Re: [PR] Implement basic unnest function [arrow-datafusion]

["jayzhan211 (via GitHub)" <gi...@apache.org>]

jayzhan211 commented on code in PR #6796:
URL: https://github.com/apache/arrow-datafusion/pull/6796#discussion_r1346614106


##########
datafusion/expr/src/expr.rs:
##########
@@ -970,6 +987,43 @@ impl Expr {
     pub fn contains_outer(&self) -> bool {
         !find_out_reference_exprs(self).is_empty()
     }
+
+    /// Flatten the nested array expressions until the base array is reached.
+    /// For example:
+    ///  unnest([[1, 2, 3], [4, 5, 6]]) => unnest([1, 2, 3, 4, 5, 6])
+    pub fn flatten(&self) -> Self {
+        self.try_flatten().unwrap_or_else(|_| self.clone())
+    }
+
+    pub fn try_flatten(&self) -> Result<Self> {
+        match self {
+            Self::ScalarFunction(ScalarFunction {
+                fun: built_in_function::BuiltinScalarFunction::MakeArray,
+                args,
+            }) => {
+                let flatten_args: Vec<Expr> =
+                    args.iter().flat_map(Self::flatten_internal).collect();
+                Ok(Self::ScalarFunction(ScalarFunction {
+                    fun: built_in_function::BuiltinScalarFunction::MakeArray,
+                    args: flatten_args,
+                }))
+            }
+            _ => Err(DataFusionError::Internal(format!(

Review Comment:
   The updated version is in https://github.com/apache/arrow-datafusion/pull/7461/files



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