database/gdb: performance improvement in fields grouping when inserting batch data

[gqcn]

Description

There might be some performance improvement should be done here in the loop:

Additional

No response

[github-actions]

Hello @gqcn. We like your proposal/feedback and would appreciate a contribution via a Pull Request by you or another community member. We thank you in advance for your contribution and are looking forward to reviewing it!
你好 @gqcn。我们喜欢您的提案/反馈，并希望您或其他社区成员通过拉取请求做出贡献。我们提前感谢您的贡献，并期待对其进行审查。