upgrade explain example

Author: asmyasnikov

table/example_test.go

@@ -66,28 +66,37 @@ func Example_explainQuery() {
 	ctx := context.TODO()
 	db, err := ydb.Open(ctx, "grpc://localhost:2136/local")
 	if err != nil {
-		fmt.Printf("failed connect: %v", err)
-
-		return
+		panic(err)
 	}
-	defer db.Close(ctx)  // cleanup resources
+	defer db.Close(ctx) // cleanup resources
+	var (
+		plan string
+		ast  string
+	)
 	err = db.Table().Do( // Do retry operation on errors with best effort
 		ctx, // context manage exiting from Do
 		func(ctx context.Context, s table.Session) (err error) { // retry operation
-			explanation, err := s.Explain(ctx, `SELECT 42 as id, "my string" as myStr`)
+			explanation, err := s.Explain(ctx, `
+				DECLARE $id AS Optional<Uint64>;
+				DECLARE $myStr AS Optional<Text>;
+				SELECT $id AS id, $myStr AS myStr;
+			`)
 			if err != nil {
 				return err // for auto-retry with driver
 			}
 
-			fmt.Printf("plan: %s\n\nAST: %s", explanation.Plan, explanation.AST)
+			plan, ast = explanation.Plan, explanation.AST
 
 			return nil
 		},
 		table.WithIdempotent(),
 	)
 	if err != nil {
-		fmt.Printf("unexpected error: %v", err)
+		panic(err)
 	}
+
+	fmt.Printf("Plan: %s\n", plan)
+	fmt.Printf("AST: %s\n", ast)
 }
 
 func Example_createTable() {