feat: Support SQL VALUES clause and inline renaming of columns in CTE & derived table definitions

[alexander-beedie]

Adds new SQL interface support for...

• The VALUES¹ clause (doesn't support inline literal casts or typed literals yet).
• Column (re)naming in derived table aliases (eg: CTEs and VALUES clause).

Example

Standalone VALUES clause:

pl.sql("VALUES (1,2), (3,4)").collect()
# shape: (2, 2)
# ┌──────────┬──────────┐
# │ column_0 ┆ column_1 │
# │ ---      ┆ ---      │
# │ i32      ┆ i32      │
# ╞══════════╪══════════╡
# │ 1        ┆ 2        │
# │ 3        ┆ 4        │
# └──────────┴──────────┘

Select from VALUES, applying column names with the table alias:

pl.sql("SELECT * FROM (VALUES(1,2), (3,4)) AS tbl(colx, coly)").collect()
# shape: (2, 2)
# ┌──────┬──────┐
# │ colx ┆ coly │
# │ ---  ┆ ---  │
# │ i32  ┆ i32  │
# ╞══════╪══════╡
# │ 1    ┆ 2    │
# │ 3    ┆ 4    │
# └──────┴──────┘

Demonstrate/stress-test name/alias resolution; select from inner VALUES and show that we successfully map column/table names through multiple levels of nested CTEs and derived table column aliasing.

df = pl.sql(
  """
  WITH
    x AS (SELECT w.* FROM (VALUES(1,2), (3,4)) AS w(a, b)),
    y (m, n) AS (
      WITH z(c, d) AS (SELECT a, b FROM x)
        SELECT d*2 AS d2, c*3 AS c3 FROM z
  )
  SELECT n, m FROM y
  """,
  eager=True,
)
# shape: (2, 2)
# ┌─────┬─────┐
# │ n   ┆ m   │
# │ --- ┆ --- │
# │ i32 ┆ i32 │
# ╞═════╪═════╡
# │ 3   ┆ 4   │
# │ 9   ┆ 8   │
# └─────┴─────┘

Footnotes

1. PostgreSQL VALUES clause: https://www.postgresql.org/docs/current/sql-values.html ↩

[codecov]

Codecov Report

Attention: Patch coverage is 97.56098% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.39%. Comparing base (3a56f09) to head (73a63a3).
Report is 8 commits behind head on main.

Files	Patch %	Lines
crates/polars-sql/src/context.rs	97.56%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16851      +/-   ##
==========================================
- Coverage   81.39%   81.39%   -0.01%     
==========================================
  Files        1425     1425              
  Lines      187627   187701      +74     
  Branches     2702     2702              
==========================================
+ Hits       152727   152784      +57     
- Misses      34404    34421      +17     
  Partials      496      496              

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