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DROP [GLOBAL|SESSION] BINDING
TiDB 数据库中 DROP [GLOBAL|SESSION] BINDING 的使用概况。
/docs-cn/dev/sql-statements/sql-statement-drop-binding/

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 ::=
    'DROP' GlobalScope 'BINDING' 'FOR' ( BindableStmt ( 'USING' BindableStmt )?
|   'SQL' 'DIGEST' StringLiteralOrUserVariableList )

GlobalScope ::=
    ( 'GLOBAL' | 'SESSION' )?

BindableStmt ::=
    ( SelectStmt | UpdateStmt | InsertIntoStmt | ReplaceIntoStmt | DeleteStmt )

StringLiteralOrUserVariableList ::=
    ( StringLitOrUserVariable | StringLiteralOrUserVariableList ',' StringLitOrUserVariable )

StringLiteralOrUserVariable ::=
    ( stringLiteral | UserVariable )

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。

{{< copyable "sql" >}}

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。

另请参阅