SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 266 
WHERE 
  cscart_products_categories.product_id IN (
    309474, 309478, 206988, 391625, 309476, 
    391630, 309469, 391627, 391629, 262380, 
    309470, 252156, 206990, 206986, 309475, 
    309431, 391628, 206991, 309472, 252154, 
    391631, 339432, 265269, 206468, 339433, 
    262428, 308644, 206965, 13481, 13466, 
    339434, 339438, 262429, 206983, 308657, 
    206950, 262440, 262370, 262437, 206929, 
    308646, 339439, 230172, 259698, 13488, 
    206977, 339445, 13474, 262430, 252155, 
    262436, 262434, 262432, 13486, 339440, 
    206993, 262441, 173883, 13468, 262400, 
    230173, 339511, 339515, 206933, 339441, 
    13469, 254299, 13485, 252159, 13484, 
    254297, 252157, 427782, 253161, 262359, 
    225088, 262438, 253198, 262435, 253157, 
    262439, 81573, 81586, 225081, 225074, 
    35390, 254305, 159862, 38238, 13487, 
    225053, 262399, 262394, 252161, 225066, 
    262442, 252162, 287, 81610, 286682
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00298

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "334.38"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "link_type",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 119,
            "rows_produced_per_join": 119,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "24.98",
              "eval_cost": "23.80",
              "prefix_cost": "48.78",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (309474,309478,206988,391625,309476,391630,309469,391627,391629,262380,309470,252156,206990,206986,309475,309431,391628,206991,309472,252154,391631,339432,265269,206468,339433,262428,308644,206965,13481,13466,339434,339438,262429,206983,308657,206950,262440,262370,262437,206929,308646,339439,230172,259698,13488,206977,339445,13474,262430,252155,262436,262434,262432,13486,339440,206993,262441,173883,13468,262400,230173,339511,339515,206933,339441,13469,254299,13485,252159,13484,254297,252157,427782,253161,262359,225088,262438,253198,262435,253157,262439,81573,81586,225081,225074,35390,254305,159862,38238,13487,225053,262399,262394,252161,225066,262442,252162,287,81610,286682))"
          }
        },
        {
          "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",
              "webmarco.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 119,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "119.00",
              "eval_cost": "23.80",
              "prefix_cost": "191.58",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "webmarco.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "119.00",
              "eval_cost": "1.19",
              "prefix_cost": "334.38",
              "data_read_per_join": "35K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`webmarco`.`cscart_categories`.`storefront_id` in (0,1)) and ((`webmarco`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`webmarco`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`webmarco`.`cscart_categories`.`usergroup_ids`)) and (`webmarco`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}