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 (
    42, 83, 84, 85, 86, 87, 88, 89, 147, 148, 
    149, 150, 151, 152, 153, 168, 169, 170, 
    171, 172, 173, 174, 250, 251, 252, 253, 
    254, 255, 256, 304, 305, 306, 307, 308, 
    309, 3532, 3533, 3534, 3535, 3536, 3537, 
    3538, 3947, 3948, 3949, 3950, 3951, 
    3952, 3953, 3992, 3993, 3994, 3995, 
    3996, 3997, 3998, 4052, 4053, 4054, 
    4055, 4056, 4057, 4058, 4135, 4136, 
    4137, 4138, 4139, 4140, 4141, 4188, 
    4189, 4190, 4191, 4192, 4193, 4194, 
    29, 30, 31, 32, 33, 34, 35, 76, 77, 78, 
    79, 80, 81, 82, 140, 141, 142, 143, 144
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00410

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.37"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.53"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 40,
            "rows_produced_per_join": 1,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "4.54",
              "eval_cost": "0.16",
              "prefix_cost": "4.70",
              "data_read_per_join": "6K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`gaseus`.`cscart_categories`.`storefront_id` in (0,1)) and ((`gaseus`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`gaseus`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`gaseus`.`cscart_categories`.`usergroup_ids`))) and (`gaseus`.`cscart_categories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "gaseus.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 110,
            "rows_produced_per_join": 1,
            "filtered": "0.87",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (42,83,84,85,86,87,88,89,147,148,149,150,151,152,153,168,169,170,171,172,173,174,250,251,252,253,254,255,256,304,305,306,307,308,309,3532,3533,3534,3535,3536,3537,3538,3947,3948,3949,3950,3951,3952,3953,3992,3993,3994,3995,3996,3997,3998,4052,4053,4054,4055,4056,4057,4058,4135,4136,4137,4138,4139,4140,4141,4188,4189,4190,4191,4192,4193,4194,29,30,31,32,33,34,35,76,77,78,79,80,81,82,140,141,142,143,144))",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "0.15",
              "prefix_cost": "66.30",
              "data_read_per_join": "24"
            },
            "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",
              "gaseus.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.38",
              "eval_cost": "0.15",
              "prefix_cost": "66.84",
              "data_read_per_join": "24"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}