Truncate table option for to sql

doc/source/whatsnew/v1.5.3.rst

@@ -32,7 +32,7 @@ Bug fixes
 
 Other
 ~~~~~
--
+- 
 -
 
 .. ---------------------------------------------------------------------------

doc/source/whatsnew/v2.0.0.rst

@@ -83,7 +83,7 @@ Other enhancements
 - :func:`timedelta_range` now supports a ``unit`` keyword ("s", "ms", "us", or "ns") to specify the desired resolution of the output index (:issue:`49824`)
 - :meth:`DataFrame.to_json` now supports a ``mode`` keyword with supported inputs 'w' and 'a'. Defaulting to 'w', 'a' can be used when lines=True and orient='records' to append record oriented json lines to an existing json file. (:issue:`35849`)
 - Added ``name`` parameter to :meth:`IntervalIndex.from_breaks`, :meth:`IntervalIndex.from_arrays` and :meth:`IntervalIndex.from_tuples` (:issue:`48911`)
--
+- Added ``"truncate"`` option to ``if_exists`` argument in :meth:`DataFrame.to_sql` to truncate the existing table (:issue:`37210`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_200.notable_bug_fixes:

pandas/io/sql.py

@@ -604,7 +604,7 @@ def to_sql(
     name: str,
     con,
     schema: str | None = None,
-    if_exists: Literal["fail", "replace", "append"] = "fail",
+    if_exists: Literal["fail", "replace", "append", "truncate"] = "fail",
     index: bool = True,
     index_label: IndexLabel = None,
     chunksize: int | None = None,
@@ -629,10 +629,11 @@ def to_sql(
     schema : str, optional
         Name of SQL schema in database to write to (if database flavor
         supports this). If None, use default schema (default).
-    if_exists : {'fail', 'replace', 'append'}, default 'fail'
+    if_exists : {'fail', 'replace', 'append', 'truncate}, default 'fail'
         - fail: If table exists, do nothing.
         - replace: If table exists, drop it, recreate it, and insert data.
         - append: If table exists, insert data. Create if does not exist.
+        - truncate: If table exists, truncate it, then insert data.
     index : bool, default True
         Write DataFrame index as a column.
     index_label : str or sequence, optional
@@ -682,7 +683,7 @@ def to_sql(
     `sqlite3 <https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.rowcount>`__ or
     `SQLAlchemy <https://docs.sqlalchemy.org/en/14/core/connections.html#sqlalchemy.engine.BaseCursorResult.rowcount>`__
     """  # noqa:E501
-    if if_exists not in ("fail", "replace", "append"):
+    if if_exists not in ("fail", "replace", "append", "truncate"):
         raise ValueError(f"'{if_exists}' is not valid for if_exists")
 
     if isinstance(frame, Series):
@@ -854,6 +855,8 @@ def create(self) -> None:
             if self.if_exists == "replace":
                 self.pd_sql.drop_table(self.name, self.schema)
                 self._execute_create()
+            elif self.if_exists == "truncate":
+                self.pd_sql.trunc_table(self.name, self.schema)
             elif self.if_exists == "append":
                 pass
             else:
@@ -1311,7 +1314,7 @@ def to_sql(
         self,
         frame,
         name,
-        if_exists: Literal["fail", "replace", "append"] = "fail",
+        if_exists: Literal["fail", "replace", "append", "truncate"] = "fail",
         index: bool = True,
         index_label=None,
         schema=None,
@@ -1642,7 +1645,7 @@ def prep_table(
         self,
         frame,
         name,
-        if_exists: Literal["fail", "replace", "append"] = "fail",
+        if_exists: Literal["fail", "replace", "append", "truncate"] = "fail",
         index: bool | str | list[str] | None = True,
         index_label=None,
         schema=None,
@@ -1718,7 +1721,7 @@ def to_sql(
         self,
         frame,
         name: str,
-        if_exists: Literal["fail", "replace", "append"] = "fail",
+        if_exists: Literal["fail", "replace", "append", "truncate"] = "fail",
         index: bool = True,
         index_label=None,
         schema: str | None = None,
@@ -1736,10 +1739,11 @@ def to_sql(
         frame : DataFrame
         name : string
             Name of SQL table.
-        if_exists : {'fail', 'replace', 'append'}, default 'fail'
+        if_exists : {'fail', 'replace', 'append', 'truncate'}, default 'fail'
             - fail: If table exists, do nothing.
             - replace: If table exists, drop it, recreate it, and insert data.
             - append: If table exists, insert data. Create if does not exist.
+            - truncate: If table exists, truncate it, and insert data.
         index : boolean, default True
             Write DataFrame index as a column.
         index_label : string or sequence, default None
@@ -1833,6 +1837,13 @@ def drop_table(self, table_name: str, schema: str | None = None) -> None:
             self.get_table(table_name, schema).drop(bind=self.con)
             self.meta.clear()
 
+    def trunc_table(self, table_name: str, schema: str | None = None) -> None:
+        schema = schema or self.meta.schema
+        if self.has_table(table_name, schema):
+            self.meta.reflect(bind=self.con, only=[table_name], schema=schema)
+            self.execute(f"TRUNCATE TABLE {schema}.{table_name}")
+            self.meta.clear()
+
     def _create_sql_schema(
         self,
         frame: DataFrame,
@@ -2181,10 +2192,11 @@ def to_sql(
         frame: DataFrame
         name: string
             Name of SQL table.
-        if_exists: {'fail', 'replace', 'append'}, default 'fail'
+        if_exists: {'fail', 'replace', 'append', 'truncate}, default 'fail'
             fail: If table exists, do nothing.
             replace: If table exists, drop it, recreate it, and insert data.
             append: If table exists, insert data. Create if it does not exist.
+            truncate: If table exists, truncate it, then insert data.
         index : bool, default True
             Write DataFrame index as a column
         index_label : string or sequence, default None
@@ -2253,6 +2265,9 @@ def drop_table(self, name: str, schema: str | None = None) -> None:
         drop_sql = f"DROP TABLE {_get_valid_sqlite_name(name)}"
         self.execute(drop_sql)
 
+    def trunc_table(self, name: str, schema: str | None = None) -> None:
+        raise NotImplementedError("TRUNCATE not implemented on database")
+
     def _create_sql_schema(
         self,
         frame,

pandas/tests/io/test_sql.py

@@ -902,6 +902,36 @@ def test_to_sql_replace(self, test_frame1):
 
         assert num_rows == num_entries
 
+    def test_to_sql_truncate(self, test_frame1):
+        sql.to_sql(test_frame1, "test_frame3", self.conn, if_exists="fail")
+        # Add to table again
+        sql.to_sql(test_frame1, "test_frame3", self.conn, if_exists="truncate")
+        assert sql.has_table("test_frame3", self.conn)
+
+        num_entries = len(test_frame1)
+        num_rows = count_rows(self.conn, "test_frame3")
+
+        assert num_rows == num_entries
+
+    def test_to_sql_truncate_no_table(self, test_frame1):
+        #  creates new table if table doesn't exist
+        sql.to_sql(test_frame1, "test_frame_new", self.conn, if_exists="truncate")
+        assert sql.has_table("test_frame_new")
+
+    def test_to_sql_truncate_new_columns(self, test_frame1, test_frame3):
+        sql.to_sql(test_frame3, "test_frame3", self.conn, if_exists="fail")
+        # truncate and attempt to add more columns
+        msg = "table test_frame3 has no column named C"
+        with pytest.raises(Exception, match=msg):
+            sql.to_sql(test_frame1, "test_frame3", self.conn, if_exists="truncate")
+
+    def test_sqlite_truncate_raises(self, test_frame1):
+        msg = "TRUNCATE not implemented on database"
+        with pytest.raises(NotImplementedError, match=msg):
+            sql.to_sql(
+                test_frame1, "test_frame3", self.conn, if_exists="truncate"
+            )
+
     def test_to_sql_append(self, test_frame1):
         assert sql.to_sql(test_frame1, "test_frame4", self.conn, if_exists="fail") == 4