pythonpython-polarsrust-polars

Polars SQL Context filter by date or datetime


I'm trying to write a query against parquet using Polars SQL Context. It's working great if I pre-filter my arrow table by date. I cannot figure out how to use date in the SQL query.

works:

filters = define_filters(event.get("filters", None))
table = pq.read_table(
    f"s3://my_s3_path{partition_path}",
    partitioning="hive",
    filters=filters,
)
df = pl.from_arrow(table)
ctx = pl.SQLContext(stuff=df)
sql = "SELECT things FROM stuff"
new_df = ctx.execute(sql,eager=True)

doesn't work (filters==None in this case):

filters = define_filters(event.get("filters", None))
table = pq.read_table(
    f"s3://my_s3_path{partition_path}",
    partitioning="hive",
    filters=filters,
)
df = pl.from_arrow(table)
ctx = pl.SQLContext(stuff=df)
sql = """
    SELECT things 
    FROM stuff 
    where START_DATE_KEY >= '2023-06-01' and START_DATE_KEY < '2023-06-17'
"""
new_df = ctx.execute(sql,eager=True)

I get the following error:

Traceback (most recent call last):
  File "/Users/xaras/projects/arrow-lambda/loose.py", line 320, in <module>
    test_runner(target=args.t, limit=args.limit, is_debug=args.debug)
  File "/Users/xaras/projects/arrow-lambda/loose.py", line 294, in test_runner
    rows, metadata = test_handler(target, limit, display=True, is_debug=is_debug)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xaras/projects/arrow-lambda/loose.py", line 110, in test_handler
    response = json.loads(handler(event, None))
                          ^^^^^^^^^^^^^^^^^^^^
  File "/Users/xaras/projects/arrow-lambda/serverless/app.py", line 42, in handler
    new_df = ctx.execute(
             ^^^^^^^^^^^^
  File "/Users/xaras/.pyenv/versions/pyarrow/lib/python3.11/site-packages/polars/sql/context.py", line 275, in execute
    return res.collect() if (eager or self._eager_execution) else res
           ^^^^^^^^^^^^^
  File "/Users/xaras/.pyenv/versions/pyarrow/lib/python3.11/site-packages/polars/utils/deprecation.py", line 95, in wrapper
    return function(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xaras/.pyenv/versions/pyarrow/lib/python3.11/site-packages/polars/lazyframe/frame.py", line 1713, in collect
    return wrap_df(ldf.collect())
                   ^^^^^^^^^^^^^
exceptions.ComputeError: cannot compare 'date/datetime/time' to a string value (create native python { 'date', 'datetime', 'time' } or compare to a temporal column)

UPDATE for addl info:

I started using cast('2023-06-01' as date). This runs, but does not return any records.

Here is a replicatable example:

import polars as pl

df = pl.DataFrame(
    {
        "a": ["2023-06-01", "2023-06-01", "2023-06-02"],
        "b": [None, None, None],
        "c": [4, 5, 6],
        "d": [None, None, None],
    }
)
df = df.with_columns(pl.col("a").str.strptime(pl.Date, "%Y-%m-%d", strict=False))
print(df)
ctx = pl.SQLContext(stuff=df)
new_df = ctx.execute(
    "select * from stuff where a = cast('2023-06-01' as date)",
    eager=True,
)
print(new_df)


## Returns...
shape: (3, 4)
┌────────────┬──────┬─────┬──────┐
│ a          ┆ b    ┆ c   ┆ d    │
│ ---        ┆ ---  ┆ --- ┆ ---  │
│ date       ┆ f32  ┆ i64 ┆ f32  │
╞════════════╪══════╪═════╪══════╡
│ 2023-06-01 ┆ null ┆ 4   ┆ null │
│ 2023-06-01 ┆ null ┆ 5   ┆ null │
│ 2023-06-02 ┆ null ┆ 6   ┆ null │
└────────────┴──────┴─────┴──────┘
shape: (0, 4)
┌──────┬─────┬─────┬─────┐
│ a    ┆ b   ┆ c   ┆ d   │
│ ---  ┆ --- ┆ --- ┆ --- │
│ date ┆ f32 ┆ i64 ┆ f32 │
╞══════╪═════╪═════╪═════╡
└──────┴─────┴─────┴─────┘

Solution

  • DATE() was was added as an SQL function in Polars 0.19.9

    import polars as pl
    
    df = pl.DataFrame(
        {
            "a": ["2023-06-01", "2023-06-01", "2023-06-02"],
            "b": [None, None, None],
            "c": [4, 5, 6],
            "d": [None, None, None],
        }
    )
    
    df = df.with_columns(pl.col("a").str.to_date())
    
    with pl.SQLContext(stuff=df) as ctx:
        ctx.execute(
            "select * from stuff where a = date('2023-06-01')",
            eager=True
        )
    
    shape: (2, 4)
    ┌────────────┬──────┬─────┬──────┐
    │ a          ┆ b    ┆ c   ┆ d    │
    │ ---        ┆ ---  ┆ --- ┆ ---  │
    │ date       ┆ f32  ┆ i64 ┆ f32  │
    ╞════════════╪══════╪═════╪══════╡
    │ 2023-06-01 ┆ null ┆ 4   ┆ null │
    │ 2023-06-01 ┆ null ┆ 5   ┆ null │
    └────────────┴──────┴─────┴──────┘
    

    Being able to use .cast() to go from str -> date|datetime has been added with #12072 which will be part of the next Polars release.

    with pl.SQLContext(stuff=df) as ctx:
        ctx.execute(
            "select * from stuff where a = cast('2023-06-01' as date)",
            eager=True
        )
    
    shape: (2, 4)
    ┌────────────┬──────┬─────┬──────┐
    │ a          ┆ b    ┆ c   ┆ d    │
    │ ---        ┆ ---  ┆ --- ┆ ---  │
    │ date       ┆ f32  ┆ i64 ┆ f32  │
    ╞════════════╪══════╪═════╪══════╡
    │ 2023-06-01 ┆ null ┆ 4   ┆ null │
    │ 2023-06-01 ┆ null ┆ 5   ┆ null │
    └────────────┴──────┴─────┴──────┘