如何将varchar2修改为clob类型字段(使用long过渡)

直接从varchar2 修改为clob会报错，不让修改，可以先修改为Long类型，然后从Long修改为clob .

而且更改为long，必须是 ORA-01439: 要修改的資料欄必須是空的, 才可以變更資料庫

Using ALTER TABLE to Convert LONG Columns to LOB Columns

You can use the ALTER TABLE statement in SQL to convert a LONG column to a LOB column. To do so, use the following syntax:

For example, if you had a table that was created as follows:

then you can change the column long_col in table Long_tab to datatype CLOB using following ALTER TABLE statement:

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