database Oracle：将 VARCHAR2 列更改为 CLOB
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Oracle: Changing VARCHAR2 column to CLOB
提问by Maccath
I have an encountered an issue where the data I was trying to store in my varchar2(4000) column was too big, so I wish to change the column to one more suitable for storing large amounts of textual data. Specifically, a serialized array.
我遇到了一个问题，我试图在 varchar2(4000) 列中存储的数据太大，因此我希望将该列更改为更适合存储大量文本数据的列。具体来说，一个序列化的数组。
Firstly, is CLOB the best data type for me to use for this purpose? Is there a more appropriate data type?
Secondly, when I try to alter the column using the usual snyntax:
ALTER TABLE table MODIFY column CLOBI get the following error: ORA-22858: invalid alteration of datatype
What's the most straightforward way to alter this table without losing any data?
首先，CLOB 是我为此目的使用的最佳数据类型吗？有没有更合适的数据类型？
其次，当我尝试使用通常的语法更改列时：
ALTER TABLE table MODIFY column CLOB我收到以下错误：ORA-22858：数据类型的无效更改
在不丢失任何数据的情况下更改此表的最直接方法是什么？
回答by a_horse_with_no_name
The most straightforward way, given that the operation of moving from a varcharcolumn to a CLOBis disallowed, would be to create a new column and move the data from the old column to the new column:
考虑varchar到CLOB不允许从列移动到 a 的操作，最直接的方法是创建一个新列并将数据从旧列移动到新列：
ALTER TABLE some_table ADD (foo CLOB);
UPDATE some_table SET foo = old_column;
ALTER TABLE some_table DROP COLUMN old_column;
ALTER TABLE some_table RENAME COLUMN foo TO old_column;
回答by Ausaf
The VARCHAR2 column cannot be directly converted to CLOB but it can be done in 2 steps:
VARCHAR2 列不能直接转换为 CLOB，但可以分两步完成：
- Convert column datatype from VARCHAR2 to LONG.
- Convert column datatype from LONG to CLOB.
- 将列数据类型从 VARCHAR2 转换为 LONG。
- 将列数据类型从 LONG 转换为 CLOB。
ALTER TABLE table MODIFY column long;
ALTER TABLE table MODIFY column clob;
回答by user11815390
For Oracle 11g:
对于 Oracle 11g：
ALTER TABLE table MODIFY column long;
ALTER TABLE table MODIFY column clob;
