CREATE [GLOBAL|SESSION] BINDING
该语句用于在 TiDB 中创建新的执行计划绑定。绑定可以用于向语句中注入 Hint，而无需更改底层查询。
BINDING 可以是 GLOBAL（全局）或 SESSION（会话）级别。默认级别为 SESSION。
被绑定的 SQL 语句会被参数化并存储在系统表中。当 SQL 查询被处理时，只要参数化后的 SQL 语句与系统表中的绑定语句一致，并且系统变量 tidb_use_plan_baselines 设置为 ON（默认），则会应用相应的优化器 Hint。如果存在多个执行计划，优化器会选择成本最低的绑定计划。更多信息请参见 创建绑定。
语法
- CreateBindingStmt
- GlobalScope
- BindableStmt
- StringLiteralOrUserVariableList
- StringLiteralOrUserVariable
示例
你可以根据 SQL 语句或历史执行计划创建绑定。
当你根据历史执行计划创建绑定时，需要指定对应的 Plan Digest：
- 你可以使用字符串字面量或字符串类型的用户变量来指定 Plan Digest。
- 你可以指定多个 Plan Digest，以便同时为多条语句创建绑定。在这种情况下，你可以指定多个字符串，并在每个字符串中包含多个 digest。注意字符串或 digest 之间需要用逗号分隔。
以下示例展示了如何根据 SQL 语句创建绑定。
mysql> CREATE TABLE t1 (
id INT NOT NULL PRIMARY KEY auto_increment,
b INT NOT NULL,
pad VARBINARY(255),
INDEX(b)
);
Query OK, 0 rows affected (0.07 sec)
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM dual;
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 8 rows affected (0.00 sec)
Records: 8 Duplicates: 0 Warnings: 0
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 1000 rows affected (0.04 sec)
Records: 1000 Duplicates: 0 Warnings: 0
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 100000 rows affected (1.74 sec)
Records: 100000 Duplicates: 0 Warnings: 0
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 100000 rows affected (2.15 sec)
Records: 100000 Duplicates: 0 Warnings: 0
mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 100000 rows affected (2.64 sec)
Records: 100000 Duplicates: 0 Warnings: 0
mysql> SELECT SLEEP(1);
+----------+
| SLEEP(1) |
+----------+
| 0 |
+----------+
1 row in set (1.00 sec)
mysql> ANALYZE TABLE t1;
Query OK, 0 rows affected (1.33 sec)
mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
+-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
+-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
| IndexLookUp_10 | 583.00 | 297 | root | | time:10.545072ms, loops:2, rpc num: 1, rpc time:398.359µs, proc keys:297 | | 109.1484375 KB | N/A |
| ├─IndexRangeScan_8(Build) | 583.00 | 297 | cop[tikv] | table:t1, index:b(b) | time:0s, loops:4 | range:[123,123], keep order:false | N/A | N/A |
| └─TableRowIDScan_9(Probe) | 583.00 | 297 | cop[tikv] | table:t1 | time:12ms, loops:4 | keep order:false | N/A | N/A |
+-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
3 rows in set (0.02 sec)
mysql> CREATE SESSION BINDING FOR
SELECT * FROM t1 WHERE b = 123
USING
SELECT * FROM t1 IGNORE INDEX (b) WHERE b = 123;
Query OK, 0 rows affected (0.00 sec)
mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
+-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
+-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
| TableReader_7 | 583.00 | 297 | root | | time:222.32506ms, loops:2, rpc num: 1, rpc time:222.078952ms, proc keys:301010 | data:Selection_6 | 88.6640625 KB | N/A |
| └─Selection_6 | 583.00 | 297 | cop[tikv] | | time:224ms, loops:298 | eq(test.t1.b, 123) | N/A | N/A |
| └─TableFullScan_5 | 301010.00 | 301010 | cop[tikv] | table:t1 | time:220ms, loops:298 | keep order:false | N/A | N/A |
+-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
3 rows in set (0.22 sec)
mysql> SHOW SESSION BINDINGS\G
*************************** 1. row ***************************
Original_sql: select * from t1 where b = ?
Bind_sql: SELECT * FROM t1 IGNORE INDEX (b) WHERE b = 123
Default_db: test
Status: using
Create_time: 2020-05-22 14:38:03.456
Update_time: 2020-05-22 14:38:03.456
Charset: utf8mb4
Collation: utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
mysql> DROP SESSION BINDING FOR SELECT * FROM t1 WHERE b = 123;
Query OK, 0 rows affected (0.00 sec)
mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
+-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
+-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
| IndexLookUp_10 | 583.00 | 297 | root | | time:5.31206ms, loops:2, rpc num: 1, rpc time:665.927µs, proc keys:297 | | 109.1484375 KB | N/A |
| ├─IndexRangeScan_8(Build) | 583.00 | 297 | cop[tikv] | table:t1, index:b(b) | time:0s, loops:4 | range:[123,123], keep order:false | N/A | N/A |
| └─TableRowIDScan_9(Probe) | 583.00 | 297 | cop[tikv] | table:t1 | time:0s, loops:4 | keep order:false | N/A | N/A |
+-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
3 rows in set (0.01 sec)以下示例展示了如何根据历史执行计划创建绑定。
USE test;
CREATE TABLE t1(a INT, b INT, c INT, INDEX ia(a));
CREATE TABLE t2(a INT, b INT, c INT, INDEX ia(a));
INSERT INTO t1 SELECT * FROM t2 WHERE a = 1;
SELECT @@LAST_PLAN_FROM_BINDING;
UPDATE /*+ INL_JOIN(t2) */ t1, t2 SET t1.a = 1 WHERE t1.b = t2.a;
SELECT @@LAST_PLAN_FROM_BINDING;
DELETE /*+ HASH_JOIN(t1) */ t1 FROM t1 JOIN t2 WHERE t1.b = t2.a;
SELECT @@LAST_PLAN_FROM_BINDING;
SELECT * FROM t1 WHERE t1.a IN (SELECT a FROM t2);
SELECT @@LAST_PLAN_FROM_BINDING;方法一：
SELECT query_sample_text, stmt_type, table_names, plan_digest FROM information_schema.statements_summary_history WHERE table_names LIKE '%test.t1%' AND stmt_type != 'CreateTable';
CREATE GLOBAL BINDING FROM HISTORY USING PLAN DIGEST 'e72819cf99932f63a548156dbf433adda60e10337e89dcaa8638b4caf16f64d8,c291edc36b2482738d3389d335f37efc76290be2930330fe5034c5f4c42eeb36,8dc146249484f4a6ab219bfe9effa6b7a18aeed3764d49b610da61ac347ab914,73b2dec866595688ea416675f88ccb3456eb8e7443a79cd816695b688e07ac6b';方法二：
SELECT @digests:=GROUP_CONCAT(plan_digest) FROM information_schema.statements_summary_history WHERE table_names LIKE '%test.t1%' AND stmt_type != 'CreateTable';
CREATE GLOBAL BINDING FROM HISTORY USING PLAN DIGEST @digests;SHOW GLOBAL BINDINGS;
INSERT INTO t1 SELECT * FROM t2 WHERE a = 1;
SELECT @@LAST_PLAN_FROM_BINDING;
UPDATE t1, t2 SET t1.a = 1 WHERE t1.b = t2.a;
SELECT @@LAST_PLAN_FROM_BINDING;
DELETE t1 FROM t1 JOIN t2 WHERE t1.b = t2.a;
SELECT @@LAST_PLAN_FROM_BINDING;
SELECT * FROM t1 WHERE t1.a IN (SELECT a FROM t2);
SELECT @@LAST_PLAN_FROM_BINDING;> CREATE TABLE t1(a INT, b INT, c INT, INDEX ia(a));
Query OK, 0 rows affected (0.048 sec)
> CREATE TABLE t2(a INT, b INT, c INT, INDEX ia(a));
Query OK, 0 rows affected (0.035 sec)
> INSERT INTO t1 SELECT * FROM t2 WHERE a = 1;
Query OK, 0 rows affected (0.002 sec)
Records: 0 Duplicates: 0 Warnings: 0
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 0 |
+--------------------------+
1 row in set (0.001 sec)
> UPDATE /*+ INL_JOIN(t2) */ t1, t2 SET t1.a = 1 WHERE t1.b = t2.a;
Query OK, 0 rows affected (0.005 sec)
Rows matched: 0 Changed: 0 Warnings: 0
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 0 |
+--------------------------+
1 row in set (0.000 sec)
> DELETE /*+ HASH_JOIN(t1) */ t1 FROM t1 JOIN t2 WHERE t1.b = t2.a;
Query OK, 0 rows affected (0.003 sec)
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 0 |
+--------------------------+
1 row in set (0.000 sec)
> SELECT * FROM t1 WHERE t1.a IN (SELECT a FROM t2);
Empty set (0.002 sec)
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 0 |
+--------------------------+
1 row in set (0.001 sec)
> SELECT @digests:=GROUP_CONCAT(plan_digest) FROM information_schema.statements_summary_history WHERE table_names LIKE '%test.t1%' AND stmt_type != 'CreateTable';
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| @digests:=GROUP_CONCAT(plan_digest) |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 73b2dec866595688ea416675f88ccb3456eb8e7443a79cd816695b688e07ac6b,8dc146249484f4a6ab219bfe9effa6b7a18aeed3764d49b610da61ac347ab914,c291edc36b2482738d3389d335f37efc76290be2930330fe5034c5f4c42eeb36,e72819cf99932f63a548156dbf433adda60e10337e89dcaa8638b4caf16f64d8 |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.001 sec)
> CREATE GLOBAL BINDING FROM HISTORY USING PLAN DIGEST @digests;
Query OK, 0 rows affected (0.060 sec)
> SHOW GLOBAL BINDINGS;
+----------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+-----------------+---------+------------------------------------------------------------------+------------------------------------------------------------------+
| Original_sql | Bind_sql | Default_db | Status | Create_time | Update_time | Charset | Collation | Source | Sql_digest | Plan_digest |
+----------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+-----------------+---------+------------------------------------------------------------------+------------------------------------------------------------------+
| insert into `test` . `t1` select * from `test` . `t2` where `a` = ? | INSERT INTO `test`.`t1` SELECT /*+ use_index(@`sel_1` `test`.`t2` `ia`) no_order_index(@`sel_1` `test`.`t2` `ia`)*/ * FROM `test`.`t2` WHERE `a` = 1 | test | enabled | 2024-08-11 05:27:19.669 | 2024-08-11 05:27:19.669 | utf8 | utf8_general_ci | history | bd23e6af17e7b77b25383e50e258f0dece18583d19772f08caacb2021945a300 | e72819cf99932f63a548156dbf433adda60e10337e89dcaa8638b4caf16f64d8 |
| update ( `test` . `t1` ) join `test` . `t2` set `t1` . `a` = ? where `t1` . `b` = `t2` . `a` | UPDATE /*+ inl_join(`test`.`t2`) use_index(@`upd_1` `test`.`t1` ) use_index(@`upd_1` `test`.`t2` `ia`) no_order_index(@`upd_1` `test`.`t2` `ia`)*/ (`test`.`t1`) JOIN `test`.`t2` SET `t1`.`a`=1 WHERE `t1`.`b` = `t2`.`a` | test | enabled | 2024-08-11 05:27:19.667 | 2024-08-11 05:27:19.667 | utf8 | utf8_general_ci | history | 987e91af17eb40e36fecfc0634cce0b6a736de02bb009091810f932804fc02e9 | c291edc36b2482738d3389d335f37efc76290be2930330fe5034c5f4c42eeb36 |
| delete `test` . `t1` from `test` . `t1` join `test` . `t2` where `t1` . `b` = `t2` . `a` | DELETE /*+ hash_join_build(`test`.`t2`) use_index(@`del_1` `test`.`t1` ) use_index(@`del_1` `test`.`t2` )*/ `test`.`t1` FROM `test`.`t1` JOIN `test`.`t2` WHERE `t1`.`b` = `t2`.`a` | test | enabled | 2024-08-11 05:27:19.664 | 2024-08-11 05:27:19.664 | utf8 | utf8_general_ci | history | 70ef3d442d95c51020a76c7c86a3ab674258606d4dd24bbd16ac6f69d87a4316 | 8dc146249484f4a6ab219bfe9effa6b7a18aeed3764d49b610da61ac347ab914 |
| select * from `test` . `t1` where `t1` . `a` in ( select `a` from `test` . `t2` ) | SELECT /*+ use_index(@`sel_1` `test`.`t1` ) stream_agg(@`sel_2`) use_index(@`sel_2` `test`.`t2` `ia`) order_index(@`sel_2` `test`.`t2` `ia`) agg_to_cop(@`sel_2`)*/ * FROM `test`.`t1` WHERE `t1`.`a` IN (SELECT `a` FROM `test`.`t2`) | test | enabled | 2024-08-11 05:27:19.649 | 2024-08-11 05:27:19.649 | utf8 | utf8_general_ci | history | b58508a5e29d7889adf98cad50343d7a575fd32ad55dbdaa88e14ecde54f3d93 | 73b2dec866595688ea416675f88ccb3456eb8e7443a79cd816695b688e07ac6b |
+----------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+-----------------+---------+------------------------------------------------------------------+------------------------------------------------------------------+
4 rows in set (0.001 sec)
> INSERT INTO t1 SELECT * FROM t2 WHERE a = 1;
Query OK, 0 rows affected (0.002 sec)
Records: 0 Duplicates: 0 Warnings: 0
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 1 |
+--------------------------+
1 row in set (0.000 sec)
> UPDATE t1, t2 SET t1.a = 1 WHERE t1.b = t2.a;
Query OK, 0 rows affected (0.002 sec)
Rows matched: 0 Changed: 0 Warnings: 0
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 1 |
+--------------------------+
1 row in set (0.000 sec)
> DELETE t1 FROM t1 JOIN t2 WHERE t1.b = t2.a;
Query OK, 0 rows affected (0.002 sec)
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 1 |
+--------------------------+
1 row in set (0.000 sec)
> SELECT * FROM t1 WHERE t1.a IN (SELECT a FROM t2);
Empty set (0.002 sec)
> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 1 |
+--------------------------+
1 row in set (0.002 sec)SQL 语句截断
当你使用 CREATE BINDING ... FROM HISTORY USING PLAN DIGEST 时，如果 语句概要表 中存储的该 digest 的 SQL 语句因长度超过 tidb_stmt_summary_max_sql_length 而被截断，则绑定可能会失败。此时，你需要增大 tidb_stmt_summary_max_sql_length。
权限
CREATE BINDING 语句需要 SUPER 权限。
MySQL 兼容性
该语句是 TiDB 对 MySQL 语法的扩展。