Calcular codigo de barras con T-SQL

Este query consta de cuatro subconsultas, la primera mas profunda, es para normalizar la referencia obtenida del servidor, es decir, que tenga un minimo y maximo de 21 digitos, despues la que separa los digitos uno a uno y multiplicando por dos los digitos en lugares impares y dejando intactos los que estan en lugares pares, el siguiente modulo verifica que los numeros obtenidos de la operacion anterios sobre los digitos en posicion par no sean superiores o iguales a diez, en caso verdadero suma los dos valores de cada resultado para dejarlos en un solo digito, y por ultimo, la consulta superior se encarga de concatenar cada uno de los digitos obtenidos de esta ultima operacion y calcular el digito de control de errores, facil no?

Select
numCliente
,Rtrim(Convert(Char,Ref)) +
Rtrim
(Convert
(Char,
(Case
When ([1]+[2]+[3]+[4]+[5]+[6]+[7]+[8]+[9]+[10]+[11]+[12]+[13]+[14]+[15]+[16]+[17]+[18]+[19]+[20]+[21]) % 10 = 0
Then 0
Else (10 - ([1]+[2]+[3]+[4]+[5]+[6]+[7]+[8]+[9]+[10]+[11]+[12]+[13]+[14]+[15]+[16]+[17]+[18]+[19]+[20]+[21]) % 10)
End
)
)
) As Codigo_De_Barras
From
(
Select
numCliente
,Ref
, [1] = (Case When A >= 10 Then Convert(Int,(Left(A,1)) + Convert(Int,Right(A,1))) Else A End)
, [2] = B
, [3] = (Case When C >= 10 Then Convert(Int,(Left(C,1)) + Convert(Int,Right(C,1))) Else C End)
, [4] = D
, [5] = (Case When E >= 10 Then Convert(Int,(Left(E,1)) + Convert(Int,Right(E,1))) Else E End)
, [6] = F
, [7] = (Case When G >= 10 Then Convert(Int,(Left(G,1)) + Convert(Int,Right(G,1))) Else G End)
, [8] = H
, [9] = (Case When I >= 10 Then Convert(Int,(Left(I,1)) + Convert(Int,Right(I,1))) Else I End)
,[10] = J
,[11] = (Case When K >= 10 Then Convert(Int,(Left(K,1)) + Convert(Int,Right(K,1))) Else K End)
,[12] = L
,[13] = (Case When M >= 10 Then Convert(Int,(Left(M,1)) + Convert(Int,Right(M,1))) Else M End)
,[14] = N
,[15] = (Case When O >= 10 Then Convert(Int,(Left(O,1)) + Convert(Int,Right(O,1))) Else O End)
,[16] = P
,[17] = (Case When Q >= 10 Then Convert(Int,(Left(Q,1)) + Convert(Int,Right(Q,1))) Else Q End)
,[18] = R
,[19] = (Case When S >= 10 Then Convert(Int,(Left(S,1)) + Convert(Int,Right(S,1))) Else S End)
,[20] = T
,[21] = (Case When U >= 10 Then Convert(Int,(Left(U,1)) + Convert(Int,Right(U,1))) Else U End)
From
(
Select
numCliente
,Ref
,Right(Left(Ref, 1),1) * 2 As A
,Right(Left(Ref, 2),1) As B
,Right(Left(Ref, 3),1) * 2 As C
,Right(Left(Ref, 4),1) As D
,Right(Left(Ref, 5),1) * 2 As E
,Right(Left(Ref, 6),1) As F
,Right(Left(Ref, 7),1) * 2 As G
,Right(Left(Ref, 8),1) As H
,Right(Left(Ref, 9),1) * 2 As I
,Right(Left(Ref,10),1) As J
,Right(Left(Ref,11),1) * 2 As K
,Right(Left(Ref,12),1) As L
,Right(Left(Ref,13),1) * 2 As M
,Right(Left(Ref,14),1) As N
,Right(Left(Ref,15),1) * 2 As O
,Right(Left(Ref,16),1) As P
,Right(Left(Ref,17),1) * 2 As Q
,Right(Left(Ref,18),1) As R
,Right(Left(Ref,19),1) * 2 As S
,Right(Left(Ref,20),1) As T
,Right(Left(Ref,21),1) * 2 As U
From
(
Select distinct
numCliente
,numReferencia
,'09' +
(Case Len(numReferencia)
When 5 Then '00000000000000'
When 6 Then '0000000000000'
When 7 Then '000000000000'
When 8 Then '00000000000'
When 9 Then '0000000000'
End) +
Ltrim(Rtrim(Convert(Char,numReferencia))) As Ref
From
cxcobrar B
where
numReferencia is not null
and len(numReferencia) >= 5
and len(numReferencia) <= 9
) As Obtiene_Datos
) As Calcula_Valores
) As Obtiene_Verificador
Where
numCliente In
()