human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Stellar mass ( M☉ ), Planetary mass ( M⊕ ), Lum. (L 0 ), Type, RHAB ( AU ), RV (cm/s), Period (days)
###Question: What is the smallest period (days) to have a planetary mass of 1, a stellar mass greater than 0.21 and of the type M0?
gpt
SELECT MIN Period (days) FROM table WHERE Planetary mass ( M⊕ ) = 1 AND Stellar mass ( M☉ ) > 0.21 AND Type = m0