Qual è il modo più efficiente per normalizzare il testo da una colonna a una tabella?

Se hai un numero massimo di colonne, un po' di XML all'interno di CROSS APPLY.

Se sconosciuto, dovresti passare a DYNAMIC.

Esempio

Declare @YourTable Table ([ID] varchar(50),[SomeCol] varchar(50))
Insert Into @YourTable Values 
 (1,'[Key1:Value1:Value2:Value3:Value4:Value5]')
,(2,'[Key2:Value1:Value2:Value3:Value4:Value5]')
,(3,'[Key3:Value1:Value2:Value3:Value4:Value5]')

Select A.ID
      ,B.*
 From  @YourTable A
 Cross Apply (
                Select Pos1 = ltrim(rtrim(xDim.value('/x[1]','varchar(max)')))
                      ,Pos2 = ltrim(rtrim(xDim.value('/x[2]','varchar(max)')))
                      ,Pos3 = ltrim(rtrim(xDim.value('/x[3]','varchar(max)')))
                      ,Pos4 = ltrim(rtrim(xDim.value('/x[4]','varchar(max)')))
                      ,Pos5 = ltrim(rtrim(xDim.value('/x[5]','varchar(max)')))
                      ,Pos6 = ltrim(rtrim(xDim.value('/x[6]','varchar(max)')))
                      ,Pos7 = ltrim(rtrim(xDim.value('/x[7]','varchar(max)')))
                      ,Pos8 = ltrim(rtrim(xDim.value('/x[8]','varchar(max)')))
                      ,Pos9 = ltrim(rtrim(xDim.value('/x[9]','varchar(max)')))
                From  (Select Cast('<x>' + replace(replace(replace(SomeCol,'[',''),']',''),':','</x><x>')+'</x>' as xml) as xDim) as A 
             ) B

Resi

ID  Pos1    Pos2    Pos3    Pos4    Pos5    Pos6    Pos7    Pos8    Pos9
1   Key1    Value1  Value2  Value3  Value4  Value5  NULL    NULL    NULL
2   Key2    Value1  Value2  Value3  Value4  Value5  NULL    NULL    NULL
3   Key3    Value1  Value2  Value3  Value4  Value5  NULL    NULL    NULL

Dovrei aggiungere, il ltrim(rtrim(...)) è facoltativo e il varchar(max) è il mio valore predefinito dimostrativo.

Declare @S varchar(max)='
[Key1:Value1:Value2:Value3:Value4:Value5]
[Key2:Value1:Value2:Value3:Value4:Value5]
[Key3:Value1:Value2:Value3:Value4:Value5]
'

Select B.*
 From  (
        Select RetSeq = Row_Number() over (Order By (Select null))
              ,RetVal = LTrim(RTrim(B.i.value('(./text())[1]', 'varchar(max)')))
        From  (Select x = Cast('<x>' + replace(@S,char(13)+char(10),'</x><x>')+'</x>' as xml).query('.')) as A 
        Cross Apply x.nodes('x') AS B(i)
       ) A
 Cross Apply (
               Select  Pos1 = ltrim(rtrim(xDim.value('/x[1]','varchar(max)')))
                      ,Pos2 = ltrim(rtrim(xDim.value('/x[2]','varchar(max)')))
                      ,Pos3 = ltrim(rtrim(xDim.value('/x[3]','varchar(max)')))
                      ,Pos4 = ltrim(rtrim(xDim.value('/x[4]','varchar(max)')))
                      ,Pos5 = ltrim(rtrim(xDim.value('/x[5]','varchar(max)')))
                      ,Pos6 = ltrim(rtrim(xDim.value('/x[6]','varchar(max)')))
                      ,Pos7 = ltrim(rtrim(xDim.value('/x[7]','varchar(max)')))
                      ,Pos8 = ltrim(rtrim(xDim.value('/x[8]','varchar(max)')))
                      ,Pos9 = ltrim(rtrim(xDim.value('/x[9]','varchar(max)')))
                From  (Select Cast('<x>' + replace(replace(replace(RetVal,'[',''),']',''),':','</x><x>')+'</x>' as xml) as xDim) as A 
       ) B
 Where A.RetVal is not null