It doesn't help much because you may not need UDF after all. Anyway, there're a couple ways to implement such UDF()

-- #1
if @module='MV'
        SELECT @judgecode= mv_judge FROM motorvehicle
        WHERE keyident = @keyident
else if @module='LL'
        SELECT @judgecode= ll_judge FROM locallaw
        WHERE keyident = @keyident
else if @module='CV'
        SELECT @judgecode=civ_judge FROM civil
        WHERE keyident = @keyident
else if @module='CRM'
        SELECT @judgecode=crm_judge FROM criminal
        WHERE keyident = @keyident
else if @module='SC'
        SELECT @judgecode=sc_judge FROM smallclaims
        WHERE keyident = @keyident

RETURN (@judgecode)
---------------------------------------------------
-- #2
SELECT @judgecode= mv_judge FROM motorvehicle
	WHERE @module='MV' AND keyident = @keyident
UNION ALL	
SELECT @judgecode= ll_judge FROM locallaw
	WHERE @module='LL' AND keyident = @keyident
...

UNION ALL	
SELECT @judgecode=sc_judge FROM smallclaims
        WHERE @module='SC' AND keyident = @keyident
RETURN (@judgecode)

Please enclose your code in < pre> and < /pre> tags (w/o spaces) so it's easier to read.

>Ok here is my scalar UDF

>CREATE FUNCTION fn_getjudge(@module char(10), @keyident nvarchar (12))
>RETURNS char(3)
>begin
>DECLARE @judgecode Char(3)
>  SET @judgecode=''
>if @module='MV'
>        SELECT @judgecode= mv_judge FROM motorvehicle
>        WHERE keyident = @keyident
>RETURN (@judgecode)
>if @module='LL'
>        SELECT @judgecode= ll_judge FROM locallaw
>        WHERE keyident = @keyident
>RETURN (@judgecode)
>if @module='CV'
>        SELECT @judgecode=civ_judge FROM civil
>        WHERE keyident = @keyident
>RETURN (@judgecode)
>if @module='CRM'
>        SELECT @judgecode=crm_judge FROM criminal
>        WHERE keyident = @keyident
>RETURN (@judgecode)
>if @module='SC'
>        SELECT @judgecode=sc_judge FROM smallclaims
>        WHERE keyident = @keyident
>RETURN (@judgecode)
>end