fix: sqlite recursive union

internal/dbtest/db_test.go

@@ -291,6 +291,7 @@ func TestDB(t *testing.T) {
 		{testScanRawMessage},
 		{testPointers},
 		{testExists},
+		{testRecursiveCTEUnion},
 		{testScanTimeIntoString},
 		{testModelNonPointer},
 		{testBinaryData},
@@ -1347,6 +1348,55 @@ func testExists(t *testing.T, db *bun.DB) {
 	require.False(t, exists)
 }
 
+func testRecursiveCTEUnion(t *testing.T, db *bun.DB) {
+	if !db.Dialect().Features().Has(feature.CTE) {
+		t.Skip("CTE is not supported")
+		return
+	}
+
+	if db.Dialect().Name() == dialect.MSSQL {
+		t.Skip("MSSQL uses a different recursive CTE syntax")
+		return
+	}
+
+	type Model struct {
+		bun.BaseModel `bun:"test_models,alias:m"`
+		ID            int64  `bun:",pk,autoincrement"`
+		Name          string `bun:",notnull"`
+		ParentID      *int64
+	}
+
+	mustResetModel(t, ctx, db, (*Model)(nil))
+
+	root := &Model{Name: "root"}
+	_, err := db.NewInsert().Model(root).Exec(ctx)
+	require.NoError(t, err)
+	child := &Model{Name: "child", ParentID: &root.ID}
+	_, err = db.NewInsert().Model(child).Exec(ctx)
+	require.NoError(t, err)
+	grand := &Model{Name: "grand", ParentID: &child.ID}
+	_, err = db.NewInsert().Model(grand).Exec(ctx)
+	require.NoError(t, err)
+
+	query := db.NewSelect().
+		WithRecursive("category_tree", db.NewSelect().
+			Model((*Model)(nil)).
+			Where("name LIKE ?", "%roo%").
+			UnionAll(
+				db.NewSelect().
+					Model((*Model)(nil)).
+					Join("JOIN ? AS ?", bun.Ident("category_tree"), bun.Ident("ct")).
+					JoinOn("?TableAlias.? = ?", bun.Ident("parent_id"), bun.Ident("ct.id")),
+			),
+		).
+		TableExpr("?", bun.Ident("category_tree")).
+		OrderExpr("id")
+
+	var cats []Model
+	require.NoError(t, query.Scan(ctx, &cats))
+	require.Equal(t, []string{"root", "child", "grand"}, []string{cats[0].Name, cats[1].Name, cats[2].Name})
+}
+
 func testScanTimeIntoString(t *testing.T, db *bun.DB) {
 	ctx := context.Background()
 

query_base.go

@@ -339,7 +339,14 @@ func (q *baseQuery) appendCTE(
 		b = append(b, " AS ("...)
 	}
 
-	b, err = cte.query.AppendQuery(gen, b)
+	if sq, ok := cte.query.(*SelectQuery); ok && gen.Dialect().Name() == dialect.SQLite {
+		saved := sq.skipUnionParens
+		sq.skipUnionParens = true
+		b, err = cte.query.AppendQuery(gen, b)
+		sq.skipUnionParens = saved
+	} else {
+		b, err = cte.query.AppendQuery(gen, b)
+	}
 	if err != nil {
 		return nil, err
 	}

query_select.go

@@ -31,8 +31,9 @@ type SelectQuery struct {
 	having     []schema.QueryWithArgs
 	selFor     schema.QueryWithArgs
 
-	union   []union
-	comment string
+	union           []union
+	skipUnionParens bool
+	comment         string
 }
 
 var _ Query = (*SelectQuery)(nil)
@@ -537,7 +538,10 @@ func (q *SelectQuery) appendQuery(
 		b = append(b, "WITH _count_wrapper AS ("...)
 	}
 
-	if len(q.union) > 0 {
+	hasUnion := len(q.union) > 0
+	wrapUnion := !q.skipUnionParens
+
+	if hasUnion && wrapUnion {
 		b = append(b, '(')
 	}
 
@@ -665,17 +669,23 @@ func (q *SelectQuery) appendQuery(
 		}
 	}
 
-	if len(q.union) > 0 {
-		b = append(b, ')')
+	if hasUnion {
+		if wrapUnion {
+			b = append(b, ')')
+		}
 
 		for _, u := range q.union {
 			b = append(b, u.expr...)
-			b = append(b, '(')
+			if wrapUnion {
+				b = append(b, '(')
+			}
 			b, err = u.query.AppendQuery(gen, b)
 			if err != nil {
 				return nil, err
 			}
-			b = append(b, ')')
+			if wrapUnion {
+				b = append(b, ')')
+			}
 		}
 	}