On Jan 24, 2012, at 1:29 PM, Moritz Lennert wrote: > On 24/01/12 19:49, Kirk Wythers wrote: >> I am trying to do a 'join' of a column from one table, to the attribute >> table of another vector. However, I am getting an error about a problem >> adding another column due to a duplicate column name. >> >> Snip of commands are below: >> >> GRASS 6.4.1 (latlon):~> v.info -c ew4kmg >> Displaying column types/names for database connection of layer 1: >> INTEGER|cat >> INTEGER|Id >> DOUBLE PRECISION|XMIN >> DOUBLE PRECISION|XMAX >> DOUBLE PRECISION|YMIN >> DOUBLE PRECISION|YMAX >> >> GRASS 6.4.1 (latlon):~> db.describe -c ew4km_tawc >> ncols: 13 >> nrows: 265090 >> Column 1: ID:INTEGER:20 >> Column 2: COUNT:INTEGER:20 >> Column 3: AREA:DOUBLE PRECISION:20 >> Column 4: MIN:INTEGER:20 >> Column 5: MAX:INTEGER:20 >> Column 6: RANGE:INTEGER:20 >> Column 7: MEAN:DOUBLE PRECISION:20 >> Column 8: STD:DOUBLE PRECISION:20 >> Column 9: SUM:DOUBLE PRECISION:20 >> Column 10: VARIETY:INTEGER:20 >> Column 11: MAJORITY:INTEGER:20 >> Column 12: MINORITY:INTEGER:20 >> Column 13: MEDIAN:INTEGER:20 >> >> GRASS 6.4.1 (latlon):~> v.db.select ew4kmg | head -7 >> cat|Id|XMIN|XMAX|YMIN|YMAX >> 1|128|-1793092|-1789092|-1142894|-1138894 >> 2|129|-1793092|-1789092|-1138894|-1134894 >> 3|130|-1793092|-1789092|-1134894|-1130894 >> 4|826|-1789092|-1785092|-1150894|-1146894 >> 5|827|-1789092|-1785092|-1146894|-1142894 >> 6|828|-1789092|-1785092|-1142894|-1138894 >> >> GRASS 6.4.1 (latlon):~> db.select ew4km_tawc | head -7 >> ID|COUNT|AREA|MIN|MAX|RANGE|MEAN|STD|SUM|VARIETY|MAJORITY|MINORITY|MEDIAN >> 127|349|314100|2163|2850|687|2199.68|131.842|767687|36|2163|2185|2163 >> 128|7906|7115400|932|2850|1918|2182.34|534.089|17253600|252|2762|1245|2202 >> 129|10528|9475200|864|2762|1898|1733.46|877.929|18249900|3|864|1568|1568 >> 130|15421|13878900|539|2850|2311|1403.27|806.156|21639900|80|864|539|864 >> 131|17822|16039800|864|2762|1898|1024.77|111.876|18263400|3|1096|2762|1096 >> 132|17689|15920100|864|1096|232|1076.65|64.1395|19044900|2|1096|864|1096 >> >> So I am trying to perform the join the MEAN column in the table ew4km_tawc >> on the Id column in the map ew4kmg. Here is the output: >> >> GRASS 6.4.1 (latlon):~> v.db.join map=ew4kmg column=Id otable=ew4km_tawc >> ocolumn=MEAN >> DBMI-SQLite driver error: >> Error in sqlite3_prepare(): >> duplicate column name: ID >> >> ERROR: Error while executing: 'ALTER TABLE ew4kmg ADD COLUMN ID INTEGER >> ' >> ERROR: Cannot continue (problem adding column). >> ERROR: Cannot continue. >> >> I am confused since it seems to me, that there has to be a duplicate column >> name (in this case 'ID', in order for the join to know what to join on… Any >> suggestions would be much appreciated! > > No, there has to be two columns containing the join criterium, but these do > not have to have the same column name. As you can see from the error, they > actually shouldn't have the same name (note: the module should probably just > prefix each column with the name of the original table to avoid such > issues...but then you run into column name length issues.). > > You v.db.join is incorrect as well, as your ocolumn is ID, not MEAN. the > column and ocolumn options designate the respective columns in the two tables > that contain the join criterium. All of the other columns of otable will be > joined to the table of your vector map. >
Thanks Moritz, I just want to make sure I understand your point… I want to attach the "MEAN" from the table "ew4km_tawc" added to the vector map "ew4kmg" where ew4kmg_Id is the same as ew4km_tawc_ID, so you are saying that my join needs to be: v.db.join ew4kmg col=Id otable=ew4km_tawc ocol=ID?
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