Only a column name can be used for the key in a dtype mappings argument

Question

I've successfully brought in one table using dask read_sql_table from a oracle database. However, when I try to bring in another table I get this error KeyError: 'Only a column name can be used for the key in a dtype mappings argument.'

I've checked my connection string and schema and all of that is fine. I know the table name exists and the column i'm trying to use as an index is a primary key on the table in the oracle database.

Can someone please explain why this error occurs when the column name clearly exists?

I know I can use Pandas chunk, but would rather use dask in this scenario.

below is how i'm connecting to the oracle database and the last bit of the error message

host='*******'
port='*****'
sid='****'
user='******'
password='*****'

con_string = 'oracle://' + user + ':' + password + '@' + host + ':' + port + '/' + sid 
engine = create_engine(con_string)

df =ddf.read_sql_table('table_name', uri=con_string, index_col='id', npartitions=None, schema='*****')

~\AppData\Local\Continuum\anaconda3\lib\site-packages\pandas\core\generic.py in astype(self, dtype, copy, errors, **kwargs) 5855
if col_name not in self: 5856 raise KeyError( -> 5857 "Only a column name can be used for the " 5858 "key in a dtype mappings argument." 5859 )

KeyError: 'Only a column name can be used for the key in a dtype mappings argument.'

Today for another table I added all the column names in ddf.read_sql_table and the query worked. But for another table I tried to do the same thing by listing all the column names and I got the KeyError above.

Thanks everyone.

Answer 1

This error generally occurs when there is a mismatch in the column name or there exists a column in the dtype mapping which is not present in the table.