTO `temp` VALUES ('2', '2011-04-13');
INSERT INTO `temp` VALUES ('3', null);
INSERT INTO `temp` VALUES ('4', '2011-04-21');
INSERT INTO `temp` VALUES ('5', null);
INSERT INTO `temp` VALUES ('6', '2011-04-24');
INSERT INTO `temp` VALUES ('7', null);
INSERT INTO `temp` VALUES ('8', '2011-04-28');
INSERT INTO `temp` VALUES ('9', null);

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I then run the following in CFML:
<cfquery name="testing">select id, date from temp</cfquery>
<p>Temp table:</p>
<cfoutput query="testing">
#id# IsDate(date)=#IsDate(date)# IsNull(date)=#IsNull(date)#<br />

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and get the following output:
Temp table:

1 IsDate(date)=NO IsNull(date)=YES
2 IsDate(date)=YES IsNull(date)=YES
3 IsDate(date)=NO IsNull(date)=YES
4 IsDate(date)=YES IsNull(date)=YES
5 IsDate(date)=NO IsNull(date)=YES
6 IsDate(date)=YES IsNull(date)=YES
7 IsDate(date)=NO IsNull(date)=YES
8 IsDate(date)=YES IsNull(date)=YES
9 IsDate(date)=NO IsNull(date)=YES

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ISDATE works correctly, giving NO for NULL dates and YES for real dates.
What I do not understand is why ISNULL gives YES for all items -- I was expecting the opposite of ISDATE -- YES for NULL dates and NO for real dates.
What have I missed?
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
could you please try to `date` instead of date in the query
ShanghaiDAuthor Commented:
select `id`, `date` from `temp`

still gives same result.......
Guy Hengel [angelIII / a3]Billing EngineerCommented:
what about:
<cfquery name="testing">select id, date, IsNull(date) is_null, IsDate(date) is_date from temp</cfquery>
<p>Temp table:</p>
<cfoutput query="testing">
#id# IsDate(date)=#Is_Date# IsNull(date)=#Is_Null#<br />

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ShanghaiDAuthor Commented:
No,, that throws an error.  Function IsDate is a CFML function, not a MySQL function, so it cannot run in the cfquery tag.  
I have already confirmed that the odd id date values are NULL in MySQL, just to be sure, and running (in MySQL) simply:
SELECT id, date from temp
results in:

1      (null)
2      2011-04-13
3      (null)
4      2011-04-21
5      (null)
6      2011-04-24
7      (null)
8      2011-04-28
9      (null)
(as it should).

ShanghaiDAuthor Commented:
I also ran a simple cfdump of the query and got (as expected):
 <cfdump var="#testing#" abort="true">
Guy Hengel [angelIII / a3]Billing EngineerCommented:
sorry, I am not a CF specialist, actually (rather mysql)
<cfquery name="testing">select id, date, IsNull(date) is_null from temp</cfquery>
<p>Temp table:</p>
<cfoutput query="testing">
#id# IsDate(date)=#IsDate(date)# IsNull(date)=#Is_Null#<br />

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ShanghaiDAuthor Commented:
Your revised query gives correct output but it uses the MySQL IsNull function (in the query) rather than the CFML ISNULL function in handling the results of the query.

It seems to me that the CFML ISNULL function is treating the "empty string" as something other than a Null, and so is not showing output that I had expected.

I'll do some more research tomorrow at work (it's evening now in Shanghai).

Thanks for you input already.
You have to think of CF's new isNull() function much like  structKeyExists()

It is not testing to see if a database "NULL" value is NULL, coldfusion always handles NULL from the database as an empty string.  isNull() is not testing for empty strings, it is testing for the non-existance of a variable; such as IsDefined() and structkeyexists()

If you want to test if something is empty, the most efficient way is to use len()

<CFIF len(myQuery.value)>
   There is a value
   It is empty

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ShanghaiDAuthor Commented:
Thank you for your insight. I learn something new about CFML every day!
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