Thanks, although I don't think that works for me as one of the other contexts I need to access this LinkedFundsByPerson query are as a select query to to return those 4 columns in the original into a result set, and another context is I use it within a UNION query as suggested here: https://community.intersystems.com/post/possible-merge-two-resultset#com...

Then I get error

LITERAL ('CAST') expected, CAST found

It's like it's unable to process anything other than literal values as parameters for class queries called within SQL. A shame as I would like to avoid duplicating such queries

I tried with the parameter (or removing it from the query entirely),  but no change. Indeed, the error message only refers to the first parameter:

LITERAL ('PERSON') expected, IDENTIFIER (Person) found DECLARE QRS CURSOR FOR SELECT ...

If I send a literal value ('123') then everything works, but it doesn't seem to want to deal with a column reference, but I don't understand why if it can cope with that fine when I expand out the query? eg

SELECT Person.ExternalReference
FROM QUASAR_KYC_Person.Person Person
WHERE NOT EXISTS (

    SELECT Fund.InternalReference,Fund.ShortName,ISNULL(FundClosure.ClosureStatus,'Open') AS ClosureStatus,'P' AS Linktype
    FROM QUASAR_Core_Client.Client AS Client
    INNER JOIN QUASAR_KYC_Fund.Fund AS Fund ON Client.Number=Fund.InternalReference
    LEFT JOIN QUASAR_GDPR_Close_Fund.FundClosure As FundClosure ON Client.Number=FundClosure.ID
    WHERE Client.ClientMarketIndicator='C'
    AND Client.Number IN
    (
        SELECT Client
        FROM QUASAR_KYC_Person.FundLink
        WHERE Person->InternalReference=Person.ID
    )

)

Hi, Thanks! I get the same error when doing a WHERE 0< ...

CUSTOM_MyQuery is a SELECT statement with a parameter. It seems to work fine if I pass in a value, but now a column reference, but I'm not sure why? What's strange is if I replace the call to CUSTOM_MyQuery with the whole contents of that SELECT statement, with TableA.ID instead of the parameter, it works.

My real-world CUSTOM_MyQuery is 

/// Linked Funds via Person->Fund link
Query LinkedFundsByPerson(personId As %Library.Integer, RWOOnly As %Library.Boolean) As %Library.SQLQuery(CONTAINID = 0, ROWSPEC = "Number:%Integer, Name:%String, Status:%String, LinkType:%String")
{
SELECT Fund.InternalReference,Fund.ShortName,ISNULL(FundClosure.ClosureStatus,'Open') AS ClosureStatus,'P' AS Linktype
FROM QUASAR_Core_Client.Client AS Client
INNER JOIN QUASAR_KYC_Fund.Fund AS Fund ON Client.Number=Fund.InternalReference
LEFT JOIN QUASAR_GDPR_Close_Fund.FundClosure As FundClosure ON Client.Number=FundClosure.ID
WHERE Client.ClientMarketIndicator='C'
AND Client.Number IN
(
SELECT Client
FROM QUASAR_KYC_Person.FundLink
WHERE Person->InternalReference=:personId
)
}

(the second parameter isn't used but is there for legacy reasons - doesn't seem to matter if I remove it)

If I use a class query in an EXISTS clause like:

SELECT *
FROM TableA
WHERE EXISTS (SELECT * FROM CUSTOM_MyQuery(TableA.ID))

I get an error of the type:

LITERAL ('TABLEA') expected, IDENTIFIER (TABLE) found DECLARE QRS CURSOR FOR ...

Is there a way around this?

Thanks,
Chris