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' SqlDigest)

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

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

示例

你可以根据 SQL 语句或 sql_digest 删除绑定。

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。

mysql> CREATE TABLE t(id INT PRIMARY KEY , a INT, KEY(a));
Query OK, 0 rows affected (0.06 sec)

mysql> SELECT /*+ IGNORE_INDEX(t, a) */ * FROM t WHERE a = 1;
Empty set (0.01 sec)

mysql> SELECT plan_digest FROM INFORMATION_SCHEMA.STATEMENTS_SUMMARY WHERE QUERY_SAMPLE_TEXT = 'SELECT /*+ IGNORE_INDEX(t, a) */ * FROM t WHERE a = 1';
+------------------------------------------------------------------+
| plan_digest                                                      |
+------------------------------------------------------------------+
| 4e3159169cc63c14b139a4e7d72eae1759875c9a9581f94bb2079aae961189cb |
+------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> CREATE BINDING FROM HISTORY USING PLAN DIGEST '4e3159169cc63c14b139a4e7d72eae1759875c9a9581f94bb2079aae961189cb';
Query OK, 0 rows affected (0.02 sec)

mysql> SELECT * FROM t WHERE a = 1;
Empty set (0.01 sec)

mysql> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
|                        1 |
+--------------------------+
1 row in set (0.01 sec)

mysql> SHOW BINDINGS\G;
*************************** 1. row ***************************
Original_sql: select * from `test` . `t` where `a` = ?
    Bind_sql: SELECT /*+ use_index(@`sel_1` `test`.`t` ) ignore_index(`t` `a`)*/ * FROM `test`.`t` WHERE `a` = 1
  Default_db: test
      Status: enabled
 Create_time: 2022-12-14 15:26:22.277
 Update_time: 2022-12-14 15:26:22.277
     Charset: utf8mb4
   Collation: utf8mb4_general_ci
      Source: history
  Sql_digest: 6909a1bbce5f64ade0a532d7058dd77b6ad5d5068aee22a531304280de48349f
 Plan_digest: 4e3159169cc63c14b139a4e7d72eae1759875c9a9581f94bb2079aae961189cb
1 row in set (0.02 sec)

ERROR:
No query specified

mysql> DROP BINDING FOR SQL DIGEST '6909a1bbce5f64ade0a532d7058dd77b6ad5d5068aee22a531304280de48349f';
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW BINDINGS\G;
Empty set (0.01 sec)

ERROR:
No query specified

MySQL 兼容性

DROP [GLOBAL|SESSION] BINDING 语句是 TiDB 对 MySQL 语法的扩展。

另请参阅

CREATE [GLOBAL|SESSION] BINDING
SHOW [GLOBAL|SESSION] BINDINGS
ANALYZE
Optimizer Hints
执行计划管理 (SPM)

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sql-statement-drop-binding.md

sql-statement-drop-binding.md

DROP [GLOBAL|SESSION] BINDING

语法图

示例

MySQL 兼容性

另请参阅

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DROP [GLOBAL|SESSION] BINDING

语法图

示例

MySQL 兼容性

另请参阅