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 = 265 
WHERE 
  cscart_products_categories.product_id IN (
    3489, 3492, 3496, 3490, 3494, 6951, 3502, 
    3503, 3493, 3498, 3428, 3433, 3432, 
    22, 23, 24, 3933, 3934, 3935, 1334, 1335, 
    1336, 1337, 1338, 1339, 1340, 1341, 
    1342, 1343, 1344, 1355, 1356, 1357, 
    1358, 1359, 1360, 1361, 1362, 1363, 
    1364, 3688, 3689, 3690, 3691, 3692, 
    3693, 3694, 3695, 3696, 3697, 3709, 
    3710, 3711, 3712, 3713, 3714, 3715, 
    3716, 3717, 3718, 3708, 3152, 25, 1365, 
    3138, 3149, 6719, 3146, 3150, 1345, 
    1346, 1347, 1348, 1349, 1350, 1351, 
    1352, 1353, 1354, 3698, 3699, 3700, 
    3701, 3702, 3703, 3704, 3705, 3706, 
    3707, 6723, 6717, 6720, 3151, 3864, 
    3145, 6721
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00271

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.74"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.80"
      },
      "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": "1.03",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (3489,3492,3496,3490,3494,6951,3502,3503,3493,3498,3428,3433,3432,22,23,24,3933,3934,3935,1334,1335,1336,1337,1338,1339,1340,1341,1342,1343,1344,1355,1356,1357,1358,1359,1360,1361,1362,1363,1364,3688,3689,3690,3691,3692,3693,3694,3695,3696,3697,3709,3710,3711,3712,3713,3714,3715,3716,3717,3718,3708,3152,25,1365,3138,3149,6719,3146,3150,1345,1346,1347,1348,1349,1350,1351,1352,1353,1354,3698,3699,3700,3701,3702,3703,3704,3705,3706,3707,6723,6717,6720,3151,3864,3145,6721))",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "0.18",
              "prefix_cost": "66.30",
              "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",
              "gaseus.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.45",
              "eval_cost": "0.18",
              "prefix_cost": "66.93",
              "data_read_per_join": "28"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}