增加PostgreSQL中的多列序列

是否有任何内置方式(我的意思是,不需要触发器和/或函数)每个多列都有递增索引？

所以表演后：

INSERT INTO "table"
    ("month","desc")
    VALUES
    (1,'One thing'),(1,'Another thing'),'Last task of the month'),(2,(3,'First of third month')

我的表最终会像这样(注意“任务”列)：

month    task    desc
1        1       One thing
1        2       Another thing
1        3       Last task of the month
2        1       First of second month
2        2       Second and last of second month
3        1       First of third month

您可以将simlpe SERIAL列添加到您的表中(它将为您提供事物的顺序),然后使用以下内容：

SELECT *,row_number() OVER (PARTITION BY month ORDER BY serial_column)
FROM table

这将为您提供所需的结果.

如果您不需要订购行,可以尝试：

SELECT *,row_number() OVER (PARTITION BY month)
FROM table

详情：row_number() OVER(...)

UPD工作原理：

SERIAL类型的列本质上是“自动增量”字段.它会自动从序列中获取值.向表中插入行时,它们将如下所示：

| MONTH | SERIAL_COLUMN |                     DESCRIPTION |
-----------------------------------------------------------
|     1 |             1 |                       One thing |
|     1 |             2 |                   Another thing |
|     1 |             3 |          Last task of the month |
|     2 |             4 |           First of second month |
|     2 |             5 | Second and last of second month |
|     3 |             6 |            First of third month |

关键是 – 每个下一个添加的行的SERIAL_COLUMN值都大于以前的所有行.

下一个. row_number()OVER(PARTITION BY month ORDER BY serial_column)执行：

1)将所有行分成具有相同月份的组(PARTITION BY month)

2)按serial_column的值对它们进行排序(ORDER BY serial_column)

3)在每个组中使用步骤2中的排序分配行号(`row_number()OVER)

输出是：

| MONTH | SERIAL_COLUMN |                     DESCRIPTION | ROW_NUMBER |
------------------------------------------------------------------------
|     1 |             1 |                       One thing |          1 |
|     1 |             2 |                   Another thing |          2 |
|     1 |             3 |          Last task of the month |          3 |
|     2 |             4 |           First of second month |          1 |
|     2 |             5 | Second and last of second month |          2 |
|     3 |             6 |            First of third month |          1 |

要更改row_number()的输出,您需要更改SERIAL_COLUMN中的值.例如,将第二个月的第二个和最后一个月放在第二个月的第一个月之前,将改变SERIAL_COLUMN的值,如下所示：

UPDATE Table1
SET serial_column = 5
WHERE description = 'First of second month';

UPDATE Table1
SET serial_column = 4
WHERE description = 'Second and last of second month';

它将更改查询的输出：

| MONTH | SERIAL_COLUMN |                     DESCRIPTION | ROW_NUMBER |
------------------------------------------------------------------------
|     1 |             1 |                       One thing |          1 |
|     1 |             2 |                   Another thing |          2 |
|     1 |             3 |          Last task of the month |          3 |
|     2 |             4 | Second and last of second month |          1 |
|     2 |             5 |           First of second month |          2 |
|     3 |             6 |            First of third month |          1 |

SERIAL_COLUMN中的确切值无关紧要.他们只在一个月内就任务设定了订单.

我的sqlfiddle示例是here.

原文地址：https://www.jb51.cc/postgresql/191958.html

增加PostgreSQL中的多列序列

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