5.5.5. Changing a Column's Default Value

5.5.5. Changing a Column's Default Value

5.5.5.改变列的默认值

To set a new default for a column, use a command like:

重设列的默认值，命令如下：

 

ALTER TABLE products ALTER COLUMN price SET DEFAULT 7.77;

 

Note that this doesn't affect any existing rows in the table, it just changes the default for future INSERT  commands.

请注意，这仅对新插入的数据有效，而对已有列不会产生影响。

 

To remove any default value, use:

删除默认值命令：

 

ALTER TABLE products ALTER COLUMN price DROP DEFAULT;

 

This is effectively the same as setting the default to null. As a consequence, it is not an error to drop  a default where one hadn't been defined, because the default is implicitly the null value.

这实际上与将默认值设置为null相同。所以，因为默认值隐式为空值，所以在没有定义默认值的地方删除默认值并不会抛出错误。