Question

我创建了一个存储过程，因为我希望有一个场景，我想从数据库中获取下一个数字。

DELIMITER $$
CREATE PROCEDURE `INCREMENT_IDENTIFIERS`(IN key_name varchar(30))
BEGIN
    SET @keyName := key_name;
    UPDATE APS_IDENTIFIERS SET COUNTER = COUNTER + 1 WHERE KEY_NAME = @keyName;
    SELECT * FROM APS_IDENTIFIERS WHERE KEY_NAME = @keyName;
END$$
DELIMITER ;

初始列值

调用存储过程后的最终列值

call INCREMENT_IDENTIFIERS('urn');

现在我的问题是，即使我传递了完全匹配的输入条件，这个存储过程为什么会增加两行，并且它会以增量值的形式返回两行作为输出。

Answer 1

没有必要使用9.4 User-Defined Variables，可以使用输入参数或13.6.4.1 Local Variable DECLARE Syntax：

mysql> DELIMITER //

mysql> CREATE PROCEDURE `INCREMENT_IDENTIFIERS`(
    ->   `in_key_name` VARCHAR(30)
    -> )
    -> BEGIN
    ->   UPDATE `APS_IDENTIFIERS`
    ->   SET `COUNTER` = `COUNTER` + 1
    ->   WHERE `KEY_NAME` = `in_key_name`;
    ->   SELECT `KEY_NAME`, `COUNTER`
    ->   FROM `APS_IDENTIFIERS`
    ->   WHERE `KEY_NAME` = `in_key_name`;
    -> END//
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> CALL `INCREMENT_IDENTIFIERS`('urn');
+----------+---------+
| KEY_NAME | COUNTER |
+----------+---------+
| urn      |       3 |
+----------+---------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

请参阅db-fiddle。

<强>更新

避免使用列名作为参数名称：

mysql> DELIMITER //

mysql> CREATE PROCEDURE `INCREMENT_IDENTIFIERS`(
    ->   `key_name` VARCHAR(30) -- CHANGE NAME
    -> )
    -> BEGIN
    ->   SET @`keyName` := `key_name`;
    ->   UPDATE `APS_IDENTIFIERS`
    ->   SET `COUNTER` = `COUNTER` + 1
    ->   WHERE `KEY_NAME` = @`keyName`;
    ->   SELECT `KEY_NAME`, `COUNTER`
    ->   FROM `APS_IDENTIFIERS`
    ->   WHERE `KEY_NAME` = @`keyName`;
    -> END//
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> CALL `INCREMENT_IDENTIFIERS`('urn');
+------------+---------+
| `KEY_NAME` | COUNTER |
+------------+---------+
| urn        |      69 |
| urn        |       3 |
+------------+---------+
2 rows in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

新参数名称：

mysql> DELIMITER //

mysql> CREATE PROCEDURE `INCREMENT_IDENTIFIERS`(
    ->   `_key_name` VARCHAR(30) -- NEW NAME
    -> )
    -> BEGIN
    ->   SET @`keyName` := `_key_name`;
    ->   UPDATE `APS_IDENTIFIERS`
    ->   SET `COUNTER` = `COUNTER` + 1
    ->   WHERE `KEY_NAME` = @`keyName`;
    ->   SELECT `KEY_NAME`, `COUNTER`
    ->   FROM `APS_IDENTIFIERS`
    ->   WHERE `KEY_NAME` = @`keyName`;
    -> END//
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> CALL `INCREMENT_IDENTIFIERS`('urn');
+----------+---------+
| KEY_NAME | COUNTER |
+----------+---------+
| urn      |       3 |
+----------+---------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

请参阅db-fiddle。

检查文档13.6.4.2 Local Variable Scope and Resolution。

更新2

另一个选项（不太推荐）是使用合格的列名（APS_IDENTIFIERS.KEY_NAME）：

mysql> DELIMITER //

mysql> CREATE PROCEDURE `INCREMENT_IDENTIFIERS`(
    ->   `key_name` VARCHAR(30)
    -> )
    -> BEGIN
    ->   SET @`keyName` := `key_name`;
    ->   UPDATE `APS_IDENTIFIERS`
    ->   SET `COUNTER` = `COUNTER` + 1
    ->   WHERE `APS_IDENTIFIERS`.`KEY_NAME` = @`keyName`;
    ->   SELECT `KEY_NAME`, `COUNTER`
    ->   FROM `APS_IDENTIFIERS`
    ->   WHERE `APS_IDENTIFIERS`.`KEY_NAME` = @`keyName`;
    -> END//
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> CALL `INCREMENT_IDENTIFIERS`('urn');
+------------+---------+
| `KEY_NAME` | COUNTER |
+------------+---------+
| urn        |       3 |
+------------+---------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

请参阅db-fiddle。

检查文档9.2.1 Identifier Qualifiers。

mysql存储过程不一致地增加所有记录

1 个答案: