[FEATURE]: Implement CREATE VECTOR INDEX for MySQL

[emmerich]

Feature hasn't been suggested before.

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Describe the enhancement you want to request

MySQL 9.0 is shipping with the VECTOR column type. Some MySQL providers have already start giving early access too. Additionally, Oracle has documented a VECTOR INDEX in the new version: https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/create-vector-index.html

PlanetScale also supports this syntax, but there's no way of defining it with Drizzle.

import { datetime, index, mediumtext, mysqlTable, varchar } from 'drizzle-orm/mysql-core';

const myTable = mysqlTable('my_table', {
  // a custom type implementing the VECTOR column type
  embedding: vector('embedding', { length: 1024 }),
}, (table) => ({
  embeddingIdx: vectorIndex('embedding_idx').on(table.embedding),
});

Equivalent SQL:

CREATE VECTOR INDEX embedding_idx ON my_table(embedding);

It's currently not possible even if trying to use raw SQL to define the index, so it's a bit of a blocker.