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 = 1320 
WHERE 
  cscart_products_categories.product_id IN (
    295774, 303250, 308376, 316325, 317505, 
    319376, 325547, 325710, 325715, 322000, 
    6276, 19341, 119170, 142807, 162962, 
    164053, 180420, 220516, 238478, 242500, 
    263871, 295549, 295825, 317507
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00138

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "25.50"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "link_type",
              "pt",
              "position",
              "category_position"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 24,
            "rows_produced_per_join": 24,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "2.67",
              "eval_cost": "2.40",
              "prefix_cost": "5.07",
              "data_read_per_join": "384"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`unicomps`.`cscart_products_categories`.`product_id` in (295774,303250,308376,316325,317505,319376,325547,325710,325715,322000,6276,19341,119170,142807,162962,164053,180420,220516,238478,242500,263871,295549,295825,317507))"
          }
        },
        {
          "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",
              "unicomps.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 24,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "9.62",
              "eval_cost": "2.40",
              "prefix_cost": "17.10",
              "data_read_per_join": "384"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id",
              "storefront_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "unicomps.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 4,
            "filtered": "19.97",
            "cost_info": {
              "read_cost": "6.00",
              "eval_cost": "0.48",
              "prefix_cost": "25.50",
              "data_read_per_join": "19K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`unicomps`.`cscart_categories`.`storefront_id` in (0,1)) and ((`unicomps`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`unicomps`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`unicomps`.`cscart_categories`.`usergroup_ids`))) and (`unicomps`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}