v.db.update(1grass) GRASS GIS User's Manual v.db.update(1grass)
NAME
v.db.update - Updates a column in the attribute table connected to a
vector map.
KEYWORDS
vector, attribute table, database, attribute update, type casting
SYNOPSIS
v.db.update
v.db.update --help
v.db.update map=name layer=string column=name [value=string]
[query_column=name] [where=sql_query] [sqliteextra=name] [--help]
[--verbose] [--quiet] [--ui]
Flags:
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
map=name [required]
Name of vector map
Or data source for direct OGR access
layer=string [required]
Layer number or name
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 1
column=name [required]
Name of attribute column to update
value=string
Literal value to update the column with
query_column=name
Name of other attribute column to query, can be combination of col-
umns (e.g. co1+col2)
where=sql_query
WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and population >= 10000
sqliteextra=name
Name of SQLite extension file for extra functions (SQLite backend
only)
DESCRIPTION
v.db.update assigns a new value to a column in the attribute table con-
nected to a given map. The value parameter allows updating with a lit-
eral value. Alternatively, with the qcol parameter values can be copied
from another column in the table or be the result of a combination or
transformation of other columns.
NOTES
v.db.update is just a front-end to db.execute to allow easier usage.
For complex SQL UPDATE statements, db.execute should be used.
EXAMPLES
Replacing of NULL values
In this example, selectively display lakes without (blue) and with NULL
(red) are shown to find out which type is undefined. In the original
map there are lakes missing FTYPE attribute which are wetlands along
streams. These NULL attributes are replaced with the landuse type WET-
LAND:
g.copy vect=lakes,mylakes
v.db.select mylakes
v.db.select mylakes where="FTYPE IS NULL"
# display the lakes, show undefined FTYPE lakes in red
g.region vector=mylakes
d.mon wx0
d.vect mylakes where="FTYPE NOT NULL" type=area col=blue
d.vect mylakes where="FTYPE IS NULL" type=area col=red
# replace NULL with FTYPE WETLAND
v.db.update mylakes col=FTYPE value=WETLAND \
where="FTYPE IS NULL"
v.db.select mylakes
Updating of columns with on the fly calculation
Spearfish example: adding new column, copying values from another table
column with on the fly calculation:
g.copy vect=fields,myfields
v.db.addcolumn myfields col="polynum integer"
v.db.update myfields col=polynum qcol="cat*2"
v.db.select myfields
Type casting
Type cast (type conversion) of strings to double precision (unsupported
by DBF driver):
g.copy vect=geodetic_pts,mygeodetic_pts
v.db.update mygeodetic_pts col=zval qcol="CAST(z_value AS double precision)" \
where="z_value <> ’N/A’"
Updating of columns with on the fly calculation (SQLite extended functions)
Note: this requires SQLite extended functions. For details see the
GRASS GIS Wiki (compilation of libsqlitefunctions.so and libsqlitefunc-
tions.dll).
North Carolina data set example: adding new column, copying values from
another table column with on the fly calculation:
g.copy vect=precip_30ynormals,myprecip_30ynormals
v.db.addcolumn myprecip_30ynormals column="logjuly double precision"
v.db.update myprecip_30ynormals column="logjuly" query_column="log(jul)" \
sqliteextra=$HOME/sqlite_extensions/libsqlitefunctions.so
v.db.select myprecip_30ynormals columns=jul,logjuly
jul|logjuly
132.842|4.88916045210132
127|4.84418708645859
124.206|4.82194147751127
104.648|4.65060233738593
98.298|4.58800368106618
...
SEE ALSO
db.execute, v.db.addcolumn, v.db.addtable, v.db.connect, v.db.dropt-
able, v.db.join, v.db.select
GRASS SQL interface
AUTHOR
Moritz Lennert (mlennert@club.worldonline.be)
SOURCE CODE
Available at: v.db.update source code (history)
Accessed: unknown
Main index | Vector index | Topics index | Keywords index | Graphical
index | Full index
© 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual
GRASS 7.8.7 v.db.update(1grass)
Generated by dwww version 1.14 on Mon Feb 3 07:50:57 CET 2025.