## 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

Last changed: $Date: 2015-12-17 15:38:13 +0100 (Thu, 17 Dec 2015) $