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 (
    338, 331, 6705, 3932, 3134, 3116, 3126, 
    6673, 6679, 6691, 3155, 3131, 310, 303, 
    3939, 317, 3132, 3143, 3130, 3129, 3121, 
    3128, 6681, 6695, 3098, 3115, 6690, 
    6700, 12, 13, 14, 15, 16, 17, 18, 65, 66, 
    67, 68, 69, 70, 71, 119, 120, 121, 122, 
    123, 124, 125, 126, 127, 128, 129, 130, 
    131, 132, 233, 234, 235, 236, 237, 238, 
    239, 286, 287, 288, 289, 290, 291, 292, 
    3922, 3923, 3924, 3925, 3926, 3927, 
    3928, 3976, 3977, 3978, 3979, 3980, 
    3981, 3982, 4028, 4029, 4030, 4031, 
    4032, 4033, 4034, 4035, 4036, 4037, 
    4038, 4039
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00388

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "61.18"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.78"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 46,
            "rows_produced_per_join": 1,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "5.15",
              "eval_cost": "0.18",
              "prefix_cost": "5.33",
              "data_read_per_join": "7K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`test2_gaseus`.`cscart_categories`.`storefront_id` in (0,1)) and ((`test2_gaseus`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`test2_gaseus`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`test2_gaseus`.`cscart_categories`.`usergroup_ids`))) and (`test2_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": [
              "test2_gaseus.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 83,
            "rows_produced_per_join": 1,
            "filtered": "1.16",
            "index_condition": "(`test2_gaseus`.`cscart_products_categories`.`product_id` in (338,331,6705,3932,3134,3116,3126,6673,6679,6691,3155,3131,310,303,3939,317,3132,3143,3130,3129,3121,3128,6681,6695,3098,3115,6690,6700,12,13,14,15,16,17,18,65,66,67,68,69,70,71,119,120,121,122,123,124,125,126,127,128,129,130,131,132,233,234,235,236,237,238,239,286,287,288,289,290,291,292,3922,3923,3924,3925,3926,3927,3928,3976,3977,3978,3979,3980,3981,3982,4028,4029,4030,4031,4032,4033,4034,4035,4036,4037,4038,4039))",
            "cost_info": {
              "read_cost": "38.18",
              "eval_cost": "0.18",
              "prefix_cost": "58.78",
              "data_read_per_join": "28"
            },
            "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",
              "test2_gaseus.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.44",
              "eval_cost": "0.18",
              "prefix_cost": "59.40",
              "data_read_per_join": "28"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}