Improve TableScan with filters pushdown unparsing (multiple filters support) (#13131)

Author: sgrebnov

datafusion/sql/src/unparser/ast.rs

@@ -182,7 +182,28 @@ impl SelectBuilder {
         self
     }
     pub fn selection(&mut self, value: Option<ast::Expr>) -> &mut Self {
-        self.selection = value;
+        // With filter pushdown optimization, the LogicalPlan can have filters defined as part of `TableScan` and `Filter` nodes.
+        // To avoid overwriting one of the filters, we combine the existing filter with the additional filter.
+        // Example:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
+        // |  Projection: customer.c_phone AS cntrycode, customer.c_acctbal                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
+        // |   Filter: CAST(customer.c_acctbal AS Decimal128(38, 6)) > (<subquery>)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
+        // |     Subquery:
+        // |     ..                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
+        // |     TableScan: customer, full_filters=[customer.c_mktsegment = Utf8("BUILDING")]
+        match (&self.selection, value) {
+            (Some(existing_selection), Some(new_selection)) => {
+                self.selection = Some(ast::Expr::BinaryOp {
+                    left: Box::new(existing_selection.clone()),
+                    op: ast::BinaryOperator::And,
+                    right: Box::new(new_selection),
+                });
+            }
+            (None, Some(new_selection)) => {
+                self.selection = Some(new_selection);
+            }
+            (_, None) => (),
+        }
+
         self
     }
     pub fn group_by(&mut self, value: ast::GroupByExpr) -> &mut Self {

datafusion/sql/tests/cases/plan_to_sql.rs

@@ -968,6 +968,21 @@ fn test_table_scan_pushdown() -> Result<()> {
         table_scan_with_all.to_string(),
         "SELECT t1.id, t1.age FROM t1 WHERE (t1.id > t1.age) LIMIT 10"
     );
+
+    let table_scan_with_additional_filter = table_scan_with_filters(
+        Some("t1"),
+        &schema,
+        None,
+        vec![col("id").gt(col("age"))],
+    )?
+    .filter(col("id").eq(lit(5)))?
+    .build()?;
+    let table_scan_with_filter = plan_to_sql(&table_scan_with_additional_filter)?;
+    assert_eq!(
+        table_scan_with_filter.to_string(),
+        "SELECT * FROM t1 WHERE (t1.id = 5) AND (t1.id > t1.age)"
+    );
+
     Ok(())
 }