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 = 2 
WHERE 
  cscart_products_categories.product_id IN (
    51480, 51479, 51494, 51495, 132, 112, 
    3, 78, 2, 77, 87, 66, 22421, 22424, 22290, 
    50981, 50982, 133, 45, 143, 50983, 51416, 
    51043, 51421, 51471, 51413, 51057, 
    51472, 51547, 51470, 51500, 51412, 
    51529, 51459, 51457, 51460, 51501, 
    51530, 51464, 51051, 51053, 51551, 
    51478, 51469, 51510, 51486, 51531, 
    51467, 51047, 51461, 51044, 51475, 
    51477, 51473, 51437, 51540, 51048, 
    51525, 51458, 51463, 51516, 51532, 
    51545, 51492
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00332

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "121.81"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 92,
            "rows_produced_per_join": 92,
            "filtered": "100.00",
            "index_condition": "(`test_uchur_k`.`cscart_products_categories`.`product_id` in (51480,51479,51494,51495,132,112,3,78,2,77,87,66,22421,22424,22290,50981,50982,133,45,143,50983,51416,51043,51421,51471,51413,51057,51472,51547,51470,51500,51412,51529,51459,51457,51460,51501,51530,51464,51051,51053,51551,51478,51469,51510,51486,51531,51467,51047,51461,51044,51475,51477,51473,51437,51540,51048,51525,51458,51463,51516,51532,51545,51492))",
            "cost_info": {
              "read_cost": "48.21",
              "eval_cost": "9.20",
              "prefix_cost": "57.41",
              "data_read_per_join": "1K"
            },
            "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",
              "test_uchur_k.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 92,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "23.00",
              "eval_cost": "9.20",
              "prefix_cost": "89.61",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "test_uchur_k.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 4,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "23.00",
              "eval_cost": "0.46",
              "prefix_cost": "121.81",
              "data_read_per_join": "24K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`test_uchur_k`.`cscart_categories`.`storefront_id` in (0,1)) and ((`test_uchur_k`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`test_uchur_k`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`test_uchur_k`.`cscart_categories`.`usergroup_ids`))) and (`test_uchur_k`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}