GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages
v.db.update(1) Grass User's Manual v.db.update(1)

v.db.update - Updates a column in the attribute table connected to a vector map.

vector, attribute table, database

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]

--help
 
Print usage summary
--verbose
 
Verbose module output
--quiet
 
Quiet module output
--ui
 
Force launching GUI dialog

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 access 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 columns (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)

v.db.update assigns a new value to a column in the attribute table connected to a given map. The value parameter allows updating with a literal 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.

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.

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 WETLAND:
 
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

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 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’"

Note: this requires SQLite extended functions. For details see the GRASS GIS Wiki (compilation of libsqlitefunctions.so and libsqlitefunctions.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
...

db.execute, v.db.addcolumn, v.db.addtable, v.db.connect, v.db.droptable, v.db.join, v.db.select
 
GRASS SQL interface

Moritz Lennert (mlennert@club.worldonline.be)
Last changed: $Date: 2017-03-12 11:58:07 +0100 (Sun, 12 Mar 2017) $

Available at: v.db.update source code (history)
Main index | Vector index | Topics index | Keywords index | Graphical index | Full index
© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference Manual
GRASS 7.4.3

Search for    or go to Top of page |  Section 1 |  Main Index

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with ManDoc.