ENH: function for truncating (deleting all rows) an existing table
Hi,
I want to truncate (or even drop) an existing table in SQL server. I didn't find any dedicated function in pandas.io.sql. So I tried to create an empty data frame just to call:

```
df1 = pd.DataFrame()
df1.to_sql(out_tbl, engine, if_exists='replace', index=False)
```

This code does drop the table but then generates exception from sqlalchemy as it tries to re-create an empty table. I can catch and ignore it, and the next call to_sql() with if_exists='append' will create the table correctly, but this is pretty ugly.

Another way I tried is to clear all the rows from the original data frame, leaving the columns:

```
df1 = df.drop(df.index)
df1.to_sql(out_tbl, engine, if_exists='replace', index=False)
```

This almost works: it truncates the table but then insert a single record with all fields as NULL...

You can see the full description at http://stackoverflow.com/questions/26205057/how-can-i-truncate-a-table-using-pandas#comment41130846_26205057
