SELECT 
  cscart_tags.tag_id, 
  cscart_tag_links.object_id, 
  cscart_tag_links.object_type, 
  cscart_tags.tag, 
  cscart_tags.status, 
  COUNT(cscart_tag_links.tag_id) as popularity 
FROM 
  cscart_tags 
  LEFT JOIN cscart_tag_links ON cscart_tag_links.tag_id = cscart_tags.tag_id 
WHERE 
  1 
  AND cscart_tag_links.object_type = 'A' 
  AND cscart_tags.status IN ('A') 
  AND cscart_tag_links.object_id = 51 
GROUP BY 
  cscart_tags.tag_id 
ORDER BY 
  cscart_tags.tag asc

Query time 0.00345

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.70"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_tag_links",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "tag_id",
                "ids"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "object_type",
                "object_id"
              ],
              "key_length": "6",
              "ref": [
                "const",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "using_index": true,
              "cost_info": {
                "read_cost": "0.25",
                "eval_cost": "0.10",
                "prefix_cost": "0.35",
                "data_read_per_join": "16"
              },
              "used_columns": [
                "tag_id",
                "object_type",
                "object_id"
              ],
              "attached_condition": "(`s2cart`.`cscart_tag_links`.`tag_id` is not null)"
            }
          },
          {
            "table": {
              "table_name": "cscart_tags",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "tag_id"
              ],
              "key_length": "3",
              "ref": [
                "s2cart.cscart_tag_links.tag_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 0,
              "filtered": "11.11",
              "cost_info": {
                "read_cost": "0.25",
                "eval_cost": "0.01",
                "prefix_cost": "0.70",
                "data_read_per_join": "87"
              },
              "used_columns": [
                "tag_id",
                "tag",
                "status"
              ],
              "attached_condition": "(`s2cart`.`cscart_tags`.`status` = 'A')"
            }
          }
        ]
      }
    }
  }
}