Код

CREATE FUNCTION dbo.Example(@s1 varchar(10), @s2 varchar(10))
RETURNS varchar(10)
BEGIN
	declare @a varchar(10)
	declare @i int

	set @i = 0
	while (substring(@s1,1,@i+1)=substring(@s2,1,@i+1)) and (@i<=len(@s1) or @i<len(@s2)) begin
		set @i = @i + 1
	end
	set @a = substring(@s1,1,@i)
RETURN @a
END 

Код

select dbo.Example(max(j.docno),min(j.docno))
from zayavki as z (nolock)
left join _1sjourn as j (nolock) on z.iddoc = j.iddoc
where etap = 3
and z.iddoc not in (select distinct iddoc from zayavki (nolock) where etap > 3)
and pechskl = 1 

Код

	SELECT
		MAX(CONVERT(int, CASE WHEN RowN=1 THEN
			CASE WHEN tmp.str6 LIKE tmp.str1+'%' THEN tmp.str1 END
		ELSE CASE WHEN RowN=2 THEN
			CASE WHEN tmp.str6 LIKE tmp.str2+'%' THEN tmp.str2 END
		ELSE CASE WHEN RowN=3 THEN
			CASE WHEN tmp.str6 LIKE tmp.str3+'%' THEN tmp.str3 END
		ELSE CASE WHEN RowN=4 THEN
			CASE WHEN tmp.str6 LIKE tmp.str4+'%' THEN tmp.str4 END
		ELSE CASE WHEN RowN=5 THEN
			CASE WHEN tmp.str6 LIKE tmp.str5+'%' THEN tmp.str5 END
		END END END END END)) as str
	FROM (
		SELECT
			LEFT(val.a,1) as str1,
			LEFT(val.a,2) as str2,
			LEFT(val.a,3) as str3,
			LEFT(val.a,4) as str4,
			LEFT(val.a,5) as str5,
			val.b as str6,
			RowNs.RowN
		FROM (
			select max(j.docno)	as a
			,	min(j.docno) as b
			from zayavki as z (nolock)
			left join _1sjourn as j (nolock) on z.iddoc = j.iddoc
			where etap = 3
			and z.iddoc not in (select distinct iddoc from zayavki (nolock) where etap > 3)
			and pechskl = 1
		) as val,
		(
			SELECT 1 as RowN
			 UNION ALL SELECT 2
			 UNION ALL SELECT 3
			 UNION ALL SELECT 4
			 UNION ALL SELECT 5
		) as RowNs
	) as tmp 

Код

Длина	= Мин(СтрДлина(МаксНомер), СтрДлина(МинНомер));
Поз	= Длина;