Update existing row in database from pandas df

Question

I have a PostgreSQL db. Pandas has a 'to_sql' function to write the records of a dataframe into a database. But I haven't found any documentation on how to update an existing database row using pandas when im finished with the dataframe.

Currently I am able to read a database table into a dataframe using pandas read_sql_table. I then work with the data as necessary. However I haven't been able to figure out how to write that dataframe back into the database to update the original rows.

I dont want to have to overwrite the whole table. I just need to update the rows that were originally selected.

Answer 1

One way is to make use of an sqlalchemy "table class" and session.merge(row), session.commit():

Here is an example:

for row in range(0, len(df)):     row_data = table_class(column_1=df.ix[i]['column_name'],                            column_2=df.ix[i]['column_name'],                            ...                            )     session.merge(row_data)     session.commit()