On Thursday, February 14, 2013 4:31 AM Andrew Taylor wrote: > Hi, > I'd like to do something which I think should be quite easy - that is join 2 tables and create a new table.
> Table A postcode_input has columns which include postcode, eastings, northings. there are 1,687,605 rows. > Table B bng_lat_long has columns lat, lon, e, n. There are 1,687,605 rows. > eastings = e and northings = n so there should be a 1 to 1 match. The eastings northings pair should be unique in > aggregate. I think mapping is m to n. >So I tried doing this: > SELECT A.postcode, A.eastings, A.northings, B.lat, B.lon INTO postcode_lat_long > FROM postcode_input AS A > LEFT JOIN bng_lat_long AS B On A.eastings = B.e AND A.northings = B.n > And ended up with a table 13,708,233 rows long with what looks like plenty of duplicated rows. Some but not all are > duplicated. What can I do to sort this out? What is you exact expection of data in postcode_lat_long? From the above it seems you want distinct rows which match between postcode_input and bng_lat_long, if there is no match then take the values of postcode_input and NULL for bng_lat_long. If I am right, then you can try with using DISTINCT operator: http://www.postgresql.org/docs/9.2/static/sql-select.html#SQL-DISTINCT With Regards, Amit Kapila. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
