v.db.join(1)

NAME
v.db.join - Joins a database table to a vector map table.

KEYWORDS
vector, attribute table, database

SYNOPSIS
v.db.join
v.db.join --help
v.db.join map=name [layer=string] column=name other_table=name other_column=name [subset_columns=name[,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
    Vector map to which to join other table

layer=string
    Layer number or name
    Layer where to join
    Default: 1

column=name [required]
    Identifier column (e.g.: cat) in the vector table to be used for join

other_table=name [required]
    Other table name

other_column=name [required]
    Identifier column (e.g.: id) in the other table used for join

subset_columns=name[,name,...]
    Subset of columns from the other table

DESCRIPTION
v.db.join joins the content of another table into the connected attribute table of a vector map.

NOTES
v.db.join is a front-end to db.execute to allow easier usage. The vector attribute table must be stored in a SQL database (SQLite, PostgreSQL, MySQL, ODBC, ...). The DBF backend is not supported. Tables can be imported with db.in.ogr.

The vector map-database connection(s) can be verified with v.db.connect.

EXAMPLES
Exercise to join North Carolina geological classes from a CSV table to the "geology" map of the North Carolina sample dataset (requires download of legend CSV file nc_geology.csv from External data for NC sample dataset):

# check original map attributes
v.db.select geology column=GEO_NAME,SHAPE_area
# import of CSV table
db.in.ogr input=nc_geology.csv output=nc_geology
# work on copy of geology map in current mapset
g.copy vector=geology,mygeology
# check column names of vector map attributes
v.info -c mygeology
# check column names of legend table
db.describe -c nc_geology
# join table using key columns (map: "GEO_NAME"; table: "geol_id")
v.db.join map=mygeology column=GEO_NAME other_table=nc_geology other_column=geol_id
# verify result (here abbreviated)
v.db.select mygeology | head -3
cat|onemap_pro|PERIMETER|GEOL250_|GEOL250_ID|GEO_NAME|SHAPE_area|SHAPE_len|geol_id|longname|comment
1|963738.75|4083.97998|2|1|Zml|963738.608571|4083.979839|Zml|Metagraywacke|Interlayered with metaconglomerate, ...
2|22189124|26628.261719|3|2|Zmf|22189123.2296|26628.261112|Zmf|Metafelsite|Light-colored porphyritic extrusive rock
...

  Soil map table join
Joining the soil type explanations from table soils_legend into the Spearfish soils map (download legend):

g.copy vect=soils,mysoils
# import legend table
db.in.ogr soils_legend.csv out=soils_legend
# get join column names
v.info -c mysoils
db.describe -c soils_legend
# look at original table
v.db.select mysoils
cat|label
1|Aab
2|Ba
3|Bb
4|BcB
5|BcC
...
# look at legend
db.select table=soils_legend
db.select table=soils_legend | head -7
id|shortname|longname
0|no data|no data
0|AaB|Alice fine sandy loam, 0 to 6
0|Ba|Barnum silt loam
0|Bb|Barnum silt loam, channeled
0|BcB|Boneek silt loam, 2 to 6
0|BcC|Boneek silt loam, 6 to 9
...
# join soils_legend into mysoils attribute table
v.db.join mysoils col=label other_table=soils_legend ocol=shortname
# verification of join
v.db.select mysoils
cat|label|id|shortname|longname
1|Aab|||
2|Ba|2|Ba|Barnum silt loam
3|Bb|3|Bb|Barnum silt loam, channeled
4|BcB|4|BcB|Boneek silt loam, 2 to 6
5|BcC|5|BcC|Boneek silt loam, 6 to 9
...

SEE ALSO
db.execute, db.in.ogr, db.select, v.db.update
GRASS SQL interface

AUTHOR
Markus Neteler

SOURCE CODE

Available at: v.db.join source code (history)

Accessed: Wednesday Jul 09 13:14:36 2025

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