From faecc311569e86145bc579b1b8df8ca87acface3 Mon Sep 17 00:00:00 2001 From: Xiaoju Wu Date: Mon, 28 Aug 2023 14:20:06 +0800 Subject: [PATCH] make binding doc clearer with examples (#14879) --- sql-plan-management.md | 64 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/sql-plan-management.md b/sql-plan-management.md index 143bdd6c78a2c..46ddffded8809 100644 --- a/sql-plan-management.md +++ b/sql-plan-management.md @@ -120,6 +120,70 @@ SELECT * FROM test . t WHERE a > ? > ``` > > 因此包含单个常量的 SQL 语句和包含被逗号连接起来多个常量的 SQL 语句，在被绑定时会被 TiDB 视作不同的 SQL 语句，需要分别创建绑定。 +> +> 例如： +> +> ```sql +> CREATE TABLE t(a INT, b INT, KEY idx(a)); +> CREATE SESSION BINDING for SELECT * FROM t WHERE a IN (?) USING SELECT /*+ use_index(t, idx) */ * FROM t WHERE a in (?); +> SHOW BINDINGS; +> +-----------------------------------------------+----------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> | Original_sql | Bind_sql | Default_db | Status | Create_time | Update_time | Charset | Collation | Source | Sql_digest | Plan_digest | +> +-----------------------------------------------+----------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> | SELECT * FROM `test` . `t` WHERE `a` IN ( ? ) | SELECT /*+ use_index(`t` `idx`)*/ * FROM `test`.`t` WHERE `a` IN (?) | test | enabled | 2023-08-23 14:15:31.472 | 2023-08-23 14:15:31.472 | utf8mb4 | utf8mb4_general_ci | manual | 8b9c4e6ab8fad5ba29b034311dcbfc8a8ce57dde2e2d5d5b65313b90ebcdebf7 | | +> +-----------------------------------------------+----------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> SELECT * FROM t WHERE a IN (1); +> SELECT @@LAST_PLAN_FROM_BINDING; +> +--------------------------+ +> | @@LAST_PLAN_FROM_BINDING | +> +--------------------------+ +> | 1 | +> +--------------------------+ +> SELECT * FROM t WHERE a IN (1,2); +> SELECT @@LAST_PLAN_FROM_BINDING; +> +--------------------------+ +> | @@LAST_PLAN_FROM_BINDING | +> +--------------------------+ +> | 0 | +> +--------------------------+ +> CREATE SESSION BINDING for SELECT * FROM t WHERE a IN (?,?) USING SELECT /*+ use_index(t, idx) */ * FROM t WHERE a IN (?,?); +> show bindings; +> +-------------------------------------------------+------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> | Original_sql | Bind_sql | Default_db | Status | Create_time | Update_time | Charset | Collation | Source | Sql_digest | Plan_digest | +> +-------------------------------------------------+------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> | SELECT * FROM `test` . `t` WHERE `a` IN ( ... ) | SELECT /*+ use_index(`t` `idx`)*/ * FROM `test`.`t` WHERE `a` IN (?,?) | test | enabled | 2023-08-23 14:16:30.762 | 2023-08-23 14:16:30.762 | utf8mb4 | utf8mb4_general_ci | manual | da38bf216db4a53e1a1e01c79ffa42306419442ad7238480bb7ac510723c8bdf | | +> | SELECT * FROM `test` . `t` WHERE `a` IN ( ? ) | SELECT /*+ use_index(`t` `idx`)*/ * FROM `test`.`t` WHERE `a` IN (?) | test | enabled | 2023-08-23 14:15:31.472 | 2023-08-23 14:15:31.472 | utf8mb4 | utf8mb4_general_ci | manual | 8b9c4e6ab8fad5ba29b034311dcbfc8a8ce57dde2e2d5d5b65313b90ebcdebf7 | | +> +-------------------------------------------------+------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> SELECT * FROM t WHERE a IN (1,2); +> SELECT @@LAST_PLAN_FROM_BINDING; +> +--------------------------+ +> | @@LAST_PLAN_FROM_BINDING | +> +--------------------------+ +> | 1 | +> +--------------------------+ +> SELECT * FROM t WHERE a IN (1,2,3); +> SELECT @@LAST_PLAN_FROM_BINDING; +> +--------------------------+ +> | @@LAST_PLAN_FROM_BINDING | +> +--------------------------+ +> | 1 | +> +--------------------------+ +> DROP SESSION BINDING for SELECT * FROM t WHERE a IN (?); +> SHOW BINDINGS; +> +-------------------------------------------------+------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> | Original_sql | Bind_sql | Default_db | Status | Create_time | Update_time | Charset | Collation | Source | Sql_digest | Plan_digest | +> +-------------------------------------------------+------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> | SELECT * FROM `test` . `t` WHERE `a` IN ( ... ) | SELECT /*+ use_index(`t` `idx`)*/ * FROM `test`.`t` WHERE `a` IN (?,?) | test | enabled | 2023-08-23 14:16:30.762 | 2023-08-23 14:16:30.762 | utf8mb4 | utf8mb4_general_ci | manual | da38bf216db4a53e1a1e01c79ffa42306419442ad7238480bb7ac510723c8bdf | | +> +-------------------------------------------------+------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+--------------------+--------+------------------------------------------------------------------+-------------+ +> SELECT * FROM t WHERE a IN (1); +> SELECT @@LAST_PLAN_FROM_BINDING; +> +--------------------------+ +> | @@LAST_PLAN_FROM_BINDING | +> +--------------------------+ +> | 0 | +> +--------------------------+ +> ``` +> 值得注意的是，如果一条 SQL 语句在 GLOBAL 和 SESSION 作用域内都有与之绑定的执行计划，因为优化器在遇到 SESSION 绑定时会忽略 GLOBAL 绑定的执行计划，该语句在 SESSION 作用域内绑定的执行计划会屏蔽掉语句在 GLOBAL 作用域内绑定的执行计划。