feat: Initial support for SQL ARRAY literals and the UNNEST table function

[alexander-beedie]

Update

Started extending our SQL interface support to list/array data:

• Can now use SQL ARRAY literals and declare UNNEST table functions.
• Can write array literals as either [1,2,3] or ARRAY[1,2,3].
• Cast with col::type[] or CAST(col AS type[]) syntax.

Examples

import polars as pl

with pl.SQLContext(df=None) as sql:
    df1 = sql.execute(
        """
        SELECT 
          ['x','y'] AS a1,
          [3,4,5,6,7,8]::float4[] AS a2 
        FROM df
        """
    ).collect()
    
    # shape: (1, 2)
    # ┌────────────┬───────────────────┐
    # │ a1         ┆ a2                │
    # │ ---        ┆ ---               │
    # │ list[str]  ┆ list[f32]         │
    # ╞════════════╪═══════════════════╡
    # │ ["x", "y"] ┆ [3.0, 4.0, … 8.0] │
    # └────────────┴───────────────────┘

    df2 = sql.execute(
        """
        SELECT * FROM
          UNNEST(
            [10, 20, 30, 40],
            ['ww','xx','yy','zz'],
            [23.0, 24.5, 28.0, 27.5]
          ) AS tbl (x,y,z)
        """
    ).collect()

    # shape: (4, 3)
    # ┌─────┬─────┬──────┐
    # │ x   ┆ y   ┆ z    │
    # │ --- ┆ --- ┆ ---  │
    # │ i64 ┆ str ┆ f64  │
    # ╞═════╪═════╪══════╡
    # │ 10  ┆ ww  ┆ 23.0 │
    # │ 20  ┆ xx  ┆ 24.5 │
    # │ 30  ┆ yy  ┆ 28.0 │
    # │ 40  ┆ zz  ┆ 27.5 │
    # └─────┴─────┴──────┘

Follow-ups

• Contribute a PR to sqlparser-rs to support UNNEST ... WITH ORDINALITY.
• Support nested array literals (eg: [[1,2,3], [4,5,6]]).

[codecov]

Codecov Report

Attention: Patch coverage is 94.68085% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 81.50%. Comparing base (b85c5e0) to head (008e0fb).
Report is 2 commits behind head on main.

Files	Patch %	Lines
crates/polars-sql/src/sql_expr.rs	94.11%	3 Missing ⚠️
crates/polars-sql/src/context.rs	95.34%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16330      +/-   ##
==========================================
- Coverage   81.51%   81.50%   -0.01%     
==========================================
  Files        1414     1414              
  Lines      185944   185997      +53     
  Branches     3027     3027              
==========================================
+ Hits       151569   151606      +37     
- Misses      33844    33861      +17     
+ Partials      531      530       -1     

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[codspeed-hq]

CodSpeed Performance Report

Merging #16330 will improve performances by 19.76%

_{Comparing alexander-beedie:sql-array-literal (008e0fb) with main (b85c5e0)}

Summary

⚡ 1 improvements
✅ 36 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	alexander-beedie:sql-array-literal	Change
⚡	test_tpch_q22	6.3 ms	5.3 ms	+19.76%