fix: Ensure only tables or aliases that exist are projected

datafusion/sql/src/unparser/ast.rs

@@ -155,6 +155,9 @@ impl SelectBuilder {
         self.top = value;
         self
     }
+    pub fn get_projection(&self) -> Vec<ast::SelectItem> {
+        self.projection.clone()
+    }
     pub fn projection(&mut self, value: Vec<ast::SelectItem>) -> &mut Self {
         self.projection = value;
         self
@@ -193,9 +196,9 @@ impl SelectBuilder {
             (None, Some(new_selection)) => {
                 self.selection = Some(new_selection);
             }
-            (_, None) => ()
+            (_, None) => (),
         }
-    
+
         self
     }
     pub fn group_by(&mut self, value: ast::GroupByExpr) -> &mut Self {
@@ -299,7 +302,9 @@ impl TableWithJoinsBuilder {
         self.relation = Some(value);
         self
     }
-
+    pub fn get_joins(&self) -> Vec<ast::Join> {
+        self.joins.clone()
+    }
     pub fn joins(&mut self, value: Vec<ast::Join>) -> &mut Self {
         self.joins = value;
         self
@@ -352,6 +357,25 @@ impl RelationBuilder {
     pub fn has_relation(&self) -> bool {
         self.relation.is_some()
     }
+    pub fn get_name(&self) -> Option<String> {
+        match self.relation {
+            Some(TableFactorBuilder::Table(ref value)) => {
+                value.name.as_ref().map(|a| a.to_string())
+            }
+            _ => None,
+        }
+    }
+    pub fn get_alias(&self) -> Option<String> {
+        match self.relation {
+            Some(TableFactorBuilder::Table(ref value)) => {
+                value.alias.as_ref().map(|a| a.name.to_string())
+            }
+            Some(TableFactorBuilder::Derived(ref value)) => {
+                value.alias.as_ref().map(|a| a.name.to_string())
+            }
+            _ => None,
+        }
+    }
     pub fn table(&mut self, value: TableRelationBuilder) -> &mut Self {
         self.relation = Some(TableFactorBuilder::Table(value));
         self

datafusion/sql/src/unparser/plan.rs

@@ -27,7 +27,7 @@ use datafusion_expr::{
     expr::Alias, BinaryExpr, Distinct, Expr, JoinConstraint, JoinType, LogicalPlan,
     LogicalPlanBuilder, Operator, Projection, SortExpr, TableScan,
 };
-use sqlparser::ast::{self, Ident, SetExpr};
+use sqlparser::ast::{self, display_separated, Ident, SetExpr};
 use std::{sync::Arc, vec};
 
 use super::{
@@ -162,10 +162,69 @@ impl Unparser<'_> {
             )]);
         }
 
+        // Construct a list of all the identifiers present in query sources
+        let mut all_idents = Vec::new();
+        if let Some(source_alias) = relation_builder.get_alias() {
+            all_idents.push(source_alias);
+        } else if let Some(source_name) = relation_builder.get_name() {
+            all_idents.push(source_name);
+        }
+
         let mut twj = select_builder.pop_from().unwrap();
+        twj.get_joins()
+            .iter()
+            .for_each(|join| match &join.relation {
+                ast::TableFactor::Table { alias, name, .. } => {
+                    if let Some(alias) = alias {
+                        all_idents.push(alias.name.to_string());
+                    } else {
+                        all_idents.push(name.to_string());
+                    }
+                }
+                ast::TableFactor::Derived { alias, .. } => {
+                    if let Some(alias) = alias {
+                        all_idents.push(alias.name.to_string());
+                    }
+                }
+                _ => {}
+            });
+
         twj.relation(relation_builder);
         select_builder.push_from(twj);
 
+        // Ensure that the projection contains references to sources that actually exist
+        let mut projection = select_builder.get_projection();
+        projection
+            .iter_mut()
+            .for_each(|select_item| match select_item {
+                ast::SelectItem::UnnamedExpr(ast::Expr::CompoundIdentifier(idents)) => {
+                    if idents.len() > 1 {
+                        let ident_source = display_separated(
+                            &idents
+                                .clone()
+                                .into_iter()
+                                .take(idents.len() - 1)
+                                .collect::<Vec<Ident>>(),
+                            ".",
+                        )
+                        .to_string();
+                        // If the identifier is not present in the list of all identifiers, it refers to a table that does not exist
+                        if !all_idents.contains(&ident_source) {
+                            let Some(last) = idents.last() else {
+                                unreachable!(
+                                    "CompoundIdentifier must have a last element"
+                                );
+                            };
+                            // Reset the identifiers to only the last element, which is the column name
+                            *idents = vec![last.clone()];
+                        }
+                    }
+                }
+                _ => {}
+            });
+
+        select_builder.projection(projection);
+
         Ok(SetExpr::Select(Box::new(select_builder.build()?)))
     }
 

datafusion/sql/tests/cases/plan_to_sql.rs

@@ -300,6 +300,58 @@ fn roundtrip_statement_with_dialect() -> Result<()> {
             parser_dialect: Box::new(GenericDialect {}),
             unparser_dialect: Box::new(UnparserDefaultDialect {}),
         },
+        TestStatementWithDialect {
+            sql: "select j1_id from (select ta.j1_id from j1 ta)",
+            expected:
+                // This seems like desirable behavior, but is actually hiding an underlying issue
+                // The re-written identifier is `ta`.`j1_id`, because `reconstuct_select_statement` runs before the derived projection
+                // and for some reason, the derived table alias is pre-set to `ta` for the top-level projection
+                "SELECT `j1_id` FROM (SELECT `ta`.`j1_id` FROM `j1` AS `ta`) AS `derived_projection`",
+            parser_dialect: Box::new(MySqlDialect {}),
+            unparser_dialect: Box::new(UnparserMySqlDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "select j1_id from (select ta.j1_id from j1 ta)",
+            expected:
+                "SELECT j1_id FROM (SELECT ta.j1_id FROM j1 AS ta)",
+            parser_dialect: Box::new(GenericDialect {}),
+            unparser_dialect: Box::new(UnparserDefaultDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "select j1_id from (select ta.j1_id from j1 ta) AS tbl1",
+            expected:
+                "SELECT tbl1.j1_id FROM (SELECT ta.j1_id FROM j1 AS ta) AS tbl1",
+            parser_dialect: Box::new(GenericDialect {}),
+            unparser_dialect: Box::new(UnparserDefaultDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "select j1_id, j2_id from (select ta.j1_id from j1 ta) AS tbl1, (select ta.j1_id as j2_id from j1 ta) as tbl2",
+            expected:
+                "SELECT tbl1.j1_id, tbl2.j2_id FROM (SELECT ta.j1_id FROM j1 AS ta) AS tbl1 JOIN (SELECT ta.j1_id AS j2_id FROM j1 AS ta) AS tbl2 ON true",
+            parser_dialect: Box::new(GenericDialect {}),
+            unparser_dialect: Box::new(UnparserDefaultDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "select j1_id, j2_id from (select ta.j1_id from j1 ta) AS tbl1, (select ta.j1_id as j2_id from j1 ta) as tbl2",
+            expected:
+                "SELECT `tbl1`.`j1_id`, `tbl2`.`j2_id` FROM (SELECT `ta`.`j1_id` FROM `j1` AS `ta`) AS `tbl1` JOIN (SELECT `ta`.`j1_id` AS `j2_id` FROM `j1` AS `ta`) AS `tbl2` ON true",
+            parser_dialect: Box::new(MySqlDialect {}),
+            unparser_dialect: Box::new(UnparserMySqlDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "select j1_id, j2_id from (select ta.j1_id from j1 ta), (select ta.j1_id as j2_id from j1 ta)",
+            expected:
+                "SELECT `j1_id`, `j2_id` FROM (SELECT `ta`.`j1_id` FROM `j1` AS `ta`) AS `derived_projection` JOIN (SELECT `ta`.`j1_id` AS `j2_id` FROM `j1` AS `ta`) AS `derived_projection` ON true",
+            parser_dialect: Box::new(MySqlDialect {}),
+            unparser_dialect: Box::new(UnparserMySqlDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "select j1_id, j2_id from (select ta.j1_id from j1 ta), (select ta.j1_id AS j2_id from j1 ta)",
+            expected:
+                "SELECT j1_id, j2_id FROM (SELECT ta.j1_id FROM j1 AS ta) JOIN (SELECT ta.j1_id AS j2_id FROM j1 AS ta) ON true",
+            parser_dialect: Box::new(GenericDialect {}),
+            unparser_dialect: Box::new(UnparserDefaultDialect {}),
+        },
         TestStatementWithDialect {
             sql: "SELECT j1_string from j1 join j2 on j1.j1_id = j2.j2_id order by j1_id",
             expected: r#"SELECT j1.j1_string FROM j1 JOIN j2 ON (j1.j1_id = j2.j2_id) ORDER BY j1.j1_id ASC NULLS LAST"#,