Fix subquery alias table definition unparsing for SQLite

datafusion/sql/src/unparser/dialect.rs

@@ -102,6 +102,12 @@ pub trait Dialect: Send + Sync {
     fn date32_cast_dtype(&self) -> sqlparser::ast::DataType {
         sqlparser::ast::DataType::Date
     }
+
+    /// Does the dialect support specifying column aliases as part of alias table definition?
+    /// (SELECT col1, col2 from my_table) AS my_table_alias(col1_alias, col2_alias)
+    fn supports_column_alias_in_table_alias(&self) -> bool {
+        true
+    }
 }
 
 /// `IntervalStyle` to use for unparsing
@@ -221,6 +227,10 @@ impl Dialect for SqliteDialect {
     fn date32_cast_dtype(&self) -> sqlparser::ast::DataType {
         sqlparser::ast::DataType::Text
     }
+
+    fn supports_column_alias_in_table_alias(&self) -> bool {
+        false
+    }
 }
 
 pub struct CustomDialect {
@@ -236,6 +246,7 @@ pub struct CustomDialect {
     timestamp_cast_dtype: ast::DataType,
     timestamp_tz_cast_dtype: ast::DataType,
     date32_cast_dtype: sqlparser::ast::DataType,
+    supports_column_alias_in_table_alias: bool,
 }
 
 impl Default for CustomDialect {
@@ -256,6 +267,7 @@ impl Default for CustomDialect {
                 TimezoneInfo::WithTimeZone,
             ),
             date32_cast_dtype: sqlparser::ast::DataType::Date,
+            supports_column_alias_in_table_alias: true,
         }
     }
 }
@@ -323,6 +335,10 @@ impl Dialect for CustomDialect {
     fn date32_cast_dtype(&self) -> sqlparser::ast::DataType {
         self.date32_cast_dtype.clone()
     }
+
+    fn supports_column_alias_in_table_alias(&self) -> bool {
+        self.supports_column_alias_in_table_alias
+    }
 }
 
 /// `CustomDialectBuilder` to build `CustomDialect` using builder pattern
@@ -352,6 +368,7 @@ pub struct CustomDialectBuilder {
     timestamp_cast_dtype: ast::DataType,
     timestamp_tz_cast_dtype: ast::DataType,
     date32_cast_dtype: ast::DataType,
+    supports_column_alias_in_table_alias: bool,
 }
 
 impl Default for CustomDialectBuilder {
@@ -378,6 +395,7 @@ impl CustomDialectBuilder {
                 TimezoneInfo::WithTimeZone,
             ),
             date32_cast_dtype: sqlparser::ast::DataType::Date,
+            supports_column_alias_in_table_alias: true,
         }
     }
 
@@ -395,6 +413,8 @@ impl CustomDialectBuilder {
             timestamp_cast_dtype: self.timestamp_cast_dtype,
             timestamp_tz_cast_dtype: self.timestamp_tz_cast_dtype,
             date32_cast_dtype: self.date32_cast_dtype,
+            supports_column_alias_in_table_alias: self
+                .supports_column_alias_in_table_alias,
         }
     }
 
@@ -482,4 +502,13 @@ impl CustomDialectBuilder {
         self.date32_cast_dtype = date32_cast_dtype;
         self
     }
+
+    /// Customize the dialect to supports column aliases as part of alias table definition
+    pub fn with_supports_column_alias_in_table_alias(
+        mut self,
+        supports_column_alias_in_table_alias: bool,
+    ) -> Self {
+        self.supports_column_alias_in_table_alias = supports_column_alias_in_table_alias;
+        self
+    }
 }

datafusion/sql/src/unparser/plan.rs

@@ -15,7 +15,9 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use datafusion_common::{internal_err, not_impl_err, Column, DataFusionError, Result};
+use datafusion_common::{
+    internal_err, not_impl_err, plan_err, Column, DataFusionError, Result,
+};
 use datafusion_expr::{
     expr::Alias, Distinct, Expr, JoinConstraint, JoinType, LogicalPlan, Projection,
     SortExpr,
@@ -30,7 +32,8 @@ use super::{
         SelectBuilder, TableRelationBuilder, TableWithJoinsBuilder,
     },
     rewrite::{
-        normalize_union_schema, rewrite_plan_for_sort_on_non_projected_fields,
+        inject_column_aliases, normalize_union_schema,
+        rewrite_plan_for_sort_on_non_projected_fields,
         subquery_alias_inner_query_and_columns,
     },
     utils::{find_agg_node_within_select, unproject_window_exprs, AggVariant},
@@ -450,10 +453,33 @@ impl Unparser<'_> {
                 Ok(())
             }
             LogicalPlan::SubqueryAlias(plan_alias) => {
-                // Handle bottom-up to allocate relation
-                let (plan, columns) = subquery_alias_inner_query_and_columns(plan_alias);
+                let (plan, mut columns) =
+                    subquery_alias_inner_query_and_columns(plan_alias);
+
+                if !columns.is_empty()
+                    && !self.dialect.supports_column_alias_in_table_alias()
+                {
+                    // if columns are returned then the plan corresponds to a projection
+                    let LogicalPlan::Projection(inner_p) = plan else {
+                        return plan_err!(
+                            "Inner projection for subquery alias is expected"
+                        );
+                    };
+
+                    // Instead of specifying column aliases as part of the outer table, inject them directly into the inner projection
+                    let rewritten_plan = inject_column_aliases(inner_p, columns);
+                    columns = vec![];
+
+                    self.select_to_sql_recursively(
+                        &rewritten_plan,
+                        query,
+                        select,
+                        relation,
+                    )?;
+                } else {
+                    self.select_to_sql_recursively(plan, query, select, relation)?;
+                }
 
-                self.select_to_sql_recursively(plan, query, select, relation)?;
                 relation.alias(Some(
                     self.new_table_alias(plan_alias.alias.table().to_string(), columns),
                 ));

datafusion/sql/src/unparser/rewrite.rs

@@ -24,7 +24,7 @@ use datafusion_common::{
     tree_node::{Transformed, TransformedResult, TreeNode},
     Result,
 };
-use datafusion_expr::tree_node::transform_sort_vec;
+use datafusion_expr::{expr::Alias, tree_node::transform_sort_vec};
 use datafusion_expr::{Expr, LogicalPlan, Projection, Sort, SortExpr};
 use sqlparser::ast::Ident;
 
@@ -257,6 +257,40 @@ pub(super) fn subquery_alias_inner_query_and_columns(
     (outer_projections.input.as_ref(), columns)
 }
 
+/// Injects column aliases into the projection of a logical plan by wrapping `Expr::Column` expressions
+/// with `Expr::Alias` using the provided list of aliases. Non-column expressions are left unchanged.
+///
+/// Example:
+/// - `SELECT col1, col2 FROM table` with aliases `["alias_1", "some_alias_2"]` will be transformed to
+/// - `SELECT col1 AS alias_1, col2 AS some_alias_2 FROM table`
+pub(super) fn inject_column_aliases(
+    projection: &datafusion_expr::Projection,
+    aliases: impl IntoIterator<Item = Ident>,
+) -> LogicalPlan {
+    let mut updated_projection = projection.clone();
+
+    let new_exprs = updated_projection
+        .expr
+        .into_iter()
+        .zip(aliases)
+        .map(|(expr, col_alias)| match expr {
+            Expr::Column(col) => {
+                let relation = col.relation.clone();
+                Expr::Alias(Alias {
+                    expr: Box::new(Expr::Column(col)),
+                    relation,
+                    name: col_alias.value,
+                })
+            }
+            _ => expr,
+        })
+        .collect::<Vec<_>>();
+
+    updated_projection.expr = new_exprs;
+
+    LogicalPlan::Projection(updated_projection)
+}
+
 fn find_projection(logical_plan: &LogicalPlan) -> Option<&Projection> {
     match logical_plan {
         LogicalPlan::Projection(p) => Some(p),

datafusion/sql/tests/cases/plan_to_sql.rs

@@ -25,7 +25,7 @@ use datafusion_expr::{col, table_scan};
 use datafusion_sql::planner::{ContextProvider, PlannerContext, SqlToRel};
 use datafusion_sql::unparser::dialect::{
     DefaultDialect as UnparserDefaultDialect, Dialect as UnparserDialect,
-    MySqlDialect as UnparserMySqlDialect,
+    MySqlDialect as UnparserMySqlDialect, SqliteDialect,
 };
 use datafusion_sql::unparser::{expr_to_sql, plan_to_sql, Unparser};
 
@@ -406,7 +406,19 @@ fn roundtrip_statement_with_dialect() -> Result<()> {
             expected: r#"SELECT c.id FROM (SELECT (CAST(j1.j1_id AS BIGINT) + 1) FROM j1 ORDER BY j1.j1_id ASC NULLS LAST LIMIT 1) AS c (id)"#,
             parser_dialect: Box::new(GenericDialect {}),
             unparser_dialect: Box::new(UnparserDefaultDialect {}),
-        }
+        },
+        TestStatementWithDialect {
+            sql: "SELECT temp_j.id2 FROM (SELECT j1_id, j1_string FROM j1) AS temp_j(id2, string2)",
+            expected: r#"SELECT temp_j.id2 FROM (SELECT j1.j1_id, j1.j1_string FROM j1) AS temp_j (id2, string2)"#,
+            parser_dialect: Box::new(GenericDialect {}),
+            unparser_dialect: Box::new(UnparserDefaultDialect {}),
+        },
+        TestStatementWithDialect {
+            sql: "SELECT temp_j.id2 FROM (SELECT j1_id, j1_string FROM j1) AS temp_j(id2, string2)",
+            expected: r#"SELECT `temp_j`.`id2` FROM (SELECT `j1`.`j1_id` AS `id2`, `j1`.`j1_string` AS `string2` FROM `j1`) AS `temp_j`"#,
+            parser_dialect: Box::new(GenericDialect {}),
+            unparser_dialect: Box::new(SqliteDialect {}),
+        },
     ];
 
     for query in tests {