Question

这是我的表

jobs (
  depaermentid,
  empid,
  department
)

我插入了属于同一部门的空值

我喜欢检索值而不是null属于同一部门的其他值

1|1|
1|2|it
2|1|
2|2|cs

结果喜欢

1|1|it
1|2|it

我试过了这个查询

select gepartmentid,empId,department from from jobs group bt department;

Answer 1

尝试：

mysql> DROP TABLE IF EXISTS `jobs`;
Query OK, 0 rows affected (0.01 sec)

mysql> CREATE TABLE IF NOT EXISTS `jobs` (
    ->   `depaermentid` TINYINT NOT NULL,
    ->   `empid` TINYINT NOT NULL,
    ->   `department` CHAR(2)
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO `jobs` (
    ->   `depaermentid`,
    ->   `empid`,
    ->   `department`
    -> ) VALUES
    ->   (1, 1, NULL),
    ->   (1, 2, 'it'),
    ->   (2, 1, NULL),
    ->   (2, 2, 'cs');
Query OK, 4 rows affected (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT
    ->   `jobs`.`depaermentid`,
    ->   `jobs`.`empid`,
    ->   IFNULL(`jobs`.`department`, `der`.`department`) `department`
    -> FROM
    ->   `jobs`
    ->   INNER JOIN (
    ->     SELECT
    ->       `depaermentid`,
    ->       `department`
    ->     FROM
    ->       `jobs`
    ->     WHERE
    ->       `department` IS NOT NULL  
    ->   ) `der` ON `jobs`.`depaermentid` = `der`.`depaermentid`;
+--------------+-------+------------+
| depaermentid | empid | department |
+--------------+-------+------------+
|            1 |     1 | it         |
|            1 |     2 | it         |
|            2 |     1 | cs         |
|            2 |     2 | cs         |
+--------------+-------+------------+
4 rows in set (0.00 sec)

请参阅db-fiddle。

如何在同一个表的同一个字段中将null值与其他值连接起来

1 个答案: