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 = 294 
WHERE 
  cscart_products_categories.product_id IN (
    1909, 1145, 1127, 1126, 1125, 1124, 1123, 
    1111, 1110, 1109, 1108, 1107, 1053, 
    1051, 1050, 1049, 1048, 960, 959, 958, 
    957, 941, 940, 939, 929, 928, 927, 919, 
    918, 917, 517, 516, 515, 424, 423, 422, 
    421, 420, 419, 373, 351, 350
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00315

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "46.51"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "13.63"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 59,
            "rows_produced_per_join": 2,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "6.40",
              "eval_cost": "0.24",
              "prefix_cost": "6.64",
              "data_read_per_join": "6K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`wearethehelpful_scalesta_net`.`cscart_categories`.`storefront_id` in (0,1)) and ((`wearethehelpful_scalesta_net`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`wearethehelpful_scalesta_net`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`wearethehelpful_scalesta_net`.`cscart_categories`.`usergroup_ids`))) and (`wearethehelpful_scalesta_net`.`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": [
              "wearethehelpful_scalesta_net.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 26,
            "rows_produced_per_join": 13,
            "filtered": "22.21",
            "index_condition": "(`wearethehelpful_scalesta_net`.`cscart_products_categories`.`product_id` in (1909,1145,1127,1126,1125,1124,1123,1111,1110,1109,1108,1107,1053,1051,1050,1049,1048,960,959,958,957,941,940,939,929,928,927,919,918,917,517,516,515,424,423,422,421,420,419,373,351,350))",
            "cost_info": {
              "read_cost": "15.34",
              "eval_cost": "1.36",
              "prefix_cost": "28.11",
              "data_read_per_join": "218"
            },
            "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",
              "wearethehelpful_scalesta_net.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 13,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "3.41",
              "eval_cost": "1.36",
              "prefix_cost": "32.88",
              "data_read_per_join": "218"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}