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 (
    1906, 1907, 1908, 1909, 1910, 1911, 1912, 
    1913, 1914, 1915, 1916, 1917, 1918, 
    1919, 1920, 1921, 1922, 1923, 1924, 
    1925, 1926, 1927, 1928, 1929, 1930, 
    1931, 5560, 5561, 5562, 5563, 5564, 
    5565, 5566, 5567, 5568, 5569, 5570, 
    5571, 5572, 5573, 5574, 5575, 5576, 
    5577, 5578, 5579, 5580, 5581, 5582, 
    5583, 5584, 5585, 5586, 5587, 5588, 
    5589, 5590, 5591, 5592, 5593, 5594, 
    5595, 5596, 5597, 5598, 5599, 5600, 
    5601, 5602, 5603, 5604, 5605, 5606, 
    5607, 5608, 5609, 5610, 5611, 5612, 
    1423, 1424, 1425, 1426, 1427, 5136, 
    5137, 5138, 5139, 5140, 5141, 6711, 
    1455, 5164, 1445, 5154, 1456
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00294

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "61.38"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.92"
      },
      "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": "1.26",
            "index_condition": "(`test2_gaseus`.`cscart_products_categories`.`product_id` in (1906,1907,1908,1909,1910,1911,1912,1913,1914,1915,1916,1917,1918,1919,1920,1921,1922,1923,1924,1925,1926,1927,1928,1929,1930,1931,5560,5561,5562,5563,5564,5565,5566,5567,5568,5569,5570,5571,5572,5573,5574,5575,5576,5577,5578,5579,5580,5581,5582,5583,5584,5585,5586,5587,5588,5589,5590,5591,5592,5593,5594,5595,5596,5597,5598,5599,5600,5601,5602,5603,5604,5605,5606,5607,5608,5609,5610,5611,5612,1423,1424,1425,1426,1427,5136,5137,5138,5139,5140,5141,6711,1455,5164,1445,5154,1456))",
            "cost_info": {
              "read_cost": "38.18",
              "eval_cost": "0.19",
              "prefix_cost": "58.78",
              "data_read_per_join": "30"
            },
            "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": "0.48",
              "eval_cost": "0.19",
              "prefix_cost": "59.46",
              "data_read_per_join": "30"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}