M code nullable values

[Dicken]

Hi, 

I have a simple two column table a = text b = numbers,   
i have added two columns , 

Table.AddColumn( Source, "N", each
Type.IsNullable(
Value.Type( [B] )))

I have been trying to use Table.ColumnsOfType, and I don't really unserstand the nullable aspect , 

As I understand the Change type step values applied are nullable, ( even though  it will have text not nullable text ) 
so if i use  

= Table.ColumnsOfType( 
 #table( type table [ A = text ] , { { "abc"} } ), 
 { type text } )

This works but I get into difficulty  when importing a 'reall' table   can some one give me a some help /  reading suggestion, 
I've read quite a bit on Type is nullable, and it seems contradict itself and makes my head hurt.
Richard. 

[ronrsnfld]

Also note you can determine whether a column type is nullable or not by inspecting the isNullable column of the output from Table.Schema

[Dicken]

Yes, I have a question re schema, but I need to work  to get  put an example together, 

but thanks for  repsonding.

[ronrsnfld · Accepted solution]

To return columns of type number, try:

Table.ColumnsOfType(Source,{type nullable number})