Database: regional_sales
Question: Please indicate store id in the state of California that have been applied 20% discount in store.
SQL: SELECT T FROM ( SELECT DISTINCT CASE  WHEN T2.State = 'California' AND T1.`Sales Channel` = 'In-Store' AND T1.`Discount Applied` = 0.2 THEN T2.StoreID END AS T FROM `Sales Orders` T1 INNER JOIN `Store Locations` T2 ON T2.StoreID = T1._StoreID ) WHERE T IS NOT NULL