-- use APPLY to evaluate your filters

SELECT *

FROM table1

CROSS APPLY (

SELECT

Filter1 = CASE

WHEN @con = 0 AND YEARMONTH >= REPLACE(@YearMonth,'-','') THEN 1

WHEN YEARMONTH <> REPLACE(@YearMonth,'-','') THEN 2

ELSE NULL END,

Filter2 = CASE

WHEN @con = 0

AND CONVERT(datetime, RDATE, 103) >= convert(datetime, @dt3, 103)

AND CONVERT(datetime, MD.RDATE, 103) <= convert(datetime, @dt4, 103) THEN 1

WHEN CONVERT(datetime, RDATE, 103) >= convert(datetime, @dt1, 103)

AND CONVERT(datetime, MD.RDATE, 103) <= convert(datetime, @dt2, 103) THEN 2

ELSE NULL END

) x

WHERE id = @id

AND imtid <> 0

-- and to check they work as you expect them to

SELECT *

FROM table1

CROSS APPLY (

SELECT

Filter1 = CASE

WHEN @con = 0 AND YEARMONTH >= REPLACE(@YearMonth,'-','') THEN 1

WHEN YEARMONTH <> REPLACE(@YearMonth,'-','') THEN 2

ELSE NULL END,

Filter2 = CASE

WHEN @con = 0

AND CONVERT(datetime, RDATE, 103) >= convert(datetime, @dt3, 103)

AND CONVERT(datetime, MD.RDATE, 103) <= convert(datetime, @dt4, 103) THEN 1

WHEN CONVERT(datetime, RDATE, 103) >= convert(datetime, @dt1, 103)

AND CONVERT(datetime, MD.RDATE, 103) <= convert(datetime, @dt2, 103) THEN 2

ELSE NULL END

) x

WHERE id = @id

AND imtid <> 0

AND x.Filter1 = 1

AND x.Filter2 = 2

-- when you are absolutely sure everything is working as it should,

-- you can switch the filters back to the WHERE clause. You don't have to.

-- The execution plan is likely to be identical and retaining the APPLY block

-- aids readability.

SELECT *

FROM table1

WHERE id = @id

AND imtid <> 0

AND (CASE

WHEN @con = 0 AND YEARMONTH >= REPLACE(@YearMonth,'-','') THEN 1

WHEN YEARMONTH <> REPLACE(@YearMonth,'-','') THEN 2

ELSE NULL END) = 1

AND (CASE

WHEN @con = 0

AND CONVERT(datetime, RDATE, 103) >= convert(datetime, @dt3, 103)

AND CONVERT(datetime, MD.RDATE, 103) <= convert(datetime, @dt4, 103) THEN 1

WHEN CONVERT(datetime, RDATE, 103) >= convert(datetime, @dt1, 103)

AND CONVERT(datetime, MD.RDATE, 103) <= convert(datetime, @dt2, 103) THEN 2

ELSE NULL END) = 2

-- WARNING: using functions on your table columns will almost always prevent

-- SQL Server from using an index on those columns, resulting in suboptimal performance.