[GRASS-user] Re: [GRASS-dev] trying to update column with another text column

[Moritz Lennert]

On 04/04/12 08:02, Michael Barton wrote:
> I want to update a column with the value of another column. I am using
> v.db.update.
>
> The docs say that I can update a column with the value of another column
> by specifying that column in the value field. In fact, if I put the
> names of numeric columns, this works fine (e.g., v.db.update
> map=myvector layer=1 column=summary value=col3 + col4).
>
> But if I do something like this for a string column, I simply get the
> string of the name of the column (e.g., v.db.update map=myvector layer=1
> column=summary value=col5 put "col5" into the summary column, NOT the
> strings that are STORED in col5).
>
> Are the docs wrong or is this a bug?

When the column to update is a string column, the script surrounds the 
value given with the value= parameter with quotes. It could check 
whether the given value is a column name and then not quote it but then 
again, how can we know that the person does not what to just fill a 
column with a string that corresponds to the name of another column ?

Try using the qcolumn parameter.

So docs should be updated to reflect that.

Moritz