cte

data/3.MySQL高阶/3.SQL高级技巧/1.CTE和递归查询/config.json

@@ -7,7 +7,8 @@
   ],
   "children": [],
   "export": [
-    "continuous.json"
+    "continuous.json",
+    "to_root.json"
   ],
   "keywords_must": [
     "cte",

data/3.MySQL高阶/3.SQL高级技巧/1.CTE和递归查询/to_root.json

+{
+  "type": "code_options",
+  "author": "ccat",
+  "source": "to_root.md",
+  "notebook_enable": false,
+  "exercise_id": "f249526bc9294eb886de5570896cdbf3"
+}
\ No newline at end of file

data/3.MySQL高阶/3.SQL高级技巧/1.CTE和递归查询/to_root.md

+# 树结构溯根
+
+现有一个表 node
+
+```mysql
+create table node
+(
+    id      int primary key auto_increment,
+    pid     integer,
+    val integer
+);
+```
+
+其 pid 列引用 id 列，形成一个树结构，根节点的 pid 为 0。
+
+现在我们希望写一个查询，找到某一个给定id的记录，其父节点、父节点的父节点，直至根节点的路径。那么这个查询应该是：
+
+## 答案
+
+```mysql
+with recursive t(id, pid, val) as (
+    select id, pid, val
+    from node
+    where id = $1
+    union all
+    select node.id, node.pid, node.val
+    from node
+             join t on node.id = t.pid)
+select node.id, node.pid, node.val
+from node
+         join t on node.id = t.id;
+```
+
+## 选项
+
+### 没有递归定义
+
+```mysql
+with t as (
+    select id, pid, val
+    from node
+    where id = $1
+    union all
+    select node.id, node.pid, node.level
+    from node
+             join t on node.id = t.pid)
+select node.id, node.pid, node.val
+from node
+         join t on node.id = t.id;
+```
+
+### 平凡的连接查询无法处理递归问题
+
+```mysql
+select node.id, node.pid, node.val
+from node
+         join node as p on node.pid = p.id
+where id = $1;
+```
+
+### 子查询无法处理递归问题
+
+```mysql
+select node.id, node.pid, node val
+from node as t
+where t.pid = (select id from t where id = t.pid)
+```
\ No newline at end of file

data/3.MySQL高阶/3.SQL高级技巧/7.索引和优化/daily_payment.md

@@ -20,7 +20,7 @@ mysql> desc payment;
 | customer_id   | int           | YES  |     | NULL    |                |
 | staff_id      | int           | YES  |     | NULL    |                |
 | rental_id     | int           | YES  |     | NULL    |                |
-| amount        | decimal(12,8) | YES  |     | NULL    |                |
+| amount        | decimal(12,4) | YES  |     | NULL    |                |
 | pathment_date | timestamp     | YES  |     | NULL    |                |
 +---------------+---------------+------+-----+---------+----------------+
 6 rows in set (0.12 sec)

data/3.MySQL高阶/5.设计优化/6.增加中间表/config.json

 {
   "node_id": "mysql-a2ddae1b044149ecbb74db3b6eb32721",
-  "keywords": ["middle", "中间表"],
+  "keywords": [
+    "middle",
+    "中间表"
+  ],
   "children": [],
-  "export": [],
+  "export": [
+    "daily_payment2.json"
+  ],
   "keywords_must": [],
   "keywords_forbid": [],
   "group": 0

data/3.MySQL高阶/5.设计优化/6.增加中间表/daily_payment2.json

+{
+  "type": "code_options",
+  "author": "ccat",
+  "source": "daily_payment2.md",
+  "notebook_enable": false,
+  "exercise_id": "71343fd41e5d4af5a5876849e77a3be2"
+}
\ No newline at end of file

data/3.MySQL高阶/5.设计优化/6.增加中间表/daily_payment2.md

+# 每日报表优化
+
+# 每日报表
+
+分析过去一段时间的查询数据，Joe 发现 payment 表
+```mysql
+create table payment(
+    payment_id int primary key auto_increment,
+    customer_id int,
+    staff_id int,
+    rental_id int,
+    amount decimal(12, 4),
+    payment_date timestamp
+)
+```
+每天的订单量很大，下面这个查询的统计过程占用了大多数数据库资源，查询不会
+早于当天，总是在历史上某一个日期段内查询
+
+```mysql
+select date(payment_date) as day, sum(amount)
+from payment
+where date(payment_date) between $1 and $2
+group by date(payment_date);
+```
+
+
+怎样优化最有效？
+
+##  答案
+
+建立中间表并建立索引。
+
+```postgresql
+create table daily_payment(day date primary key , amount decimal(12, 4));
+
+insert into daily_payment(day, amount) 
+select payment_date::date as day, sum(amount) as amount from payment group by day;
+
+```
+
+使用
+
+```mysql
+select day, amount from view_daily_payment where day between $1 and $2;
+```
+
+进行查询。并且每天定时执行一次刷新命令
+
+```mysql
+insert into daily_payment(day, amount)
+select date(payment_date) as day, sum(amount) as amount 
+from payment
+where date(payment_date) between DATE_SUB(CURDATE(), INTERVAL 2 DAY) and DATE_SUB(CURDATE(), INTERVAL 1 DAY) 
+group by day;
+
+```
+
+## 选项
+
+### 不会优化 sum 和 group by
+
+在 payment_date 列上建立索引
+
+```mysql
+create index idx_payment_date on payment(payment_date);
+```
+
+### 不会优化 sum
+
+建立计算列
+
+```mysql
+alter table payment add day date generated always as ( payment_date::date ) stored 
+```
+
+然后使用它改写查询
+
+```mysql
+select day as day, sum(amount)
+from payment
+where day between $1 and DATE_SUB(CURDATE(), INTERVAL 1 DAY)
+group by day;
+```
+
+### 优化了日期查询，但是不会优化统计过程
+
+建立表达式索引
+
+```mysql
+create index idx_payment_day on payment((date(payment_date)));
+```
+
+### 不做物化，对查询速度不会有显著改善
+
+建立视图
+
+```mysql
+create view view_daily_payment as select date(payment_date) as day, amount from payment;
+```
+
+然后在视图 view_daily_payment 上执行
+
+```mysql
+select day, sum(amount) 
+from view_daily_payment
+where day between $1 and date('yesterday')
+group by day 
+```
\ No newline at end of file