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

crates/polars-sql/src/context.rs

@@ -15,7 +15,7 @@ use sqlparser::dialect::GenericDialect;
 use sqlparser::parser::{Parser, ParserOptions};
 
 use crate::function_registry::{DefaultFunctionRegistry, FunctionRegistry};
-use crate::sql_expr::{parse_sql_expr, process_join_constraint};
+use crate::sql_expr::{parse_sql_array, parse_sql_expr, process_join_constraint};
 use crate::table_functions::PolarsTableFunctions;
 
 /// The SQLContext is the main entry point for executing SQL queries.
@@ -748,6 +748,7 @@ impl SQLContext {
                 alias,
             } => {
                 polars_ensure!(!(*lateral), ComputeError: "LATERAL not supported");
+
                 if let Some(alias) = alias {
                     let lf = self.execute_query_no_ctes(subquery)?;
                     self.table_map.insert(alias.name.value.clone(), lf.clone());
@@ -756,6 +757,67 @@ impl SQLContext {
                     polars_bail!(ComputeError: "derived tables must have aliases");
                 }
             },
+            TableFactor::UNNEST {
+                alias,
+                array_exprs,
+                with_offset,
+                with_offset_alias: _,
+            } => {
+                if let Some(alias) = alias {
+                    let table_name = alias.name.value.clone();
+                    let column_names: Vec<Option<&str>> = alias
+                        .columns
+                        .iter()
+                        .map(|c| {
+                            if c.value.is_empty() {
+                                None
+                            } else {
+                                Some(c.value.as_str())
+                            }
+                        })
+                        .collect();
+
+                    let column_values: Vec<Series> = array_exprs
+                        .iter()
+                        .map(|arr| parse_sql_array(arr, self))
+                        .collect::<Result<_, _>>()?;
+
+                    polars_ensure!(!column_names.is_empty(),
+                        ComputeError:
+                        "UNNEST table alias must also declare column names, eg: {} (a,b,c)", alias.name.to_string()
+                    );
+                    if column_names.len() != column_values.len() {
+                        let plural = if column_values.len() > 1 { "s" } else { "" };
+                        polars_bail!(
+                            ComputeError:
+                            "UNNEST table alias requires {} column name{}, found {}", column_values.len(), plural, column_names.len()
+                        );
+                    }
+                    let column_series: Vec<Series> = column_values
+                        .iter()
+                        .zip(column_names.iter())
+                        .map(|(s, name)| {
+                            if let Some(name) = name {
+                                s.clone().with_name(name)
+                            } else {
+                                s.clone()
+                            }
+                        })
+                        .collect();
+
+                    let lf = DataFrame::new(column_series)?.lazy();
+                    if *with_offset {
+                        // TODO: make a PR to `sqlparser-rs` to support 'ORDINALITY'
+                        //  (note that 'OFFSET' is BigQuery-specific syntax, not PostgreSQL)
+                        polars_bail!(ComputeError: "UNNEST tables do not (yet) support WITH OFFSET/ORDINALITY");
+                    }
+                    self.table_map.insert(table_name.clone(), lf.clone());
+                    Ok((table_name.clone(), lf))
+                } else {
+                    polars_bail!(ComputeError: "UNNEST table must have an alias");
+                }
+            },
+
             // Support bare table, optional with alias for now
             _ => polars_bail!(ComputeError: "not yet implemented: {}", relation),
         }

crates/polars-sql/src/sql_expr.rs

@@ -4,6 +4,7 @@ use polars_core::export::regex;
 use polars_core::prelude::*;
 use polars_error::to_compute_err;
 use polars_lazy::prelude::*;
+use polars_ops::series::SeriesReshape;
 use polars_plan::prelude::typed_lit;
 use polars_plan::prelude::LiteralValue::Null;
 use rand::distributions::Alphanumeric;
@@ -185,6 +186,28 @@ pub(crate) struct SQLExprVisitor<'a> {
 }
 
 impl SQLExprVisitor<'_> {
+    fn array_expr_to_series(&mut self, elements: &[SQLExpr]) -> PolarsResult<Series> {
+        let array_elements = elements
+            .iter()
+            .map(|e| match e {
+                SQLExpr::Value(v) => self.visit_any_value(v, None),
+                SQLExpr::UnaryOp { op, expr } => match expr.as_ref() {
+                    SQLExpr::Value(v) => self.visit_any_value(v, Some(op)),
+                    _ => Err(polars_err!(ComputeError: "SQL expression {:?} is not yet supported", e)),
+                },
+                SQLExpr::Array(_) => {
+                    // TODO: nested arrays (handle FnMut issues)
+                    // let srs = self.array_expr_to_series(&[e.clone()])?;
+                    // Ok(AnyValue::List(srs))
+                    Err(polars_err!(ComputeError: "SQL interface does not yet support nested array literals:\n{:?}", e))
+                },
+                _ => Err(polars_err!(ComputeError: "SQL expression {:?} is not yet supported", e)),
+            })
+            .collect::<PolarsResult<Vec<_>>>()?;
+
+        Series::from_any_values("", &array_elements, true)
+    }
+
     fn visit_expr(&mut self, expr: &SQLExpr) -> PolarsResult<Expr> {
         match expr {
             SQLExpr::AllOp {
@@ -197,6 +220,7 @@ impl SQLExprVisitor<'_> {
                 compare_op,
                 right,
             } => self.visit_any(left, compare_op, right),
+            SQLExpr::Array(arr) => self.visit_array_expr(&arr.elem, true, None),
             SQLExpr::ArrayAgg(expr) => self.visit_arr_agg(expr),
             SQLExpr::Between {
                 expr,
@@ -220,7 +244,12 @@ impl SQLExprVisitor<'_> {
                 expr,
                 list,
                 negated,
-            } => self.visit_in_list(expr, list, *negated),
+            } => {
+                let expr = self.visit_expr(expr)?;
+                let elems = self.visit_array_expr(list, false, Some(&expr))?;
+                let is_in = expr.is_in(elems);
+                Ok(if *negated { is_in.not() } else { is_in })
+            },
             SQLExpr::InSubquery {
                 expr,
                 subquery,
@@ -615,6 +644,38 @@ impl SQLExprVisitor<'_> {
         }
     }
 
+    /// Visit a SQL `ARRAY` list (including `IN` values).
+    fn visit_array_expr(
+        &mut self,
+        elements: &[SQLExpr],
+        result_as_element: bool,
+        dtype_expr_match: Option<&Expr>,
+    ) -> PolarsResult<Expr> {
+        let mut elems = self.array_expr_to_series(elements)?;
+
+        // handle implicit temporal strings, eg: "dt IN ('2024-04-30','2024-05-01')".
+        // (not yet as versatile as the temporal string conversions in visit_binary_op)
+        if let (Some(Expr::Column(name)), Some(schema)) =
+            (dtype_expr_match, self.active_schema.as_ref())
+        {
+            if elems.dtype() == &DataType::String {
+                if let Some(DataType::Date | DataType::Time | DataType::Datetime(_, _)) =
+                    schema.get(name)
+                {
+                    elems = elems.strict_cast(&schema.get(name).unwrap().clone())?;
+                }
+            }
+        }
+        // if we are parsing the list as an element in a series, implode.
+        // otherwise, return the series as-is.
+        let res = if result_as_element {
+            elems.implode()?.into_series()
+        } else {
+            elems
+        };
+        Ok(lit(res))
+    }
+
     /// Visit a SQL `CAST` or `TRY_CAST` expression.
     ///
     /// e.g. `CAST(col AS INT)`, `col::int4`, or `TRY_CAST(col AS VARCHAR)`,
@@ -810,59 +871,6 @@ impl SQLExprVisitor<'_> {
         Ok(base.implode())
     }
 
-    /// Visit a SQL `IN` expression
-    fn visit_in_list(
-        &mut self,
-        expr: &SQLExpr,
-        list: &[SQLExpr],
-        negated: bool,
-    ) -> PolarsResult<Expr> {
-        let expr = self.visit_expr(expr)?;
-        let list = list
-            .iter()
-            .map(|e| {
-                if let SQLExpr::Value(v) = e {
-                    let av = self.visit_any_value(v, None)?;
-                    Ok(av)
-                } else if let SQLExpr::UnaryOp {op, expr} = e {
-                    match expr.as_ref() {
-                        SQLExpr::Value(v) => {
-                            let av = self.visit_any_value(v, Some(op))?;
-                            Ok(av)
-                        },
-                        _ => Err(polars_err!(ComputeError: "SQL expression {:?} is not yet supported", e))
-                    }
-                }else{
-                    Err(polars_err!(ComputeError: "SQL expression {:?} is not yet supported", e))
-                }
-            })
-            .collect::<PolarsResult<Vec<_>>>()?;
-
-        let mut s = Series::from_any_values("", &list, true)?;
-
-        // handle implicit temporal strings, eg: "dt IN ('2024-04-30','2024-05-01')".
-        // (not yet as versatile as the temporal string conversions in visit_binary_op)
-        if s.dtype() == &DataType::String {
-            // handle implicit temporal string comparisons, eg: "dt >= '2024-04-30'"
-            if let Expr::Column(name) = &expr {
-                if self.active_schema.is_some() {
-                    let schema = self.active_schema.as_ref().unwrap();
-                    let left_dtype = schema.get(name);
-                    if let Some(DataType::Date | DataType::Time | DataType::Datetime(_, _)) =
-                        left_dtype
-                    {
-                        s = s.strict_cast(&left_dtype.unwrap().clone())?;
-                    }
-                }
-            }
-        }
-        if negated {
-            Ok(expr.is_in(lit(s)).not())
-        } else {
-            Ok(expr.is_in(lit(s)))
-        }
-    }
-
     /// Visit a SQL subquery inside and `IN` expression.
     fn visit_in_subquery(
         &mut self,
@@ -1115,6 +1123,19 @@ pub(crate) fn parse_sql_expr(
     visitor.visit_expr(expr)
 }
 
+pub(crate) fn parse_sql_array(expr: &SQLExpr, ctx: &mut SQLContext) -> PolarsResult<Series> {
+    match expr {
+        SQLExpr::Array(arr) => {
+            let mut visitor = SQLExprVisitor {
+                ctx,
+                active_schema: None,
+            };
+            visitor.array_expr_to_series(arr.elem.as_slice())
+        },
+        _ => polars_bail!(ComputeError: "Expected array expression, found {:?}", expr),
+    }
+}
+
 fn parse_extract(expr: Expr, field: &DateTimeField) -> PolarsResult<Expr> {
     Ok(match field {
         DateTimeField::Millennium => expr.dt().millennium(),

crates/polars-sql/tests/functions_string.rs

@@ -109,3 +109,23 @@ fn test_array_to_string() {
     .unwrap();
     assert!(df_sql.equals(&df_expected));
 }
+
+#[test]
+fn test_array_literal() {
+    let mut context = SQLContext::new();
+    context.register("df", DataFrame::empty().lazy());
+
+    let sql = "SELECT [100,200,300] AS arr FROM df";
+    let df_sql = context.execute(sql).unwrap().collect().unwrap();
+    let df_expected = df! {
+        "arr" => &[100i64, 200, 300],
+    }
+    .unwrap()
+    .lazy()
+    .select(&[col("arr").implode()])
+    .collect()
+    .unwrap();
+
+    assert!(df_sql.equals(&df_expected));
+    assert!(df_sql.height() == 1);
+}

py-polars/tests/unit/sql/test_array.py

@@ -1,9 +1,39 @@
 from __future__ import annotations
 
+import pytest
+
 import polars as pl
+from polars.exceptions import ComputeError
 from polars.testing import assert_frame_equal
 
 
+def test_array_literals() -> None:
+    with pl.SQLContext(df=None, eager=True) as ctx:
+        res = ctx.execute(
+            """
+            SELECT
+              a1, a2, ARRAY_AGG(a1) AS a3, ARRAY_AGG(a2) AS a4
+            FROM (
+              SELECT
+                [10,20,30] AS a1,
+                ['a','b','c'] AS a2,
+              FROM df
+            ) tbl
+            """
+        )
+        assert_frame_equal(
+            res,
+            pl.DataFrame(
+                {
+                    "a1": [[10, 20, 30]],
+                    "a2": [["a", "b", "c"]],
+                    "a3": [[[10, 20, 30]]],
+                    "a4": [[["a", "b", "c"]]],
+                }
+            ),
+        )
+
+
 def test_array_to_string() -> None:
     data = {"values": [["aa", "bb"], [None, "cc"], ["dd", None]]}
     res = pl.DataFrame(data).sql(
@@ -25,3 +55,70 @@ def test_array_to_string() -> None:
             }
         ),
     )
+
+
+@pytest.mark.parametrize(
+    "array_keyword",
+    ["ARRAY", ""],
+)
+def test_unnest_table_function(array_keyword: str) -> None:
+    with pl.SQLContext(df=None, eager=True) as ctx:
+        res = ctx.execute(
+            f"""
+            SELECT * FROM
+              UNNEST(
+                {array_keyword}[1, 2, 3, 4],
+                {array_keyword}['ww','xx','yy','zz'],
+                {array_keyword}[23.0, 24.5, 28.0, 27.5]
+              ) AS tbl (x,y,z);
+            """
+        )
+        assert_frame_equal(
+            res,
+            pl.DataFrame(
+                {
+                    "x": [1, 2, 3, 4],
+                    "y": ["ww", "xx", "yy", "zz"],
+                    "z": [23.0, 24.5, 28.0, 27.5],
+                }
+            ),
+        )
+
+
+def test_unnest_table_function_errors() -> None:
+    with pl.SQLContext(df=None, eager=True) as ctx:
+        with pytest.raises(
+            ComputeError,
+            match=r'UNNEST table alias must also declare column names, eg: "frame data" \(a,b,c\)',
+        ):
+            ctx.execute('SELECT * FROM UNNEST([1, 2, 3]) AS "frame data"')
+
+        with pytest.raises(
+            ComputeError,
+            match="UNNEST table alias requires 1 column name, found 2",
+        ):
+            ctx.execute("SELECT * FROM UNNEST([1, 2, 3]) AS tbl (a, b)")
+
+        with pytest.raises(
+            ComputeError,
+            match="UNNEST table alias requires 2 column names, found 1",
+        ):
+            ctx.execute("SELECT * FROM UNNEST([1,2,3], [3,4,5]) AS tbl (a)")
+
+        with pytest.raises(
+            ComputeError,
+            match=r"UNNEST table must have an alias",
+        ):
+            ctx.execute("SELECT * FROM UNNEST([1, 2, 3])")
+
+        with pytest.raises(
+            ComputeError,
+            match=r"UNNEST tables do not \(yet\) support WITH OFFSET/ORDINALITY",
+        ):
+            ctx.execute("SELECT * FROM UNNEST([1, 2, 3]) tbl (colx) WITH OFFSET")
+
+        with pytest.raises(
+            ComputeError,
+            match="SQL interface does not yet support nested array literals",
+        ):
+            pl.sql_expr("[[1,2,3]] AS nested")