Spm fix hint issue (#18534) (#19484)

sql-plan-management.md

@@ -30,50 +30,45 @@ CREATE [GLOBAL | SESSION] BINDING [FOR BindableStmt] USING BindableStmt;
 该语句可以在 GLOBAL 或者 SESSION 作用域内为 SQL 绑定执行计划。目前，可创建执行计划绑定的 SQL 语句类型 (BindableStmt) 包括：`SELECT`、`DELETE`、`UPDATE` 和带有 `SELECT` 子查询的 `INSERT`/`REPLACE`。使用示例如下：
 
 ```sql
-CREATE GLOBAL BINDING USING SELECT /*+ use_index(t1, idx_a) */ * FROM t1;
-CREATE GLOBAL BINDING FOR SELECT * FROM t1 USING SELECT /*+ use_index(t1, idx_a) */ * FROM t1;
+CREATE GLOBAL BINDING USING SELECT /*+ use_index(orders, orders_book_id_idx) */ * FROM orders;
+CREATE GLOBAL BINDING FOR SELECT * FROM orders USING SELECT /*+ use_index(orders, orders_book_id_idx) */ * FROM orders;
 ```
 
 > **注意：**
 >
 > 绑定的优先级高于手工添加的 Hint，即在有绑定的时候执行带有 Hint 的语句时，该语句中控制优化器行为的 Hint 不会生效，但是其他类别的 Hint 仍然能够生效。
 
-其中，有两类特定的语法由于语法冲突不能创建执行计划绑定，例如：
+其中，有两类特定的语法由于语法冲突不能创建执行计划绑定，创建时会报语法错误，例如：
 
 ```sql
 -- 类型一：使用 `JOIN` 关键字但不通过 `USING` 关键字指定关联列的笛卡尔积
 CREATE GLOBAL BINDING for
-    SELECT * FROM t t1 JOIN t t2
+    SELECT * FROM orders o1 JOIN orders o2
 USING
-    SELECT * FROM t t1 JOIN t t2;
+    SELECT * FROM orders o1 JOIN orders o2;
 
 -- 类型二：包含了 `USING` 关键字的 `delete` 语句
 CREATE GLOBAL BINDING for
-    delete FROM t1 USING t1 JOIN t2 ON t1.a = t2.a
+    DELETE FROM users USING users JOIN orders ON users.id = orders.user_id
 USING
-    delete FROM t1 USING t1 JOIN t2 ON t1.a = t2.a;
+    DELETE FROM users USING users JOIN orders ON users.id = orders.user_id;
 ```
 
 可以通过等价的 SQL 改写绕过这个语法冲突的问题。例如，上述两个例子可以改写为：
 
 ```sql
--- 类型一的第一种改写：为 `JOIN` 关键字添加 `USING` 子句
-CREATE GLOBAL BINDING for
-    SELECT * FROM t t1 JOIN t t2 USING (a)
-USING
-    SELECT * FROM t t1 JOIN t t2 USING (a);
 
--- 类型一的第二种改写：去掉 `JOIN` 关键字
+-- 类型一的改写：去掉 `JOIN` 关键字，用逗号代替
 CREATE GLOBAL BINDING for
-    SELECT * FROM t t1, t t2
+    SELECT * FROM orders o1, orders o2
 USING
-    SELECT * FROM t t1, t t2;
+    SELECT * FROM orders o1, orders o2;
 
--- 类型二的改写：去掉 `delete` 语句中的 `USING` 关键字
+-- 类型二的改写：去掉 `DELETE` 语句中的 `USING` 关键字
 CREATE GLOBAL BINDING for
-    delete t1 FROM t1 JOIN t2 ON t1.a = t2.a
+    DELETE users FROM users JOIN orders ON users.id = orders.user_id
 USING
-    delete t1 FROM t1 JOIN t2 ON t1.a = t2.a;
+    DELETE users FROM users JOIN orders ON users.id = orders.user_id;
 ```
 
 > **注意：**
@@ -85,25 +80,25 @@ USING
 ```sql
 -- Hint 能生效的用法
 CREATE GLOBAL BINDING for
-    INSERT INTO t1 SELECT * FROM t2 WHERE a > 1 AND b = 1
+    INSERT INTO orders SELECT * FROM pre_orders WHERE status = 'VALID' AND created <= (NOW() - INTERVAL 1 HOUR)
 USING
-    INSERT INTO t1 SELECT /*+ use_index(@sel_1 t2, idx_a) */ * FROM t2 WHERE a > 1 AND b = 1;
+    INSERT INTO orders SELECT /*+ use_index(@sel_1 pre_orders, idx_created) */ * FROM pre_orders WHERE status = 'VALID' AND created <= (NOW() - INTERVAL 1 HOUR);
 
 -- Hint 不能生效的用法
 CREATE GLOBAL BINDING for
-    INSERT INTO t1 SELECT * FROM t2 WHERE a > 1 AND b = 1
+    INSERT INTO orders SELECT * FROM pre_orders WHERE status = 'VALID' AND created <= (NOW() - INTERVAL 1 HOUR)
 USING
-    INSERT /*+ use_index(@sel_1 t2, idx_a) */ INTO t1 SELECT * FROM t2 WHERE a > 1 AND b = 1;
+    INSERT /*+ use_index(@sel_1 pre_orders, idx_created) */ INTO orders SELECT * FROM pre_orders WHERE status = 'VALID' AND created <= (NOW() - INTERVAL 1 HOUR);
 ```
 
 如果在创建执行计划绑定时不指定作用域，隐式作用域 SESSION 会被使用。TiDB 优化器会将被绑定的 SQL 进行“标准化”处理，然后存储到系统表中。在处理 SQL 查询时，只要“标准化”后的 SQL 和系统表中某个被绑定的 SQL 语句一致，并且系统变量 [`tidb_use_plan_baselines`](/system-variables.md#tidb_use_plan_baselines-从-v40-版本开始引入) 的值为 `on`（其默认值为 `on`），即可使用相应的优化器 Hint。如果存在多个可匹配的执行计划，优化器会从中选择代价最小的一个进行绑定。
 
 `标准化`：把 SQL 中的常量变成变量参数，对空格和换行符等做标准化处理，并对查询引用到的表显式指定数据库。例如：
 
 ```sql
-SELECT * FROM t WHERE a >    1
+SELECT * FROM users WHERE balance >    100
 -- 以上语句标准化后如下：
-SELECT * FROM test . t WHERE a > ?
+SELECT * FROM bookshop . users WHERE balance > ?
 ```
 
 > **注意：**
@@ -113,11 +108,11 @@ SELECT * FROM test . t WHERE a > ?
 > 例如：
 >
 > ```sql
-> SELECT * FROM t WHERE a IN (1)
-> SELECT * FROM t WHERE a IN (1,2,3)
+> SELECT * FROM books WHERE type IN ('Novel')
+> SELECT * FROM books WHERE type IN ('Novel','Life','Education')
 > -- 以上语句标准化后如下：
-> SELECT * FROM test . t WHERE a IN ( ... )
-> SELECT * FROM test . t WHERE a IN ( ... )
+> SELECT * FROM bookshop . books WHERE type IN ( ... )
+> SELECT * FROM bookshop . books WHERE type IN ( ... )
 > ```
 >
 > 不同长度的 `IN` 表达式被标准化后，会被识别为同一条语句，因此只需要创建一条绑定，对这些表达式同时生效。