SQL Server 2022

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-- All four columns must always contain the same value
CREATE TABLE dbo.Nums
(
    n1 bigint NOT NULL,
    n2 bigint NOT NULL,
    n3 bigint NOT NULL,
    n4 bigint NOT NULL,

    CONSTRAINT [PK dbo.Nums n1]
        PRIMARY KEY CLUSTERED (n1),

    CONSTRAINT [CK dbo.Nums all equal]
        CHECK (n1 = n2 AND n2 = n3 AND n3 = n4)
);
-- Populate with 64K rows, numbers 1-65536
WITH 
    N AS
    (
        SELECT n = ROW_NUMBER() OVER (ORDER BY @@PROCID) 
        FROM master.dbo.spt_values AS SV1
        CROSS JOIN master.dbo.spt_values AS SV2
        WHERE SV1.[type] = N'P'
        AND SV2.[type] = N'P'
        AND SV1.number BETWEEN 1 AND 256
        AND SV2.number BETWEEN 1 AND 256
    )
INSERT dbo.Nums WITH (TABLOCKX)
    (n1, n2, n3, n4)
SELECT
    N.n, N.n, N.n, N.n
FROM N;
65536 rows affected

CREATE OR ALTER FUNCTION dbo.F ()
RETURNS varchar(8000)
WITH INLINE = ON, SCHEMABINDING
AS
BEGIN
    DECLARE 
        @n1 integer, 
        @n2 integer,
        @n3 integer,
        @n4 integer;

    -- Column values from the selected row *must* all be the same
    SELECT
        @n1 = N.n1, 
        @n2 = N.n2,
        @n3 = N.n3,
        @n4 = N.n4
    FROM dbo.Nums AS N 
        TABLESAMPLE SYSTEM (35 PERCENT)
    ORDER BY
        N.n1 ASC
        OFFSET 0 ROWS
        FETCH NEXT 1 ROW ONLY
    OPTION (MAXDOP 1);

    -- Show the four numbers
    RETURN CONCAT_WS(' || ', @n1, @n2, @n3, @n4);
END;
-- All values the same with inlining disabled
SELECT pass = dbo.F() 
OPTION (USE HINT ('DISABLE_TSQL_SCALAR_UDF_INLINING'));


pass


883 || 883 || 883 || 883


-- Often different
SET TRANSACTION ISOLATION LEVEL SNAPSHOT;
BEGIN TRANSACTION;
SELECT fail = dbo.F();
COMMIT TRANSACTION;


fail


1 || 1 || 1 || 442