MySQL触发器中的持久/静态变量

我在黑洞表上有以下触发器，它截取插入并将它们传递给其他表。
为了加快速度，我想计算一个递增的值，并将其传递到插入中

DELIMITER $$

CREATE TRIGGER ai_blackhole_each AFTER INSERT ON `test.blackhole` FOR EACH ROW
BEGIN
  DECLARE calculated_id INTEGER;

  SET calculated_id = calc_id_for_previous_insert + 1;
  INSERT INTO example VALUES(new.field1, new.field2, calculated_id, ..);
END$$

DELIMITER ;

触发器中是否可以有一个静态变量，在触发之间保持其值？

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或者有什么技巧可以有效地实现这样的效果吗？

在内存表中从0开始放置一个间歇值

use test
DROP TABLE IF EXISTS test.blackholecounter;
DROP TABLE IF EXISTS test.blackhole;
DROP TABLE IF EXISTS test.example;
CREATE TABLE test.blackholecounter (calc_id INT NOT NULL DEFAULT 0) ENGINE=MEMORY;
INSERT INTO test.blackholecounter VALUES (0);
CREATE TABLE test.blackhole
(
    field1 VARCHAR(20),
    field2 VARCHAR(20)
) ENGINE=BLACKHOLE;
CREATE TABLE test.example (field1 VARCHAR(20),
field2 VARCHAR(20),
calc_id INT);
DELIMITER $$
CREATE TRIGGER ai_blackhole_each AFTER INSERT ON test.blackhole
FOR EACH ROW
BEGIN
    DECLARE calculated_id INTEGER;
    SELECT calc_id INTO calculated_id FROM test.blackholecounter;
    UPDATE test.blackholecounter SET calc_id=calc_id+1;
    INSERT INTO test.example VALUES(new.field1, new.field2, calculated_id);
END
$$
DELIMITER ;
SELECT * FROM test.blackholecounter;
SELECT * FROM test.example;
INSERT INTO test.blackhole (field1,field2) VALUES ('rolando','edwards'),('pamela','edwards');
SELECT * FROM test.blackholecounter;
SELECT * FROM test.example;

这是我将其粘贴到MySQL中时得到的结果

mysql> use test
Database changed
mysql> DROP TABLE IF EXISTS test.blackholecounter;
Query OK, 0 rows affected (0.00 sec)

mysql> DROP TABLE IF EXISTS test.blackhole;
Query OK, 0 rows affected (0.01 sec)

mysql> DROP TABLE IF EXISTS test.example;
Query OK, 0 rows affected (0.06 sec)

mysql> CREATE TABLE test.blackholecounter (calc_id INT NOT NULL DEFAULT 0) ENGINE=MEMORY;
Query OK, 0 rows affected (0.05 sec)

mysql> INSERT INTO test.blackholecounter VALUES (0);
Query OK, 1 row affected (0.00 sec)

mysql> CREATE TABLE test.blackhole(field1 VARCHAR(20),field2 VARCHAR(20)) ENGINE=BLACKHOLE;
Query OK, 0 rows affected (0.06 sec)

mysql> CREATE TABLE test.example (field1 VARCHAR(20),field2 VARCHAR(20),calc_id INT);
Query OK, 0 rows affected (0.09 sec)

mysql> DELIMITER $$
mysql> CREATE TRIGGER ai_blackhole_each AFTER INSERT ON test.blackhole
    -> FOR EACH ROW
    -> BEGIN
    ->     DECLARE calculated_id INTEGER;
    ->     SELECT calc_id INTO calculated_id FROM test.blackholecounter;
    ->     UPDATE test.blackholecounter SET calc_id=calc_id+1;
    ->     INSERT INTO test.example VALUES(new.field1, new.field2, calculated_id);
    -> END
    -> $$
Query OK, 0 rows affected (0.11 sec)

mysql> DELIMITER ;
mysql> SELECT * FROM test.blackholecounter;
+---------+
| calc_id |
+---------+
|       0 |
+---------+
1 row in set (0.00 sec)

mysql> SELECT * FROM test.example;
Empty set (0.02 sec)

mysql> INSERT INTO test.blackhole (field1,field2) VALUES ('rolando','edwards'),('pamela','edwards');
Query OK, 2 rows affected (0.07 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM test.blackholecounter;
+---------+
| calc_id |
+---------+
|       2 |
+---------+
1 row in set (0.00 sec)

mysql> SELECT * FROM test.example;
+---------+---------+---------+
| field1  | field2  | calc_id |
+---------+---------+---------+
| rolando | edwards |       0 |
| pamela  | edwards |       1 |
+---------+---------+---------+
2 rows in set (0.00 sec)

您可以在test.blackholecounter表中使用其他数字开始初始值，或者在触发器中发生增量时更改顺序

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试试看

表中的一行如何（如果不需要持久性，引擎=内存）？@konerak，这是一个黑客攻击，但它可以工作。