title: Using pandas to_sql to append data frame to an existing table in sql server gives IntegrityError
body: <p>I tried to append my pandas dataframe to an existing data table in sql server like below.  All my column names in the data are absolutely identical to the database table. </p>
  
  <pre><code>df.to_sql(table_name,engine,schema_name,index=False,method='multi',if_exists='append',chunksize=100)
  </code></pre>
  
  <p>But it failed and I got error like below:</p>
  
  <pre><code>IntegrityError: ('23000', "[23000] [Microsoft][ODBC Driver 17 for SQL Server]
  [SQL Server]Cannot insert explicit value for identity column in table 'table_name' 
  when IDENTITY_INSERT is set to OFF. (544) (SQLParamData)")
  </code></pre>
  
  <p>I have non clue what that means and what I should do to make it work. It looks like the issue is <code>IDENTITY_INSERT is set to OFF</code>?.  Appreciate if anyone can help me understand why and what potentially I can do. Thanks.</p>