NAME¶

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

KEYWORDS¶

vector, database, attribute table

SYNOPSIS¶

v.db.update v.db.update help v.db.update map=string [layer=string] column=string [value=string] [qcolumn=string] [ where=string] [--verbose] [-- quiet]

Parameters:¶

map=string

 

Vector map to edit the attribute table for

layer=string

 

Layer to which the table to be changed is connected

 

Default: 1

column=string

 

Column to update

value=string

 

Value to update the column with (varchar values have to be in single quotes, e.g. 'grass')

qcolumn=string

 

Column to query

where=string

 

WHERE conditions for update, without 'where' keyword (e.g. cat=1 or col1/col2>1)

DESCRIPTION¶

v.db.update allows to assign a new value to a column in the attribute table connected to a given map. Alternatively, values can be copied from another column in the table.

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¶

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 vect=mylakes d.mon x0 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 other table column with on the fly calculation: g.copy vect=fields,myfields v.db.addcol 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'"

SEE ALSO¶

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

AUTHOR¶

Moritz Lennert (mlennert@club.worldonline.be) Last changed: $Date: 2011-11-22 23:29:56 +0100 (Tue, 22 Nov 2011) $ Full index © 2003-2011 GRASS Development Team