API to_sql method doesn't provide the option to specify unique indexes
This could very well be something that just isn't clear to me from reading the docs, but I would like to have my index be unique when I dump the dataframe to SQLite table so that when I append more data I don't get duplicate rows. Here's what my resulting scheme looks like after using the to_sql function

sqlite> .schema
CREATE TABLE "Sniffs" (
    "ID" TEXT, 
    "Day" TEXT, 
    "ModelName" TEXT, 
    "PassRate" FLOAT, 
    "RtxName" TEXT, 
    "Shadow" TEXT, 
    "Time" TEXT, 
    "Unit" TEXT
);
CREATE INDEX "ix_Sniffs_ID" ON "Sniffs" ("ID");

Looking at these docs:
http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_sql.html#pandas.DataFrame.to_sql

My resulting call looks something like this:
sniff_df.to_sql('Sniffs', sqleng, if_exists='append', index_label='ID')

Am I reading the docs wrong or anything/is there currently a method to get unique indexes in the output sql to avoid overlapping data? Could we get a kwarg like: unique_index=True ?
