Make sure that each of the commented subqueries returns no more than 1 value.

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>It is late and my brain is not functioning... The below listed query returns the following error message after adding lines of code that are currently commented out:
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>Subquery returned more than 1 value. This is not permitted when the subquery follows

=, !=, <, <= , >, >=

or when the subquery is used as an expression.
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>How can I modify this query to prevent this error?
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>Thank you,
>Daniel
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>

>Select Distinct prtnum, 
>Coalesce((Select curqty from lens_invsum Lens where lens.prtnum = Lens_invsum.prtnum and invsts = 'R' and sitnam ='NJ'), 0) as NJUsable,
>Coalesce((Select curqty from lens_invsum Lens where lens.prtnum = Lens_invsum.prtnum and invsts = 'R' and sitnam ='NV'), 0) as NVUsable,
>--Coalesce((Select curqty from lens_invsum Lens where lens.prtnum = Lens_invsum.prtnum and invsts <> 'R' and sitnam ='NJ'), 0) as NJNotUseable,
>--Coalesce((Select curqty from lens_invsum Lens where lens.prtnum = Lens_invsum.prtnum and invsts <> 'R' and sitnam ='NV'), 0) as NVNotUseable
>from Lens_invsum
>Order by prtnum
>