SELECT 
  q_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      q_products_categories.link_type = "M", 
      CONCAT(
        q_products_categories.category_id, 
        "M"
      ), 
      q_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  q_products_categories 
  INNER JOIN q_categories ON q_categories.category_id = q_products_categories.category_id 
  AND (
    q_categories.usergroup_ids = '' 
    OR FIND_IN_SET(0, q_categories.usergroup_ids) 
    OR FIND_IN_SET(1, q_categories.usergroup_ids)
  ) 
  AND q_categories.status IN ('A', 'H') 
  LEFT JOIN q_products_categories AS product_position_source ON q_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 300 
WHERE 
  q_products_categories.product_id IN (
    6415, 6416, 6417, 6418, 6419, 6420, 6421, 
    6422, 6423, 6424, 6425, 6426, 6427, 
    6428, 6429, 6430, 6431, 6432, 6433, 
    6434, 6435, 6436, 6437, 6438, 6439, 
    6440, 6441, 6442, 6443, 6444, 6445, 
    6446, 6447, 6448, 6449, 6450, 6451, 
    6452, 6453, 6454, 6456, 6457, 6458, 
    6459, 6460, 6461, 6462, 6463, 6464, 
    6465, 6466, 6467, 6468, 6469, 6470, 
    6471, 6472, 6473, 6474, 6475, 6476, 
    6477, 6478, 6479
  ) 
GROUP BY 
  q_products_categories.product_id

Query time 0.00136

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "307.21"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "q_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 64,
            "rows_produced_per_join": 64,
            "filtered": "100.00",
            "index_condition": "(`portal`.`q_products_categories`.`product_id` in (6415,6416,6417,6418,6419,6420,6421,6422,6423,6424,6425,6426,6427,6428,6429,6430,6431,6432,6433,6434,6435,6436,6437,6438,6439,6440,6441,6442,6443,6444,6445,6446,6447,6448,6449,6450,6451,6452,6453,6454,6456,6457,6458,6459,6460,6461,6462,6463,6464,6465,6466,6467,6468,6469,6470,6471,6472,6473,6474,6475,6476,6477,6478,6479))",
            "cost_info": {
              "read_cost": "140.81",
              "eval_cost": "12.80",
              "prefix_cost": "153.61",
              "data_read_per_join": "1024"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "table": {
            "table_name": "product_position_source",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id",
              "product_id"
            ],
            "key_length": "6",
            "ref": [
              "const",
              "portal.q_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 64,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "64.00",
              "eval_cost": "12.80",
              "prefix_cost": "230.41",
              "data_read_per_join": "1024"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "q_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 12,
            "filtered": "20.00",
            "cost_info": {
              "read_cost": "64.00",
              "eval_cost": "2.56",
              "prefix_cost": "307.21",
              "data_read_per_join": "33K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "(((`portal`.`q_categories`.`usergroup_ids` = '') or find_in_set(0,`portal`.`q_categories`.`usergroup_ids`) or find_in_set(1,`portal`.`q_categories`.`usergroup_ids`)) and (`portal`.`q_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}