Remove the dependency on postgresql for table default values

[whhe]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

We are trying to use MySQL as the metabase for Dify. As discussed in https://github.com/langgenius/dify/pull/2371#issuecomment-1925683875, it is better not to use postgresql specific features. I think removing the dependency on postgresql for table default values could be a good start for this work.

2. Additional context or comments

No response

3. Can you help us with this feature?

• [x] I am interested in contributing to this feature.

[dosubot[bot]]

Hi, @whhe. I'm Dosu, and I'm helping the Dify team manage their backlog. I'm marking this issue as stale.

Issue Summary:

• Proposal to remove PostgreSQL-specific features for table default values.
• Aim is to enable compatibility with MySQL as the metabase.
• You expressed willingness to contribute to this change.
• No further comments or activities since the issue was opened.

Next Steps:

• Is this issue still relevant to the latest version of the Dify repository? If so, please comment to keep the discussion open.
• If there are no updates, the issue will be automatically closed in 15 days.

Thank you for your understanding and contribution!