为含load_timestamp的表添加Valid_From&Valid_To列（支持关系回退）

Below are the standard Markdown formatting rules to structure your content:

Headings #

Use number signs (#) to define heading levels. The count of # corresponds to the heading hierarchy:

• # Level 1 Heading → # Level 1 Heading
• ## Level 2 Heading → ## Level 2 Heading
• ### Level 3 Heading → ### Level 3 Heading

List Items #

Initiate each list item with a dash (-):

• First list entry
• Second list entry
• Third list entry

Emphasized Text #

Wrap text with asterisks (*) to add emphasis:

• Italicize text: *italicized content* → italicized content
• Bold text: **bold content** → bold content

Code or Commands #

Surround code snippets or terminal commands with backticks (`):

• Inline code: npm install
• Multi-line code blocks use triple backticks:

function greet(name) {
  return `Hello, ${name}!`;
}

Quoted Text #

Prefix quoted content with greater than signs (>):

This is a quoted paragraph.
Line breaks within quotes require a leading > on each new line.

Links #

Format links by wrapping display text in square brackets ([]), followed by the target URL in parentheses (()):
[Markdown Guide](https://www.markdownguide.org) → Markdown Guide

Images #

For images, place alt text in square brackets ([]) and the image URL in parentheses (()):
[Sunset Over Mountains](https://example.com/sunset.jpg) → Sunset Over Mountains

内容的提问来源于stack exchange，提问作者0004