A strange execution plan. One table in the association query is not associated with any other tables

1. Database version ：

8.0.13

2. Problem finding

    Monitoring found that a concurrent query caused the database to cpu High utilization rate , I found the sql See if there is room for optimization , But after looking at the implementation plan , It's strange to find this implementation plan , Let's send it to you for a look .

    We found that the execution plan shows that we visited first g surface , Then I visited a surface , The problem is g Table and a stay sql There is no associated field in , that g How does the table match a Table Association ？

Execution plan common version ：

# The table name is desensitized 
mysql> explain SELECT any_value(b.id) AS id, b.sub_order_no, any_value(b.order_no) AS order_no
    -> , any_value(b.status) AS status, any_value(b.c_m_mount) AS c_m_mount
    -> , any_value(b.c_delivery_m_fee) AS c_delivery_m_fee, any_value(b.c_i_mount) AS c_i_mount
    -> , any_value(b.c_delivery_i_fee) AS c_delivery_i_fee, any_value(c.publish_id) AS publish_id
    -> , any_value(c.publish_version_id) AS publish_version_id, any_value(c.product_version_id) AS product_version_id
    -> , any_value(c.sku_id) AS sku_id, any_value(c.num) AS num
    -> , any_value(d.delivery_no) AS delivery_no, any_value(d.delivery_status) AS delivery_status
    -> , any_value(d.delivery_code) AS delivery_code, any_value(d.delivery_com) AS delivery_com
    -> , any_value(h.pay_type) AS pay_type, any_value(h.pay_channel) AS pay_channel
    -> , any_value(g.shop_no) AS shop_no, any_value(a.create_time) AS create_time
    -> , any_value(t.id) AS user_id, any_value(e.imp_price) AS imp_price
    -> , any_value(a.address) AS address, any_value(a.tmp_order_no) AS tmp_order_no
    -> , any_value(g.shop_type) AS shop_type, any_value(t.usertype) AS source
    -> , any_value(f.pd_type) AS pd_type, any_value(e.cost_price) AS cost_price
    -> , any_value(e.market_price) AS market_price, any_value(f.source) AS product_source
    -> FROM test_od_suborder b
    -> LEFT JOIN test_od_order a ON a.order_no = b.order_no
    -> LEFT JOIN test_od_order_detail c ON b.sub_order_no = c.sub_order_no
    -> LEFT JOIN test_od_delivery d ON d.sub_order_no = b.sub_order_no
    -> LEFT JOIN test_pd_product_standard e ON e.id = c.sku_id
    -> LEFT JOIN test_pd_product f ON f.product_no = e.product_no
    -> LEFT JOIN test_pd_shop g ON f.shop_no = g.shop_no
    -> LEFT JOIN m_ac_pay h
    -> ON h.order_no = b.order_no
    -> AND h.direction = '01'
    -> LEFT JOIN b_channel_user t ON ac_userid = a.user_id
    -> WHERE a.is_delete = '0'
    -> AND g.shop_no = 'xxxxxxx'
    -> AND b.status IN ('1', '2', '3')
    -> GROUP BY b.sub_order_no
    -> ORDER BY any_value(a.create_time) DESC
    -> LIMIT 10;
+----+-------------+-------+------------+--------+----------------------------------------------------+--------------------+---------+------------------------+-------+----------+---------------------------------+
| id | select_type | table | partitions | type   | possible_keys                                      | key                | key_len | ref                    | rows  | filtered | Extra                           |
+----+-------------+-------+------------+--------+----------------------------------------------------+--------------------+---------+------------------------+-------+----------+---------------------------------+
|  1 | SIMPLE      | g     | NULL       | const  | PRIMARY                                            | PRIMARY            | 130     | const                  |     1 |   100.00 | Using temporary; Using filesort |
|  1 | SIMPLE      | a     | NULL       | ALL    | PRIMARY                                            | NULL               | NULL    | NULL                   | 82171 |    10.00 | Using where                     |
|  1 | SIMPLE      | b     | NULL       | ref    | sub_order_no,idx_status_orderno,idx_orderno_status | idx_orderno_status | 163     | fd_mall.a.order_no     |     1 |    96.17 | Using index condition           |
|  1 | SIMPLE      | c     | NULL       | ref    | sub_order_no                                       | sub_order_no       | 163     | fd_mall.b.sub_order_no |     1 |   100.00 | NULL                            |
|  1 | SIMPLE      | e     | NULL       | eq_ref | PRIMARY,product_no                                 | PRIMARY            | 130     | fd_mall.c.sku_id       |     1 |   100.00 | Using where                     |
|  1 | SIMPLE      | f     | NULL       | eq_ref | PRIMARY,shop_no                                    | PRIMARY            | 202     | fd_mall.e.product_no   |     1 |     5.00 | Using where                     |
|  1 | SIMPLE      | h     | NULL       | ref    | order_no,idx_orderno_amount_paychannel             | order_no           | 163     | fd_mall.b.order_no     |     1 |   100.00 | Using where                     |
|  1 | SIMPLE      | t     | NULL       | ref    | ac_userid                                          | ac_userid          | 163     | fd_mall.a.user_id      |     1 |   100.00 | NULL                            |
|  1 | SIMPLE      | d     | NULL       | ref    | sub_order_no                                       | sub_order_no       | 131     | fd_mall.b.sub_order_no |     1 |   100.00 | Using where                     |
+----+-------------+-------+------------+--------+----------------------------------------------------+--------------------+---------+------------------------+-------+----------+---------------------------------+
9 rows in set, 1 warning (0.01 sec)

json edition (explain format = json select ....;)

| {
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "32590.78"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "g",
              "access_type": "const",
              "possible_keys": [
                "PRIMARY"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "shop_no"
              ],
              "key_length": "130",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "0.10",
                "prefix_cost": "0.00",
                "data_read_per_join": "7K"
              },
              "used_columns": [
                "shop_no",
                "shop_type"
              ]
            }
          },
          {
            "table": {
              "table_name": "a",
              "access_type": "ALL",
              "possible_keys": [
                "PRIMARY"
              ],
              "rows_examined_per_scan": 82171,
              "rows_produced_per_join": 8217,
              "filtered": "10.00",
              "cost_info": {
                "read_cost": "8381.14",
                "eval_cost": "821.71",
                "prefix_cost": "9202.85",
                "data_read_per_join": "5M"
              },
              "used_columns": [
                "order_no",
                "tmp_order_no",
                "create_time",
                "address",
                "user_id",
                "is_delete"
              ],
              "attached_condition": "((`fd_mall`.`a`.`is_delete` = '0') and (`fd_mall`.`a`.`order_no` is not null))"
            }
          },
          {
            "table": {
              "table_name": "b",
              "access_type": "ref",
              "possible_keys": [
                "sub_order_no",
                "idx_status_orderno",
                "idx_orderno_status"
              ],
              "key": "idx_orderno_status",
              "used_key_parts": [
                "order_no"
              ],
              "key_length": "163",
              "ref": [
                "fd_mall.a.order_no"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 7903,
              "filtered": "96.18",
              "index_condition": "((`fd_mall`.`b`.`status` in ('1','2','3')) and (`fd_mall`.`a`.`order_no` = `fd_mall`.`b`.`order_no`))",
              "cost_info": {
                "read_cost": "2054.28",
                "eval_cost": "790.31",
                "prefix_cost": "12078.84",
                "data_read_per_join": "6M"
              },
              "used_columns": [
                "id",
                "sub_order_no",
                "order_no",
                "c_m_mount",
                "c_i_mount",
                "c_delivery_m_fee",
                "c_delivery_i_fee",
                "status"
              ]
            }
          },
          {
            "table": {
              "table_name": "c",
              "access_type": "ref",
              "possible_keys": [
                "sub_order_no"
              ],
              "key": "sub_order_no",
              "used_key_parts": [
                "sub_order_no"
              ],
              "key_length": "163",
              "ref": [
                "fd_mall.b.sub_order_no"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 7903,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "1975.78",
                "eval_cost": "790.31",
                "prefix_cost": "14844.93",
                "data_read_per_join": "40M"
              },
              "used_columns": [
                "id",
                "sub_order_no",
                "publish_id",
                "publish_version_id",
                "product_version_id",
                "sku_id",
                "num"
              ]
            }
          },
          {
            "table": {
              "table_name": "e",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "product_no"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "id"
              ],
              "key_length": "130",
              "ref": [
                "fd_mall.c.sku_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 7903,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "7723.11",
                "eval_cost": "790.31",
                "prefix_cost": "23358.35",
                "data_read_per_join": "45M"
              },
              "used_columns": [
                "id",
                "product_no",
                "imp_price",
                "market_price",
                "cost_price"
              ],
              "attached_condition": "(`fd_mall`.`e`.`id` = `fd_mall`.`c`.`sku_id`)"
            }
          },
          {
            "table": {
              "table_name": "f",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "shop_no"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_no"
              ],
              "key_length": "202",
              "ref": [
                "fd_mall.e.product_no"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 395,
              "filtered": "5.00",
              "cost_info": {
                "read_cost": "7182.06",
                "eval_cost": "39.52",
                "prefix_cost": "31330.73",
                "data_read_per_join": "1M"
              },
              "used_columns": [
                "product_no",
                "source",
                "shop_no",
                "pd_type"
              ],
              "attached_condition": "((`fd_mall`.`f`.`shop_no` = 'GYS100195') and (`fd_mall`.`f`.`product_no` = `fd_mall`.`e`.`product_no`))"
            }
          },
          {
            "table": {
              "table_name": "h",
              "access_type": "ref",
              "possible_keys": [
                "order_no",
                "idx_orderno_amount_paychannel"
              ],
              "key": "idx_orderno_amount_paychannel",
              "used_key_parts": [
                "order_no"
              ],
              "key_length": "163",
              "ref": [
                "fd_mall.b.order_no"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 395,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "391.75",
                "eval_cost": "39.52",
                "prefix_cost": "31761.99",
                "data_read_per_join": "564K"
              },
              "used_columns": [
                "pay_no",
                "order_no",
                "direction",
                "pay_type",
                "pay_channel"
              ],
              "attached_condition": "<if>(is_not_null_compl(h), (`fd_mall`.`h`.`direction` = '01'), true)"
            }
          },
          {
            "table": {
              "table_name": "t",
              "access_type": "ref",
              "possible_keys": [
                "ac_userid"
              ],
              "key": "ac_userid",
              "used_key_parts": [
                "ac_userid"
              ],
              "key_length": "163",
              "ref": [
                "fd_mall.a.user_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 405,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "382.46",
                "eval_cost": "40.51",
                "prefix_cost": "32184.96",
                "data_read_per_join": "2M"
              },
              "used_columns": [
                "id",
                "usertype",
                "ac_userid"
              ]
            }
          },
          {
            "table": {
              "table_name": "d",
              "access_type": "ref",
              "possible_keys": [
                "sub_order_no"
              ],
              "key": "sub_order_no",
              "used_key_parts": [
                "sub_order_no"
              ],
              "key_length": "131",
              "ref": [
                "fd_mall.b.sub_order_no"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 481,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "357.63",
                "eval_cost": "48.19",
                "prefix_cost": "32590.78",
                "data_read_per_join": "3M"
              },
              "used_columns": [
                "delivery_no",
                "sub_order_no",
                "delivery_code",
                "delivery_status",
                "delivery_com"
              ],
              "attached_condition": "<if>(is_not_null_compl(d), (`fd_mall`.`d`.`sub_order_no` = `fd_mall`.`b`.`sub_order_no`), true)"
            }
          }
        ]
      }
    }
  }
} |