add meta.doc_id index for tidb (#4963)

api/core/rag/datasource/vdb/tidb_vector/tidb_vector.py

@@ -84,6 +84,8 @@ class TiDBVector(BaseVector):
                         id CHAR(36) PRIMARY KEY,
                         text TEXT NOT NULL,
                         meta JSON NOT NULL,
+                        doc_id VARCHAR(64) AS (JSON_UNQUOTE(JSON_EXTRACT(meta, '$.doc_id'))) STORED,
+                        KEY (doc_id),
                         vector VECTOR<FLOAT>({dimension}) NOT NULL COMMENT "hnsw(distance={self._distance_func})",
                         create_time DATETIME DEFAULT CURRENT_TIMESTAMP,
                         update_time DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP