英文:
Will there be any effect if I change the varchar2 column size?
问题
我有一张表，几乎有20列，至少有十亿行。
如果我将其中一列的类型从varchar2(8)更改为varchar2(16)会怎么样？给定列上没有索引、约束或外键。但是我的表中有太多的记录。我将使用下面的脚本进行操作：
ALTER TABLE user MODIFY type VARCHAR2(16);
我已经在我的测试环境中执行了这个操作，但它的记录数没有我的生产环境多。
英文:
I have a table with almost 20 columns and at least one billion rows.
What if I change type of one column from varchar2(8) to varchar2(16)? There is no index, constraint or foreign key on given column. But my table has too many records. I will use below script for the operation:
ALTER TABLE user MODIFY type VARCHAR2(16);
I have done this operation in my test environment but it does not have as many records as my production environment.
答案1
得分: 2
根据我所了解，这将会是立即的。这是一个varchar2列，更改仅在数据字典中进行，表数据不受任何影响。
如果是char的话，是的 - 这将需要时间，因为这样的列包含的数据会在右侧用空格填充到其完整长度，所以您实际上需要扩大列的大小，还要在表上执行更新操作，如果有很多行，那会花费时间。
英文:
As far as I can tell, it'll be instantly. It is a varchar2 column and change is being done only in data dictionary, table data isn't affected at all.
If it were char, then yes - it would take time because such a column contains data right-padded with spaces up to its full length, so you'd actually have to enlarge the column, but also perform update on a table, and that would take time if there are that many rows.
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