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DROP [GLOBAL|SESSION] BINDING

This statement removes a binding from a specific SQL statement. Bindings can be used to inject a hint into a statement without requiring changes to the underlying query.

A BINDING can be on either a GLOBAL or SESSION basis. The default is SESSION.

Synopsis

DropBindingStmt:

DropBindingStmt

GlobalScope:

GlobalScope

SelectStmt

SelectStmt

Syntax description

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)

mysql> SHOW SESSION BINDINGS\G
Empty set (0.00 sec)

MySQL compatibility

This statement is a TiDB extension to MySQL syntax.

See also