databaseintro(1grass) GRASS GIS User's Manual databaseintro(1grass)
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 man-
agement, while the v.db.* set of commands operates on the vector map
(see Vector introduction).
Available drivers
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 di-
rectly to the DBMS. For this reason, the SQLite driver is the default
DBMI backend.
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/data-
base 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 selec-
tively 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
SQL commands
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.
Managing the default DBMI settings
Per default vector map attributes are stored in SQLite tables. This de-
fault 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):
• 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.
Table maintenance
To drop a column from a selected attribute table, use db.dropcolumn.
With db.droptable an attribute table can be deleted.
Database Schema
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 data-
base.
Migrating to a different database engine
To migrate a GRASS database table (or a GRASS vector map) to a differ-
ent 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.
See also
• 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
SOURCE CODE
Available at: Database management in GRASS GIS source code (history)
Accessed: unknown
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