there is a end_date column record with date/time datatype, how could i query datat that showing the particular is empty.
i try end_date = NULL, no record is showing and end_date = ' ' , datatype mismatch... so which one should i write??

Use Is Null

For example:

SELECT [Work Request].[START DATE]
FROM [Work Request]
WHERE ((([Work Request].[START DATE]) Is Null));

Use Is Null

For example:

SELECT [Work Request].[START DATE]
FROM [Work Request]
WHERE ((([Work Request].[START DATE]) Is Null));

is it "IS NULL" and "IS NOT NULL" same with " = NULL" and "<> NULL"?

=null and <> null do not work.
for queries use ColumnName is null

for vba code use isNull(ColumnName)

to negate use the not operator
eg

Not IsNull(ColumnName)