drop alter statement to adhere to rule of never writing to source

duckreg/estimators.py

@@ -439,27 +439,26 @@ def __init__(
 
     def prepare_data(self):
         #   create_cohort_and_ever_treated_columns
-        self.cohort_query = f"""
-            ALTER TABLE {self.table_name} ADD COLUMN cohort INTEGER;
-            UPDATE {self.table_name} SET cohort = (
+        self.temp_table_query = f"""
+            CREATE TEMP TABLE temp_{self.table_name} AS
+            SELECT *, NULL::INTEGER AS cohort, NULL::INTEGER AS ever_treated
+            FROM {self.table_name};
+            UPDATE temp_{self.table_name} SET cohort = (
                 SELECT MIN({self.time_col})
                 FROM {self.table_name} AS p2
-                WHERE p2.{self.unit_col} = {self.table_name}.{self.unit_col} AND p2.{self.treatment_col} = 1
+                WHERE p2.{self.unit_col} = temp_{self.table_name}.{self.unit_col} AND
+                p2.{self.treatment_col} = 1
             );
+            UPDATE temp_{self.table_name} SET cohort = NULL WHERE cohort = 2147483647;
+            UPDATE temp_{self.table_name} SET ever_treated = CASE WHEN cohort IS NOT NULL THEN 1 ELSE 0 END;
         """
-        self.conn.execute(self.cohort_query)
-        self.ever_treated_query = f"""
-            UPDATE {self.table_name} SET cohort = NULL WHERE cohort = 2147483647;  -- Set to NULL if never treated
-            ALTER TABLE {self.table_name} ADD COLUMN ever_treated INTEGER;
-            UPDATE {self.table_name} SET ever_treated = CASE WHEN cohort IS NOT NULL THEN 1 ELSE 0 END;
-        """
-        self.conn.execute(self.ever_treated_query)
+        self.conn.execute(self.temp_table_query)
         #  retrieve_num_periods_and_cohorts
         self.num_periods = self.conn.execute(
-            f"SELECT MAX({self.time_col}) FROM {self.table_name}"
+            f"SELECT MAX({self.time_col}) FROM temp_{self.table_name}"
         ).fetchone()[0]
         cohorts = self.conn.execute(
-            f"SELECT DISTINCT cohort FROM {self.table_name} WHERE cohort IS NOT NULL"
+            f"SELECT DISTINCT cohort FROM temp_{self.table_name} WHERE cohort IS NOT NULL"
         ).fetchall()
         self.cohorts = [row[0] for row in cohorts]
         # generate_time_dummies
@@ -506,7 +505,7 @@ def prepare_data(self):
             -- Treated group interacted with treatment time dummies
             {self.treatment_dummies}
         FROM
-            {self.table_name} p;
+            temp_{self.table_name} p;
         """
         self.conn.execute(self.design_matrix_query)