feat: join (#870)

Closes #745 

### Summary of Changes

Implemented a join function for Table

<!-- Please provide a summary of changes in this pull request, ensuring
all changes are explained. -->

---------

Co-authored-by: grefrathc <[email protected]>
Co-authored-by: megalinter-bot <[email protected]>
Co-authored-by: Lars Reimann <[email protected]>

Author: 4 people

src/safeds/data/tabular/containers/_table.py

@@ -1708,6 +1708,65 @@ def inverse_transform_table(self, fitted_transformer: InvertibleTableTransformer
         """
         return fitted_transformer.inverse_transform(self)
 
+    def join(
+        self,
+        right_table: Table,
+        left_names: str | list[str],
+        right_names: str | list[str],
+        *,
+        mode: Literal["inner", "left", "outer"] = "inner",
+    ) -> Table:
+        """
+        Join a table with the current table and return the result.
+
+        Parameters
+        ----------
+        right_table:
+            The other table which is to be joined to the current table.
+        left_names:
+            Name or list of names of columns from the current table on which to join right_table.
+        right_names:
+            Name or list of names of columns from right_table on which to join the current table.
+        mode:
+            Specify which type of join you want to use. Options include 'inner', 'outer', 'left', 'right'.
+
+        Returns
+        -------
+        new_table:
+            The table with the joined table.
+
+        Examples
+        --------
+        >>> from safeds.data.tabular.containers import Table
+        >>> table1 = Table({"a": [1, 2], "b": [3, 4]})
+        >>> table2 = Table({"d": [1, 5], "e": [5, 6]})
+        >>> table1.join(table2, "a", "d", mode="left")
+        +-----+-----+------+
+        |   a |   b |    e |
+        | --- | --- |  --- |
+        | i64 | i64 |  i64 |
+        +==================+
+        |   1 |   3 |    5 |
+        |   2 |   4 | null |
+        +-----+-----+------+
+        """
+        # Validation
+        _check_columns_exist(self, left_names)
+        _check_columns_exist(right_table, right_names)
+
+        if len(left_names) != len(right_names):
+            raise ValueError("The number of columns to join on must be the same in both tables.")
+
+        # Implementation
+        return self._from_polars_lazy_frame(
+            self._lazy_frame.join(
+                right_table._lazy_frame,
+                left_on=left_names,
+                right_on=right_names,
+                how=mode,
+            ),
+        )
+
     def transform_table(self, fitted_transformer: TableTransformer) -> Table:
         """
         Return a new table transformed by a **fitted** transformer.

tests/safeds/data/tabular/containers/_table/test_join.py

@@ -0,0 +1,91 @@
+from typing import Literal
+
+import pytest
+from safeds.data.tabular.containers import Table
+from safeds.exceptions import ColumnNotFoundError
+
+
+@pytest.mark.parametrize(
+    ("table_left", "table_right", "left_names", "right_names", "mode", "table_expected"),
+    [
+        (
+            Table({"a": [1, 2], "b": [3, 4]}),
+            Table({"d": [1, 5], "e": [5, 6]}),
+            ["a"],
+            ["d"],
+            "outer",
+            Table({"a": [1, None, 2], "b": [3, None, 4], "d": [1, 5, None], "e": [5, 6, None]}),
+        ),
+        (
+            Table({"a": [1, 2], "b": [3, 4]}),
+            Table({"d": [1, 5], "e": [5, 6]}),
+            ["a"],
+            ["d"],
+            "left",
+            Table({"a": [1, 2], "b": [3, 4], "e": [5, None]}),
+        ),
+        (
+            Table({"a": [1, 2], "b": [3, 4]}),
+            Table({"d": [1, 5], "e": [5, 6]}),
+            ["a"],
+            ["d"],
+            "inner",
+            Table({"a": [1], "b": [3], "e": [5]}),
+        ),
+        (
+            Table({"a": [1, 2], "b": [3, 4], "c": [5, 6]}),
+            Table({"d": [1, 5], "e": [5, 6], "g": [7, 9]}),
+            ["a", "c"],
+            ["d", "e"],
+            "inner",
+            Table({"a": [1], "b": [3], "c": [5], "g": [7]}),
+        ),
+        (
+            Table({"a": [1, 2], "b": [3, 4]}),
+            Table({"d": [1, 5], "e": [5, 6]}),
+            ["b"],
+            ["e"],
+            "inner",
+            Table({"a": [], "b": [], "d": []}),
+        ),
+    ],
+)
+def test_should_join_two_tables(
+    table_left: Table,
+    table_right: Table,
+    left_names: list[str],
+    right_names: list[str],
+    mode: Literal["inner", "left", "outer"],
+    table_expected: Table,
+) -> None:
+    assert table_left.join(table_right, left_names, right_names, mode=mode) == table_expected
+
+
+def test_should_raise_if_columns_are_mismatched() -> None:
+    table_left = Table({"a": [1, 2], "b": [3, 4]})
+    table_right = Table({"d": [1, 5], "e": [5, 6]})
+    left_names = ["a"]
+    right_names = ["d", "e"]
+    with pytest.raises(ValueError, match="The number of columns to join on must be the same in both tables."):
+        table_left.join(table_right, left_names, right_names)
+
+
+@pytest.mark.parametrize(
+    ("table_left", "table_right", "left_names", "right_names"),
+    [
+        (Table({"a": [1, 2], "b": [3, 4]}), Table({"d": [1, 5], "e": [5, 6]}), ["c"], ["d"]),
+        (Table({"a": [1, 2], "b": [3, 4]}), Table({"d": [1, 5], "e": [5, 6]}), ["a"], ["f"]),
+    ],
+    ids=[
+        "wrong_left_name",
+        "wrong_right_name",
+    ],
+)
+def test_should_raise_if_columns_are_missing(
+    table_left: Table,
+    table_right: Table,
+    left_names: list[str],
+    right_names: list[str],
+) -> None:
+    with pytest.raises(ColumnNotFoundError):
+        table_left.join(table_right, left_names=left_names, right_names=right_names)