vector: various updates

[dveeden]

What is changed, added or deleted? (Required)

• "MySQL 9.0 vector data type" ... There is only one vector data type in MySQL, this is used for all 9.x versions. Removing the version number here makes this more clear.
• Update examples to match the style of other function docs
• Explain about explicit and implicit conversion between vector and text
• List what distance functions support indexing
• Add note about recommended distance function for OpenAI embeddings.

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• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)

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[gemini-code-assist]

Summary of Changes

Hello @dveeden, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

I've made several updates to the documentation related to vector data types and functions. The primary goal of these changes is to improve clarity, provide more comprehensive information, and align examples with documentation style guidelines.

Highlights

• Clarified MySQL Vector Data Type References: Updated documentation to refer to "MySQL vector data types" generally, removing the specific "9.0" version number, as the data type applies across MySQL 9.x versions.
• Enhanced Vector Function Documentation: Added a new column to the vector distance functions table to indicate which functions are supported by the VECTOR index.
• Improved Example Consistency: Standardized SQL examples for vector functions by removing the [tidb]> prompt, aligning them with common documentation practices.
• Guidance for OpenAI Embeddings: Included a note recommending VEC_COSINE_DISTANCE for use with OpenAI embeddings.
• Clarified Vector-to-Text Conversion: Expanded the explanation for VEC_FROM_TEXT to detail both implicit and explicit conversion scenarios between vector and text types.
• Precision in Terminology: Refined descriptions for vector functions, changing "same dimension" to "same number of dimensions" for greater accuracy.

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[gemini-code-assist]

Code Review

This pull request introduces several updates to the vector documentation. The changes include removing the version number from 'MySQL vector data type' for clarity, updating code examples to a consistent style, adding explanations for vector/text conversions, listing which distance functions support indexing, and adding a recommendation for OpenAI embeddings.

My review focuses on ensuring the documentation adheres to the style guide. I've suggested a minor wording change to use the second person as recommended by the style guide. Overall, the changes are clear and improve the documentation.