Java MySQL-仅从列中选择默认值

我想知道是否可以只选择空列的默认值？ 我有一个绝对空的表，我只想选择默认值中的一列——这对我的JAVA应用程序很重要，它正在填充表

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谢谢。

我只能想到两种方法：

插入一行

插入一行，但不指定该列的值

从该行中选择列；它将具有该列的默认值

删除该行

…可能都在一个事务中，所以其他人看不到它

使用

描述

（

解释

）

descripe

命令（aka）描述系统中的对象，包括表。因此，如果您对表进行

解释

，您将获得有关该表的信息，包括其默认值

以下是链接文档中的一个示例：

mysql> DESCRIBE City; +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ | Field | Type | Null | Key | Default | Extra | +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ | Id | int(11) | NO | PRI | NULL | auto_increment | | Name | char(35) | NO | | | | | Country | char(3) | NO | UNI | | | | District | char(20) | YES | MUL | | | | Population | int(11) | NO | | 0 | | +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ mysql>描述城市； +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ |字段|类型|空|键|默认|额外| +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ |Id | int（11）| NO | PRI | NULL |自动增量| |姓名| char（35）|否| | || |国家| char（3）| NO | UNI || |地区|查尔（20）|是|穆尔|| |人口|国际（11）|否| 0 || +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ 因此，您可以从返回行的

default

列中提取默认值

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啊，当然，还有第三种方法，请参见。

您可以从INFORMATION\u SCHEMA.COLUMNS获取默认值

select COLUMN_DEFAULT
from INFORMATION_SCHEMA.COLUMNS 
where TABLE_SCHEMA='your_db' and TABLE_NAME='your_table' and COLUMN_NAME='your_column'

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如果您只想让MySQL自动插入表，则可以在创建表时为列定义默认值：

create table my_table (i INT DEFAULT 1);

但是，如果您的意思是想要存储在DB dictionary中的默认值，则可以通过以下查询获得：

SELECT Column_Default
  FROM Information_Schema.Columns
WHERE Table_Schema = 'yourSchema'
  AND Table_Name = 'yourTableName'
  AND Column_Name = 'yourColumnName'

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啊，出于某种原因，我倾向于忘记

信息\u模式

，这是第三种（或者可能是第一种）方式。：-）Codd第4条规则；）