SELECT 
  t.tag_id as id, 
  tl.object_id as target_id, 
  CASE WHEN tl.object_type = 'V' THEN 'Video_Video' ELSE tl.object_type END as type, 
  t.tag 
FROM 
  cscart_tag_links tl 
  INNER JOIN cscart_tags t ON tl.tag_id = t.tag_id 
WHERE 
  tl.object_id = 317

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.30"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "tl",
          "access_type": "ref",
          "possible_keys": [
            "tag_id",
            "ids",
            "idx_tag_links_object_id"
          ],
          "key": "idx_tag_links_object_id",
          "used_key_parts": [
            "object_id"
          ],
          "key_length": "4",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 9,
          "rows_produced_per_join": 9,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "2.25",
            "eval_cost": "0.90",
            "prefix_cost": "3.15",
            "data_read_per_join": "144"
          },
          "used_columns": [
            "tag_id",
            "object_type",
            "object_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "t",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "tag_id"
          ],
          "key_length": "3",
          "ref": [
            "cscart_db.tl.tag_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 9,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "2.25",
            "eval_cost": "0.90",
            "prefix_cost": "6.30",
            "data_read_per_join": "6K"
          },
          "used_columns": [
            "tag_id",
            "tag"
          ]
        }
      }
    ]
  }
}