Database management in GRASS GIS
Attribute management in general
GRASS can be linked to one or many database management systems (DBMS).
The db.* set of commands provides basic SQL support for
attribute management, while the v.db.* set of commands operates
on the vector map (see Vector introduction).
Available drivers are listed in SQL support in GRASS GIS.
The default DBF driver provides only very limited SQL
support (as DBF is not an SQL DB) while the other DBMS backends (such
as PostgreSQL, MySQL etc) provide full SQL support since the SQL
commands are sent directly to the DBMS.
DB connection management
The current database management settings are shown or modified with
db.connect for current mapset. Available DBMI drivers
are listed with db.drivers. Some DBMI backends
require a user/password for driver/database to be set with db.login.
In order to test a driver, run db.test.
Attribute data import and export
Attribute data can be imported with db.in.ogr from
various formats and exported with db.out.ogr. To internally
copy a a full table or selectively parts of it, use db.copy.
Further conversion tools:
GRASS supports to main SQL operations, execution of an SQL statement
(db.execute) and selection
of data from a table (db.select).
See the SQL help page for examples.
Managing the default DBMI settings
Per default vector map attributes are stored in DBF table files. This default
definition can be modified with db.connect. If an
external DBMS is used, db.login may be required.
Creating a database
Specific commands are explained on the individual driver pages (these
pages are only available if driver was compiled in this installation):
All columns for a given table are listed with db.columns.
The command db.describe describes a table in detail. To
list all available tables for a given database, run db.tables.
To drop a column from a selected attribute table, use db.dropcol.
With db.droptable an attribute table can be deleted.
Currently schema support only works for PostgreSQL connections. Default schema
can be set with db.connect. Note that the default
schema will be used by all db.* modules.
db.tables returns 'schema.table' if schemas are
available in the database.
Migrating to a different database engine
To migrate a GRASS database table (or a GRASS vector map) to a different DBMI engine,
the best solution is to create a new MAPSET, define the DBMI settings accordingly
with db.connect and if needed, db.login.
Then the table of interest can be copied over with db.copy from
the original MAPSET. Likewise, a vector map including its table(s) are copied from
the original MAPSET to the current MAPSET with g.copy.
Main index -
database index -
© 2003-2012 GRASS Development Team