BUG: Fix if_exists='replace' functionality in io.sql.write_frame

This should resolve issues pandas-dev#2971 and pandas-dev#4110

pandas/io/sql.py

@@ -207,13 +207,13 @@ def write_frame(frame, name, con, flavor='sqlite', if_exists='fail', **kwargs):
     #create or drop-recreate if necessary
     create = None
     if exists and if_exists == 'replace':
-        create = "DROP TABLE %s" % name
+        create = "DROP TABLE %s;" % name + get_schema(frame, name, flavor)
     elif not exists:
         create = get_schema(frame, name, flavor)
 
     if create is not None:
         cur = con.cursor()
-        cur.execute(create)
+        cur.executescript(create)
         cur.close()
 
     cur = con.cursor()

pandas/io/tests/test_sql.py

@@ -244,6 +244,7 @@ def test_if_exists(self):
         df_if_exists_1 = DataFrame({'col1': [1, 2], 'col2': ['A', 'B']})
         df_if_exists_2 = DataFrame({'col1': [3, 4, 5], 'col2': ['C', 'D', 'E']})
         table_name = 'table_if_exists'
+        sql_select = "SELECT * FROM %s" % table_name
 
         # test if invalid value for if_exists raises appropriate error
         self.assertRaises(ValueError,
@@ -258,6 +259,19 @@ def test_if_exists(self):
             cur.execute("DROP TABLE %s" % table_name)
             cur.close()
 
+        # test if_exists='replace'
+        sql.write_frame(frame=df_if_exists_1, con=self.db, name=table_name,
+                        flavor='sqlite', if_exists='replace')
+        sql.write_frame(frame=df_if_exists_2, con=self.db, name=table_name,
+                        flavor='sqlite', if_exists='replace')
+        self.assertEqual(sql.tquery(sql_select, con=self.db),
+                         [(3, 'C'), (4, 'D'), (5, 'E')])
+        if sql.table_exists(table_name, self.db, flavor='sqlite'):
+            cur = self.db.cursor()
+            cur.execute("DROP TABLE %s" % table_name)
+            cur.close()
+
+
 
 class TestMySQL(unittest.TestCase):