Attributemanagementingeneral
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).
Availabledrivers
Available drivers are listed in SQL support in GRASS GIS.
Notes:
The DBF driver provides only very limited SQL support (as DBF is not an SQL DB) while the other DBMS
backends (such as SQLite, PostgreSQL, MySQL etc) provide full SQL support since the SQL commands are sent
directly to the DBMS. For this reason, the SQLite driver is the default DBMI backend.
DBconnectionmanagement
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.
Attributedataimportandexport
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:
• MDB Tools: Convert MS-Access data to SQL, DBF, etc.
• Using OpenOffice.org with SQL Databases
SQLcommands
GRASS supports two 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.
ManagingthedefaultDBMIsettings
Per default vector map attributes are stored in SQLite tables. This default definition can be modified
with db.connect. If an external DBMS is used, db.login may be required.
Creatingadatabase
Specific commands are explained on the individual driver pages (these pages are only available if driver
was compiled in this installation):
• DBF: see DBF page
• SQLite: SQLite page
• mySQL: mySQL and meSQL pages
• ODBC: ODBC page (connect to Oracle, etc.)
• PostgreSQL: PostgreSQL and PostGIS page
Metadata
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.
Tablemaintenance
To drop a column from a selected attribute table, use db.dropcolumn. With db.droptable an attribute
table can be deleted.
DatabaseSchema
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.
Migratingtoadifferentdatabaseengine
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.
Seealso
• Introduction into raster data processing
• Introduction into 3D raster data (voxel) processing
• Introduction into vector data processing
• Introduction into image processing
• Introduction into temporal data processing
• Projections and spatial transformations
• Graphical User Interface
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