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 (
    8761, 9563, 9564, 9565, 9566, 9567, 9568, 
    9569, 9570, 9571, 9572, 9573, 9574, 
    9575, 9576, 9577, 9578, 9579, 9580, 
    9581, 9582, 9583, 9584, 9585, 9586, 
    9587, 9588, 9589, 9590, 9591, 9592, 
    9593, 9594, 9595, 9596, 9597, 9598, 
    9599, 9600, 9601, 9602, 9603, 9604, 
    9605, 9606, 9607, 9608, 9609, 9610, 
    9611, 9612, 9613, 9614, 9615, 9616, 
    9617, 9618, 9619, 9620, 9621, 9622, 
    9623, 9624, 9625, 9626, 9627, 9628, 
    9629, 9630, 9631, 9632, 9633, 9634, 
    9635, 9636, 9637, 9638, 9639, 9640, 
    9641, 10049, 10050, 10051, 10052, 10053, 
    10054, 10055, 10056, 10057, 10058, 
    10059, 10060, 10061, 10062, 10063, 
    10064
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00243

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.67"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.76"
      },
      "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": "1.00",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (8761,9563,9564,9565,9566,9567,9568,9569,9570,9571,9572,9573,9574,9575,9576,9577,9578,9579,9580,9581,9582,9583,9584,9585,9586,9587,9588,9589,9590,9591,9592,9593,9594,9595,9596,9597,9598,9599,9600,9601,9602,9603,9604,9605,9606,9607,9608,9609,9610,9611,9612,9613,9614,9615,9616,9617,9618,9619,9620,9621,9622,9623,9624,9625,9626,9627,9628,9629,9630,9631,9632,9633,9634,9635,9636,9637,9638,9639,9640,9641,10049,10050,10051,10052,10053,10054,10055,10056,10057,10058,10059,10060,10061,10062,10063,10064))",
            "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": "0.44",
              "eval_cost": "0.18",
              "prefix_cost": "66.92",
              "data_read_per_join": "28"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}