On 14/01/09 10:19, maning sambale wrote:
On Wed, Jan 14, 2009 at 5:02 PM, Glynn Clements
<gl...@gclements.plus.com> wrote:
Nikos Alexandris wrote:
The columns produces by v.extract are of type "CHARACTER" and v.dissolve
does not like this. It's an "old" issue. Can someone explain why it
becomes CHARACTER since grass' type for strings is "varchar"?
Regards, Nikos
Sorry, wrong question - false alarm.
Actually, the *real* question I have asked in the past but never really
got a reply is: why "sqlitebrowser" reports the columns as "varchar"
while db.describe reports (in grass-shell) the same columns to be of
type "CHARACTER"?
GRASS' DBMI doesn't distinguish CHARACTER from CHARACTER VARYING (aka
VARCHAR); the constant DB_SQL_TYPE_CHARACTER is used for both
(although there is also DB_SQL_TYPE_TEXT for TEXT).
Also, SQLite doesn't really have column types; it assigns types to
individual values rather than to columns. Columns may have a type of
SQLITE_INTEGER, SQLITE_FLOAT, SQLITE_TEXT, SQLITE_BLOB or SQLITE_NULL,
AFAIK, columns can have any "type", even ones invented by you. I.e.
create table test (key int, chartest ThisIsMyTextType);
works in sqlite, where "works" means that sqlite just ignores the column
"type" and automatically affects a type amongst the ones listed by Glynn
to each value.
but it doesn't actually require that the values' types conform to the
type.
A bit off-topic. Does this mean I can actually edit vector data
attributes as text even if the column is an INTEGER?
I'm using Sqlite database browser for editing. A bit dangerous for
me.
Yes. I find SQLite a bit dangerous because of that, especially since
GRASS enforces types.
> Any other way to add checks/controls for editing mistakes?
IMHO, the best way to deal with attributes in GRASS + SQLite is to do it
via the built-in tools in GRASS, and not via the SQLiteBrowser or other
tools as this can lead to incompatibilities and confusion. The new wxgui
has a very nice interface for attribute and table management.
Moritz
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