DROP [GLOBAL|SESSION] BINDING
DROP BINDING 语句用于删除指定的 SQL 绑定。绑定可用于将优化器 Hint 插入语句中，而无需更改底层查询。
BINDING 语句可以在 GLOBAL 或者 SESSION 作用域内删除执行计划绑定。在不指定作用域时，默认的作用域为 SESSION。
语法图
- DropBindingStmt
- GlobalScope
- BindableStmt
- StringLiteralOrUserVariableList
- StringLiteralOrUserVariable
示例
你可以根据 SQL 语句或 SQL Digest 删除绑定。
根据 SQL Digest 删除绑定时，你需要指定相应的 SQL Digest：
- 既可以通过字符串字面量来指定，也可以通过字符串类型的用户变量来指定。
- 可以指定多个字符串，同时每个字符串也可以包含多个 digest，注意字符串之间和 digest 之间均需使用逗号隔开。
下面的示例演示如何根据 SQL 语句删除绑定。
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)
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
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
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
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
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
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
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
SELECT SLEEP(1);
+----------+
| SLEEP(1) |
+----------+
| 0 |
+----------+
1 row in set (1.00 sec)
ANALYZE TABLE t1;
Query OK, 0 rows affected (1.33 sec)
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)
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)
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)
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)
DROP SESSION BINDING FOR SELECT * FROM t1 WHERE b = 123;
Query OK, 0 rows affected (0.00 sec)
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)
SHOW SESSION BINDINGS\G
Empty set (0.00 sec)下面的示例演示如何根据 SQL Digest 删除绑定。
CREATE TABLE t1(a INT, b INT, c INT, INDEX ia(a));
CREATE TABLE t2(a INT, b INT, c INT, INDEX ia(a));
CREATE GLOBAL BINDING FOR SELECT * FROM t1 WHERE a > 1 USING SELECT * FROM t1 USE INDEX (ia) WHERE a > 1;
CREATE GLOBAL BINDING FOR SELECT * FROM t2 WHERE a < 1 USING SELECT * FROM t2 USE INDEX (ia) WHERE a < 1;
CREATE GLOBAL BINDING FOR SELECT * FROM t1 JOIN t2 ON t1.b = t2.a USING SELECT /*+ HASH_JOIN(t1) */ * FROM t1 JOIN t2 ON t1.b = t2.a;
SHOW GLOBAL BINDINGS;方法一：
DROP GLOBAL BINDING FOR SQL DIGEST '31026623c8f22264fe0dfc26f29c69c5c457d6b85960c578ebcf17a967ed7893', '0f38b2e769927ae37981c66f0988c6299b602e03f029e38aa071e656fc321593', '3c8dfc451b0e36afd904cefca5137e68fb051f02964e1958ed60afdadc25f57e';
SHOW GLOBAL BINDINGS;方法二：
SET @digests='31026623c8f22264fe0dfc26f29c69c5c457d6b85960c578ebcf17a967ed7893, 0f38b2e769927ae37981c66f0988c6299b602e03f029e38aa071e656fc321593, 3c8dfc451b0e36afd904cefca5137e68fb051f02964e1958ed60afdadc25f57e';
DROP GLOBAL BINDING FOR SQL DIGEST @digests;
SHOW GLOBAL BINDINGS;> CREATE TABLE t1(a INT, b INT, c INT, INDEX ia(a));
Query OK, 0 rows affected (0.044 sec)
> CREATE TABLE t2(a INT, b INT, c INT, INDEX ia(a));
Query OK, 0 rows affected (0.035 sec)
> CREATE GLOBAL BINDING FOR SELECT * FROM t1 WHERE a > 1 USING SELECT * FROM t1 USE INDEX (ia) WHERE a > 1;
Query OK, 0 rows affected (0.011 sec)
> CREATE GLOBAL BINDING FOR SELECT * FROM t2 WHERE a < 1 USING SELECT * FROM t2 USE INDEX (ia) WHERE a < 1;
Query OK, 0 rows affected (0.013 sec)
> CREATE GLOBAL BINDING FOR SELECT * FROM t1 JOIN t2 ON t1.b = t2.a USING SELECT /*+ HASH_JOIN(t1) */ * FROM t1 JOIN t2 ON t1.b = t2.a;
Query OK, 0 rows affected (0.012 sec)
> SHOW GLOBAL BINDINGS;
+---------------------------------------------------------------------------+-----------------------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+-----------------+--------+------------------------------------------------------------------+-------------+
| Original_sql | Bind_sql | Default_db | Status | Create_time | Update_time | Charset | Collation | Source | Sql_digest | Plan_digest |
+---------------------------------------------------------------------------+-----------------------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+-----------------+--------+------------------------------------------------------------------+-------------+
| select * from `test` . `t1` join `test` . `t2` on `t1` . `b` = `t2` . `a` | SELECT /*+ HASH_JOIN(`t1`)*/ * FROM `test`.`t1` JOIN `test`.`t2` ON `t1`.`b` = `t2`.`a` | test | enabled | 2024-08-11 04:06:49.953 | 2024-08-11 04:06:49.953 | utf8 | utf8_general_ci | manual | 31026623c8f22264fe0dfc26f29c69c5c457d6b85960c578ebcf17a967ed7893 | |
| select * from `test` . `t2` where `a` < ? | SELECT * FROM `test`.`t2` USE INDEX (`ia`) WHERE `a` < 1 | test | enabled | 2024-08-11 04:06:49.937 | 2024-08-11 04:06:49.937 | utf8 | utf8_general_ci | manual | 0f38b2e769927ae37981c66f0988c6299b602e03f029e38aa071e656fc321593 | |
| select * from `test` . `t1` where `a` > ? | SELECT * FROM `test`.`t1` USE INDEX (`ia`) WHERE `a` > 1 | test | enabled | 2024-08-11 04:06:49.924 | 2024-08-11 04:06:49.924 | utf8 | utf8_general_ci | manual | 3c8dfc451b0e36afd904cefca5137e68fb051f02964e1958ed60afdadc25f57e | |
+---------------------------------------------------------------------------+-----------------------------------------------------------------------------------------+------------+---------+-------------------------+-------------------------+---------+-----------------+--------+------------------------------------------------------------------+-------------+
3 rows in set (0.001 sec)
> DROP GLOBAL BINDING FOR SQL DIGEST '31026623c8f22264fe0dfc26f29c69c5c457d6b85960c578ebcf17a967ed7893', '0f38b2e769927ae37981c66f0988c6299b602e03f029e38aa071e656fc321593', '3c8dfc451b0e36afd904cefca5137e68fb051f02964e1958ed60afdadc25f57e';
Query OK, 3 rows affected (0.019 sec)
> SHOW GLOBAL BINDINGS;
Empty set (0.002 sec)MySQL 兼容性
DROP [GLOBAL|SESSION] BINDING 语句是 TiDB 对 MySQL 语法的扩展。