Database

WITH cte As
(
    SELECT
        ID,
        [Device id],
        TimeZone,
        [Effective Date],
        ROW_NUMBER() OVER 
        (
            PARTITION BY 
                [Device id] 
            ORDER BY
                CASE WHEN [Effective Date] <= @YourDateParameter THEN 0 ELSE 1 END,
                [Effective Date] DESC
        ) As RN
    FROM
        Timetable
)
SELECT
    ID,
    [Device id],
    TimeZone,
    [Effective Date]
FROM
    cte
WHERE
    RN = 1
;

ROW_NUMBER() OVER 
(
    PARTITION BY 
        [Device id] 
    ORDER BY
        CASE WHEN [Effective Date] <= @YourDateParameter THEN 0 ELSE 1 END,
        CASE WHEN [Effective Date] <= @YourDateParameter THEN [Effective Date] ELSE Null END DESC,
        CASE WHEN [Effective Date] <= @YourDateParameter THEN Null ELSE [Effective Date] END
) As RN

1. Dates on or before the date parameter come first;
2. Dates on or before the parameter are sorted in descending order, so the latest comes first;
3. Dates after the parameter are sorted in ascending order, so the earliest comes first;

bool b1= true;
bool b2= false;
bool res= b1 == b2;

(SQL != C++) && (SQL != C#)

(SQL != C++) && (SQL != C#)

a XOR b <==> (a AND (NOT b)) OR ((NOT a) AND b)

... WHERE ((TBL1.INTFIELD Is Null And TBL2.INTFIELD Is Not Null) Or (TBL1.INTFIELD Is Not Null And TBL2.INTFIELD Is Null))

// Since you said C#
from oh in context.Order_History
where oh.OrderDate ...

orderby oh.OrderNumber desc
group oh by oh.RequiredProperty in ohGrouped // RequireProperty is the property you want to use

... 
select ...

CASE

If code >= 1 AND <= 9 then place two zeros if front...001, 002....009
if code >= 10 AND <= 99 then place one zero if front....010, 050...,099

FORMAT(code, 'D3')

CASE
    WHEN code Between 1 And 9 THEN '00'
    WHEN code Between 10 And 99 THEN '0'
    ELSE ''
END + CAST(code As varchar(10))