* Supported column name prefix __discard_column_ for discard columns in result sets

Author: asmyasnikov

CHANGELOG.md

@@ -1,3 +1,4 @@
+* Supported column name prefix `__discard_column_` for discard columns in result sets
 * Made `StatusIds_SESSION_EXPIRED` retriable for idempotent operations
 
 ## v3.55.0

internal/xsql/rows.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"database/sql/driver"
 	"io"
+	"strings"
 	"sync"
 
 	"github.com/ydb-platform/ydb-go-sdk/v3/internal/xerrors"
@@ -23,6 +24,8 @@ var (
 	_ driver.Rows                           = &single{}
 
 	_ types.Scanner = &valuer{}
+
+	ignoreColumnPrefixName = "__discard_column_"
 )
 
 type rows struct {
@@ -43,7 +46,9 @@ func (r *rows) Columns() []string {
 	})
 	cs := make([]string, 0, r.result.CurrentResultSet().ColumnCount())
 	r.result.CurrentResultSet().Columns(func(m options.Column) {
-		cs = append(cs, m.Name)
+		if !strings.HasPrefix(m.Name, ignoreColumnPrefixName) {
+			cs = append(cs, m.Name)
+		}
 	})
 	return cs
 }

tests/integration/database_sql_ignore_placeholder_test.go

@@ -0,0 +1,43 @@
+//go:build integration
+// +build integration
+
+package integration
+
+import (
+	"context"
+	"database/sql"
+	"testing"
+	"time"
+
+	"github.com/ydb-platform/ydb-go-sdk/v3"
+	"github.com/ydb-platform/ydb-go-sdk/v3/retry"
+)
+
+func TestDatabaseSqlDiscardColumn(t *testing.T) {
+	scope := newScope(t)
+	db := scope.SQLDriverWithFolder(
+		ydb.WithTablePathPrefix(scope.Folder()),
+		ydb.WithAutoDeclare(),
+		ydb.WithNumericArgs(),
+	)
+	dt := time.Date(2023, 3, 1, 16, 34, 18, 0, time.UTC)
+
+	var row *sql.Row
+	err := retry.Retry(scope.Ctx, func(ctx context.Context) (err error) {
+		row = db.QueryRowContext(ctx, `
+			SELECT 
+				$1 AS vInt,
+				$2 AS __discard_column_1,
+				$3 AS __discard_column_2,
+				$4 AS __discard_column_3 
+			`, 1, "2", 3.0, dt,
+		)
+		return row.Err()
+	})
+	scope.Require.NoError(err)
+
+	var resInt int
+	scope.Require.NoError(row.Scan(&resInt))
+
+	scope.Require.Equal(1, resInt)
+}