I'm trying to write a check constraint that uses a sub-query. Admittedly it's not the ideal solution, but to date it's the solution I've got to work with. Consider the following example table that is sufficiently similar to the real thing for sake of illustration:

CREATE TABLE ExampleTable (
    ExampleId INTEGER NOT NULL DEFAULT AUTOINCREMENT,
    KeyName NVARCHAR(50) NOT NULL,
    KeyValue INTEGER NOT NULL,

    -- Various other fields go here

    CONSTRAINT "PK_ExampleTable" PRIMARY KEY CLUSTERED ("ExampleId" ASC)
)

I have to write a constraint that ensures that the supplied KeyName and KeyValue data, along with various particular combinations of the other fields, do not already occur within the same table. The sort of constraint I've developed for this is like the following:

ALTER TABLE ExampleTable
ADD CONSTRAINT ExampleTableConstraint CHECK 
( 
    (SELECT COUNT(*) FROM ExampleTable AS SubQueryTable
        WHERE SubQueryTable.[KeyName] = [KeyName] AND
              SubQueryTable.[KeyValue] = [KeyValue] AND
              -- Other parameters go here
     ) = 0
)

The constraint can be created just fine, and it doesn't give any errors with the first row I insert into the table, but after that it fails every time no matter what completely unique values I supply for all the fields. Some time debugging has convinced me that this is because it's not disambiguating the column references and is simply comparing the columns to themselves in the sub-query. Or to put it differently, it seems to be working as if I had written the constraint as follows:

ALTER TABLE ExampleTable
ADD CONSTRAINT ExampleTableConstraint CHECK 
( 
    (SELECT COUNT(*) FROM ExampleTable AS SubQueryTable
        WHERE SubQueryTable.[KeyName] = SubQueryTable.[KeyName] AND
              SubQueryTable.[KeyValue] = SubQueryTable.[KeyValue] AND
              -- Other parameters go here
     ) = 0
)

This naturally would fail every row but the first, which is exactly what I'm seeing. Can anybody tell me how I might disambiguate my columns in a check constraint sub-query? Thanks in advance!