Geografic-Information-System/scripts/v.db.join/v.db.join.html

<h2>DESCRIPTION</h2>

<em>v.db.join</em> joins the content of another table into the connected
attribute table of a vector map.

<h2>NOTES</h2>

<em>v.db.join</em> is a front-end to <em>db.execute</em> 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 <em>db.in.ogr</em>.
<p>The vector map-database connection(s) can be verified with <em>v.db.connect</em>.

<h2>EXAMPLES</h2>

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 <a href="http://www.grassbook.org/wp-content/uploads/ncexternal/nc_geology.csv">nc_geology.csv</a>
from <a href="http://www.grassbook.org/wp-content/uploads/ncexternal/index.html">External data for NC sample dataset</a>):

<div class="code"><pre>
# 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
...
</pre></div>


<h3>Soil map table join</h3>

Joining the soil type explanations from table <em>soils_legend</em>
into the Spearfish soils map (<a href="http://www.grassbook.org/code-examples/code-examples-1st-edition/">download legend</a>):

<div class="code"><pre>
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
...
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="db.execute.html">db.execute</a>,
<a href="db.in.ogr.html">db.in.ogr</a>,
<a href="db.select.html">db.select</a>,
<a href="v.db.update.html">v.db.update</a><br>
<a href="sql.html">GRASS SQL interface</a>
</em>

<h2>AUTHOR</h2>

Markus Neteler

<p><i>Last changed: $Date$</i>