GRASS logo

SQL support in GRASS GIS

GRASS can use various RDBMS and embedded databases. SQL queries are directly passed to the underlying database system. The set of supported SQL commands depends on the RDMBS and driver selected.


The list of available drivers can vary in various binary distributions of GRASS.

dbfDBF files. Data are stored in DBF files.
sqliteSQLite embedded database.
pgPostgreSQL RDBMS.
mesqlMySQL embedded database.
odbcUnixODBC. (PostgreSQL, Oracle, etc.)



Display all vector points except for LAMAR valley and extensive trapping (brackets are superfluous in this example):
d.vect trapping_sites_points fcol=black icon=basic/diamond col=white size=13 \
    where="valley <> 'LAMAR' OR (valley = 'LAMAR' AND description = 'extensive trapping')"

Select all attributes from table where str1 column values are not 'No Name':

echo "SELECT * FROM archsites WHERE str1 <> 'No Name'" |

Example of subquery expressions from a list (does not work for DBF driver): mysites where="id IN ('P04', 'P05')"

Example of pattern matching:

# match exactly number of characters (here: 2), does not work for DBF driver: mysites where="id LIKE 'P__'"

#define wildcard: mysites where="id LIKE 'P%'"

Example of null handling:

v.db.addcol map=roads col="nulltest int"
v.db.update map=roads col=nulltest value=1 where="cat > 2"
d.vect roads where="nulltest is null"
v.db.update map=roads col=nulltest value=2 where="cat <= 2"

Examples of complex expressions in updates (using v.db.* modules):

v.db.addcol map=roads col="exprtest double precision"
v.db.update map=roads col=exprtest value=cat/nulltest
v.db.update map=roads col=exprtest value=cat/nulltest+cat where=cat=1

Examples of complex expressions in updates (using db.* modules):

echo "UPDATE roads SET exprtest=null"
echo "UPDATE roads SET exprtest=cat/2" | db.execute
echo "UPDATE roads SET exprtest=cat/2+cat/3" | db.execute
echo "UPDATE roads SET exprtest=NULL WHERE cat>2" | db.execute
echo "UPDATE roads SET exprtest=cat/3*(cat+1) WHERE exprtest IS NULL" | db.execute"

Instead of creating and updating new columns with an expression, you can use the expression directly in a command:

d.vect roads where="(cat/3*(cat+1))>8"
d.vect roads where="cat>exprtest"


Database management in GRASS GIS,
Help pages for database modules,
SQL Guide and Reference (Red Hat)

Last changed: $Date: 2008-02-23 19:23:32 -0800 (Sat, 23 Feb 2008) $

Help Index

© 2008 GRASS Development Team