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 soils_legend
db.select 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 otable=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
...

# join soils_legend into mysoils attribute table, escape shortname column that it is a duplicate of label; it add also _o suffix for the columns contained by soils_legend table
g.copy vect=soils,mysoils_ac
v.db.join -ac mysoils col=label otable=soils_legend ocol=shortname

# verification of join
v.db.select mysoils_ac
cat|label|id|longname_o
1|Aab|||
2|Ba|2|Barnum silt loam
3|Bb|3|Barnum silt loam, channeled
4|BcB|4|Boneek silt loam, 2 to 6
5|BcC|5|Boneek silt loam, 6 to 9