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 = 9940 
WHERE 
  cscart_products_categories.product_id IN (
    339432, 339433, 339438, 339434, 339439, 
    339445, 262432, 339440, 339441, 264700, 
    339446, 339447, 339449, 339689, 339448, 
    339450, 339435, 339442, 339443, 339436, 
    339451, 339437, 339444, 339476, 339456, 
    339550, 339461, 339454, 339547, 339471, 
    339545, 339474, 339548, 339470, 339544, 
    339455, 339543, 339549, 339698, 339472, 
    339542, 339487, 339480, 339475, 339688, 
    339546, 339687, 339690, 339462, 339700, 
    339811, 339459, 339679, 339473, 339813, 
    339678, 339465, 339457, 339477, 339541, 
    339489, 339699, 339469, 339458, 339482, 
    339685, 339468, 339453, 339730, 339731, 
    339478, 339463, 339709, 339467, 339460, 
    339808, 339464, 339806, 339810, 339701, 
    339807, 339479, 339452, 339729, 339485, 
    339809, 339812, 339484, 339483, 339466, 
    339486, 339488, 339481
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00228

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "261.54"
    },
    "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": 93,
            "rows_produced_per_join": 93,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "19.74",
              "eval_cost": "18.60",
              "prefix_cost": "38.34",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (339432,339433,339438,339434,339439,339445,262432,339440,339441,264700,339446,339447,339449,339689,339448,339450,339435,339442,339443,339436,339451,339437,339444,339476,339456,339550,339461,339454,339547,339471,339545,339474,339548,339470,339544,339455,339543,339549,339698,339472,339542,339487,339480,339475,339688,339546,339687,339690,339462,339700,339811,339459,339679,339473,339813,339678,339465,339457,339477,339541,339489,339699,339469,339458,339482,339685,339468,339453,339730,339731,339478,339463,339709,339467,339460,339808,339464,339806,339810,339701,339807,339479,339452,339729,339485,339809,339812,339484,339483,339466,339486,339488,339481))"
          }
        },
        {
          "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": 93,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "93.00",
              "eval_cost": "18.60",
              "prefix_cost": "149.94",
              "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": 4,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "93.00",
              "eval_cost": "0.93",
              "prefix_cost": "261.54",
              "data_read_per_join": "27K"
            },
            "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')))"
          }
        }
      ]
    }
  }
}