Question

使用GROUP_CONCAT在mysql中创建了一个新函数。我的功能如下：

    CREATE  FUNCTION `Get_customerCodes`(customer_id int(11)) 
    RETURNS varchar(500) CHARSET utf8
    BEGIN
    Declare Result VARCHAR(1000);
        set Result =  (select GROUP_CONCAT(concat('\'', customer_code,'\'') 
              SEPARATOR ',') from customers 
         where customer_id in (customer_id));
   Return Result;
   END

当我调用上面的函数时，它会返回这样的逗号分隔的客户代码＆＃39; 1＆＃39;＆＃39 2＆＃39;＆＃39 3＆＃39;＆＃39; 4＆＃39;

但是我需要在 IN 条件的where子句中使用输出 Get_customerCodes 函数。

测试用例：

 select * from my_table where customer_code IN (Get_customerCodes(CAST('1002' AS SIGNED)));

期望：

在执行上述查询时，mysql应该根据函数输出给出结果。实际查询看起来像下面

从my_table中选择*，其中customer_code为IN（＆＃39; 1＆＃39;，＆＃39; 2＆＃39;，＆＃39; 3＆＃39;，＆＃39; 4＆＃39;） ;

问题：

是否可以使用mysql函数输出作为其中的一部分条件 IN 条款。
如果可能的话，提供一个例子。如果不可能给我一个替代方案溶液

Answer 1

要考虑的几点：

The result is truncated to the maximum length that is given by the group_concat_max_len system variable,，请参阅12.19.1 Aggregate (GROUP BY) Function Descriptions :: GROUP_CONCAT。
避免将函数的参数命名为表的列，请参阅C.1 Restrictions on Stored Programs :: Name Conflicts within Stored Routines。

使用13.5 Prepared SQL Statement Syntax的选项：

mysql> DROP TABLE IF EXISTS `my_table`, `customers`;
Query OK, 0 rows affected (0.00 sec)

mysql> DROP FUNCTION IF EXISTS `Get_customerCodes`;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE IF NOT EXISTS `customers`(
    ->   `customer_id` INT NOT NULL,
    ->   `customer_code` VARCHAR(2),
    ->   PRIMARY KEY(`customer_id`, `customer_code`)
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE IF NOT EXISTS `my_table`(
    ->   `id` INT NOT NULL,
    ->   `customer_code` VARCHAR(2)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> CREATE FUNCTION `Get_customerCodes`(`_customer_id` INT)
    -> RETURNS VARCHAR(500) CHARSET utf8
    ->   RETURN (
    ->     SELECT GROUP_CONCAT(CONCAT('\'', `customer_code`, '\'')
    ->            SEPARATOR ',')
    ->     FROM `customers`
    ->     WHERE `customer_id` IN (`_customer_id`)
    ->   );
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO `customers`
    ->   (`customer_id`, `customer_code`)
    -> VALUES
    ->   (1002, 1), (1002, 2),
    ->   (1002, 3), (1002, 4);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> INSERT INTO `my_table`
    ->   (`id`, `customer_code`)
    -> VALUES
    ->   (1, 1), (2, 2),
    ->   (3, 3), (4, 4);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SET @`query` := CONCAT('
    '> SELECT *
    '> FROM `my_table`
    '> WHERE `customer_code` IN (',
    -> `Get_customerCodes`(CAST('1002' AS SIGNED)), ')');
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @`query` `to_execute`;
+----------------------------------------------------------------------+
| to_execute                                                           |
+----------------------------------------------------------------------+
| 
SELECT *
FROM `my_table`
WHERE `customer_code` IN ('1','2','3','4') |
+----------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> PREPARE `stmt` FROM @`query`;
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> EXECUTE `stmt`;
+----+---------------+
| id | customer_code |
+----+---------------+
|  1 | 1             |
|  2 | 2             |
|  3 | 3             |
|  4 | 4             |
+----+---------------+
4 rows in set (0.00 sec)

mysql> DEALLOCATE PREPARE `stmt`;
Query OK, 0 rows affected (0.00 sec)

请参阅db-fiddle。

Answer 2

我遇到了类似的问题，并在FIND_IN_SET的帮助下得以解决：

SELECT * FROM my_table WHERE FIND_IN_SET(customer_code, Get_customerCodes(1002));

Mysql函数输出作为where子句的一部分

2 个答案: