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

1. DropBindingStmt ::=
2. 'DROP' GlobalScope 'BINDING' 'FOR' BindableStmt ( 'USING' BindableStmt )?

4. GlobalScope ::=
5. ( 'GLOBAL' | 'SESSION' )?

7. BindableStmt ::=
8. ( SelectStmt | UpdateStmt | InsertIntoStmt | ReplaceIntoStmt | DeleteStmt )

示例

1. CREATE TABLE t1 (
2. ->  id INT NOT NULL PRIMARY KEY auto_increment,
3. ->  b INT NOT NULL,
4. ->  pad VARBINARY(255),
5. ->  INDEX(b)
6. -> );
7. Query OK, 0 rows affected (0.07 sec)

9. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM dual;
10. Query OK, 1 row affected (0.01 sec)
11. Records: 1  Duplicates: 0  Warnings: 0

13. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
14. Query OK, 1 row affected (0.00 sec)
15. Records: 1  Duplicates: 0  Warnings: 0

17. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
18. Query OK, 8 rows affected (0.00 sec)
19. Records: 8  Duplicates: 0  Warnings: 0

21. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
22. Query OK, 1000 rows affected (0.04 sec)
23. Records: 1000  Duplicates: 0  Warnings: 0

25. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
26. Query OK, 100000 rows affected (1.74 sec)
27. Records: 100000  Duplicates: 0  Warnings: 0

29. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
30. Query OK, 100000 rows affected (2.15 sec)
31. Records: 100000  Duplicates: 0  Warnings: 0

33. INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
34. Query OK, 100000 rows affected (2.64 sec)
35. Records: 100000  Duplicates: 0  Warnings: 0

37. SELECT SLEEP(1);
38. +----------+
39. | SLEEP(1) |
40. +----------+
41. |        0 |
42. +----------+
43. 1 row in set (1.00 sec)

45. ANALYZE TABLE t1;
46. Query OK, 0 rows affected (1.33 sec)

48. EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
49. +-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
50. | id                            | estRows | actRows | task      | access object        | execution info                                                            | operator info                     | memory         | disk |
51. +-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
52. | 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  |
53. | ├─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  |
54. | └─TableRowIDScan_9(Probe)     | 583.00  | 297     | cop[tikv] | table:t1             | time:12ms, loops:4                                                        | keep order:false                  | N/A            | N/A  |
55. +-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
56. 3 rows in set (0.02 sec)

58. CREATE SESSION BINDING FOR
59. ->  SELECT * FROM t1 WHERE b = 123
60. -> USING
61. ->  SELECT * FROM t1 IGNORE INDEX (b) WHERE b = 123;
62. Query OK, 0 rows affected (0.00 sec)

64. EXPLAIN ANALYZE  SELECT * FROM t1 WHERE b = 123;
65. +-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
66. | id                      | estRows   | actRows | task      | access object | execution info                                                                 | operator info      | memory        | disk |
67. +-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
68. | 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  |
69. | └─Selection_6           | 583.00    | 297     | cop[tikv] |               | time:224ms, loops:298                                                          | eq(test.t1.b, 123) | N/A           | N/A  |
70. |   └─TableFullScan_5     | 301010.00 | 301010  | cop[tikv] | table:t1      | time:220ms, loops:298                                                          | keep order:false   | N/A           | N/A  |
71. +-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
72. 3 rows in set (0.22 sec)

74. SHOW SESSION BINDINGS\G
75. *************************** 1. row ***************************
76. Original_sql: select * from t1 where b = ?
77. Bind_sql: SELECT * FROM t1 IGNORE INDEX (b) WHERE b = 123
78. Default_db: test
79. Status: using
80. Create_time: 2020-05-22 14:38:03.456
81. Update_time: 2020-05-22 14:38:03.456
82. Charset: utf8mb4
83. Collation: utf8mb4_0900_ai_ci
84. 1 row in set (0.00 sec)

86. DROP SESSION BINDING FOR SELECT * FROM t1 WHERE b = 123;
87. Query OK, 0 rows affected (0.00 sec)

89. EXPLAIN ANALYZE  SELECT * FROM t1 WHERE b = 123;
90. +-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
91. | id                            | estRows | actRows | task      | access object        | execution info                                                          | operator info                     | memory         | disk |
92. +-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
93. | 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  |
94. | ├─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  |
95. | └─TableRowIDScan_9(Probe)     | 583.00  | 297     | cop[tikv] | table:t1             | time:0s, loops:4                                                        | keep order:false                  | N/A            | N/A  |
96. +-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
97. 3 rows in set (0.01 sec)

99. SHOW SESSION BINDINGS\G
100. Empty set (0.00 sec)

MySQL 兼容性

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

另请参阅