code: def test_sql_join_left() -> None:
      frames = {
          "tbl_a": pl.DataFrame({"a": [1, 2, 3], "b": [4, None, 6]}),
          "tbl_b": pl.DataFrame(
              {"a": [3, 2, 1], "b": [6, 5, 4], "c": ["x", "y", "z"]}
          ),
          "tbl_c": pl.DataFrame(
              {"c": ["w", "y", "z"], "d": [10.5, -50.0, 25.5]}
          ),
      }
      ctx = pl.SQLContext(frames)
      out = ctx.execute(
          """
          SELECT a, b, c, d
          FROM tbl_a
          LEFT JOIN tbl_b USING (a,b)
          LEFT JOIN tbl_c USING (c)
          ORDER BY a DESC
          """
      )
      assert out.collect().rows() == [
          (3, 6, "x", None),
          (2, None, None, None),
          (1, 4, "z", 25.5),
      ]
      assert ctx.tables() == ["tbl_a", "tbl_b", "tbl_c"]
  
imports: from __future__ import annotations
  import datetime
  import math
  from pathlib import Path
  import pytest
  import polars
  import polars.selectors
  from polars.exceptions import ComputeError, InvalidOperationError
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 15 for calling a global function with example usage: test_sql_join_left() without return types