Identical query behaves differently between Expression API and SQL API regarding `streaming`

[Thomzoy]

Identical query behaves differently between Expression API and SQL API regarding `streaming`

[alexander-beedie]

On the latest compiled main these queries (via the frame API and SQL API) do seem to have identical plans, and both run successfully on the streaming engine - can see the leading 'STREAMING' in the explain output from both.

Confirmed that we see 'STREAMING' with both the join constraint a INNER JOIN b ON a.col = b.col and the slightly more ergonomic a INNER JOIN b USING(col):

a = pl.LazyFrame({"col": [1, 2, 3, 4, 5]})
b = pl.LazyFrame({"col": [1, 2, 3, 4, 5]})

joined_df = a.join(b, on="col").select("col")
print("FRAME API:\n", joined_df.explain(streaming=True))
# FRAME API: 
# STREAMING:
#    SELECT [col("col")] FROM
#     INNER JOIN:
#     LEFT PLAN ON: [col("col")]
#       DF ["col"]; PROJECT 1/1 COLUMNS; SELECTION: None
#     RIGHT PLAN ON: [col("col")]
#       DF ["col"]; PROJECT 1/1 COLUMNS; SELECTION: None
#     END INNER JOIN

joined_sql = pl.sql("SELECT col FROM a INNER JOIN b USING(col)")
print("\nSQL API:\n", joined_sql.explain(streaming=True))
# SQL API: 
# STREAMING:
#    SELECT [col("col")] FROM
#     INNER JOIN:
#     LEFT PLAN ON: [col("col")]
#       DF ["col"]; PROJECT 1/1 COLUMNS; SELECTION: None
#     RIGHT PLAN ON: [col("col")]
#       DF ["col"]; PROJECT 1/1 COLUMNS; SELECTION: None
#     END INNER JOIN

Resulting in...

shape: (5, 1)
┌─────┐
│ col │
│ --- │
│ i64 │
╞═════╡
│ 1   │
│ 2   │
│ 3   │
│ 4   │
│ 5   │
└─────┘

The SQL engine has had a lot of updates over the last few weeks, and there have been some streaming plan fixes; I think we can close this out as having been fixed on main 🤔