Support unparsing Array plan to SQL string (#13418)

* unparse construct and access

* add sql e2e roundtrip

* remove unused tests

* fix test and clippy

* fix clippy

datafusion/functions-nested/src/planner.rs

@@ -133,7 +133,6 @@ impl ExprPlanner for NestedFunctionPlanner {
 
 #[derive(Debug)]
 pub struct FieldAccessPlanner;
-
 impl ExprPlanner for FieldAccessPlanner {
     fn plan_field_access(
         &self,

datafusion/sql/src/unparser/expr.rs

@@ -18,8 +18,8 @@
 use datafusion_expr::expr::Unnest;
 use sqlparser::ast::Value::SingleQuotedString;
 use sqlparser::ast::{
-    self, BinaryOperator, Expr as AstExpr, Function, Ident, Interval, ObjectName,
-    TimezoneInfo, UnaryOperator,
+    self, Array, BinaryOperator, Expr as AstExpr, Function, Ident, Interval, ObjectName,
+    Subscript, TimezoneInfo, UnaryOperator,
 };
 use std::sync::Arc;
 use std::vec;
@@ -476,6 +476,19 @@ impl Unparser<'_> {
         &self,
         func_name: &str,
         args: &[Expr],
+    ) -> Result<ast::Expr> {
+        match func_name {
+            "make_array" => self.make_array_to_sql(args),
+            "array_element" => self.array_element_to_sql(args),
+            // TODO: support for the construct and access functions of the `map` and `struct` types
+            _ => self.scalar_function_to_sql_internal(func_name, args),
+        }
+    }
+
+    fn scalar_function_to_sql_internal(
+        &self,
+        func_name: &str,
+        args: &[Expr],
     ) -> Result<ast::Expr> {
         let args = self.function_args_to_sql(args)?;
         Ok(ast::Expr::Function(Function {
@@ -496,6 +509,29 @@ impl Unparser<'_> {
         }))
     }
 
+    fn make_array_to_sql(&self, args: &[Expr]) -> Result<ast::Expr> {
+        let args = args
+            .iter()
+            .map(|e| self.expr_to_sql(e))
+            .collect::<Result<Vec<_>>>()?;
+        Ok(ast::Expr::Array(Array {
+            elem: args,
+            named: false,
+        }))
+    }
+
+    fn array_element_to_sql(&self, args: &[Expr]) -> Result<ast::Expr> {
+        if args.len() != 2 {
+            return internal_err!("array_element must have exactly 2 arguments");
+        }
+        let array = self.expr_to_sql(&args[0])?;
+        let index = self.expr_to_sql(&args[1])?;
+        Ok(ast::Expr::Subscript {
+            expr: Box::new(array),
+            subscript: Box::new(Subscript::Index { index }),
+        })
+    }
+
     pub fn sort_to_sql(&self, sort: &Sort) -> Result<ast::OrderByExpr> {
         let Sort {
             expr,
@@ -1485,6 +1521,7 @@ mod tests {
     use datafusion_expr::{interval_month_day_nano_lit, ExprFunctionExt};
     use datafusion_functions_aggregate::count::count_udaf;
     use datafusion_functions_aggregate::expr_fn::sum;
+    use datafusion_functions_nested::expr_fn::{array_element, make_array};
     use datafusion_functions_window::row_number::row_number_udwf;
 
     use crate::unparser::dialect::{
@@ -1889,6 +1926,12 @@ mod tests {
                 }),
                 r#"UNNEST("table".array_col)"#,
             ),
+            (make_array(vec![lit(1), lit(2), lit(3)]), "[1, 2, 3]"),
+            (array_element(col("array_col"), lit(1)), "array_col[1]"),
+            (
+                array_element(make_array(vec![lit(1), lit(2), lit(3)]), lit(1)),
+                "[1, 2, 3][1]",
+            ),
         ];
 
         for (expr, expected) in tests {

datafusion/sql/tests/cases/plan_to_sql.rs

@@ -40,6 +40,8 @@ use datafusion_expr::builder::{
     table_scan_with_filter_and_fetch, table_scan_with_filters,
 };
 use datafusion_functions::core::planner::CoreFunctionPlanner;
+use datafusion_functions_nested::extract::array_element_udf;
+use datafusion_functions_nested::planner::{FieldAccessPlanner, NestedFunctionPlanner};
 use sqlparser::dialect::{Dialect, GenericDialect, MySqlDialect};
 use sqlparser::parser::Parser;
 
@@ -182,6 +184,11 @@ fn roundtrip_statement() -> Result<()> {
             SUM(id) OVER (ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS running_total
             FROM person
             GROUP BY GROUPING SETS ((id, first_name, last_name), (first_name, last_name), (last_name))"#,
+            "SELECT ARRAY[1, 2, 3]",
+            "SELECT ARRAY[1, 2, 3][1]",
+            "SELECT [1, 2, 3]",
+            "SELECT [1, 2, 3][1]",
+            "SELECT left[1] FROM array"
     ];
 
     // For each test sql string, we transform as follows:
@@ -195,10 +202,14 @@ fn roundtrip_statement() -> Result<()> {
             .try_with_sql(query)?
             .parse_statement()?;
         let state = MockSessionState::default()
+            .with_scalar_function(make_array_udf())
+            .with_scalar_function(array_element_udf())
             .with_aggregate_function(sum_udaf())
             .with_aggregate_function(count_udaf())
             .with_aggregate_function(max_udaf())
-            .with_expr_planner(Arc::new(CoreFunctionPlanner::default()));
+            .with_expr_planner(Arc::new(CoreFunctionPlanner::default()))
+            .with_expr_planner(Arc::new(NestedFunctionPlanner))
+            .with_expr_planner(Arc::new(FieldAccessPlanner));
         let context = MockContextProvider { state };
         let sql_to_rel = SqlToRel::new(&context);
         let plan = sql_to_rel.sql_statement_to_plan(statement).unwrap();
@@ -1239,6 +1250,6 @@ fn test_unnest_to_sql() {
     sql_round_trip(
         GenericDialect {},
         r#"SELECT unnest(make_array(1, 2, 2, 5, NULL)) as u1"#,
-        r#"SELECT UNNEST(make_array(1, 2, 2, 5, NULL)) AS u1"#,
+        r#"SELECT UNNEST([1, 2, 2, 5, NULL]) AS u1"#,
     );
 }