How to insert a pandas dataframe to an already existing table in a database?
<p>I'm using <code>sqlalchemy</code> in pandas to query postgres database and then insert results of a transformation to another table on the same database. But when I do 
<code>df.to_sql('db_table2', engine)</code> I get this error message:
<code>ValueError: Table 'db_table2' already exists.</code> I noticed it want to create a new table. How to insert pandas dataframe to an already existing table ? </p>

<pre><code>df = pd.read_sql_query('select * from "db_table1"',con=engine)
#do transformation then save df to db_table2
df.to_sql('db_table2', engine)

ValueError: Table 'db_table2' already exists
</code></pre>