在 DB2 中减少列长度的方法

Question

Is there a way to decrease the column length in DB2?

Say I have a table temp with column col1 defined as VARCHAR(80) . I want to reduce it to VARCHAR(60) .

Answer 1

In DB2 9.7 for Linux/UNIX/Windows, you can use the ALTER TABLE statement to reduce the length of a column, assuming that no values in the column exceed the new column size :

ALTER TABLE temp
    ALTER COLUMN col1 SET DATA TYPE VARCHAR(60);

If any values in the column exceed the desired size you must handle that first.

In previous versions of DB2 for Linux/UNIX/Windows, you could not utilize this method to reduce the size of the column. You either had to drop/recreate the table, or go through a process of adding a column, copying data, and removing the old column.

Answer 2

As an addition to Ian's answer and Clockwork-Muse's remark :

While it is possible, as Ian pointed out, to use ALTER statements to reduce column length in DB for LUW, this is not the case in DB2 for z/OS as of version 10.

According to this table , only data type changes from VARCHAR(n) to VARCHAR(n+x) are supported, which is a bummer.

Answer 3

You cannot reduce the length of a column. To achieve this affect you should

• create a new table with your data and with the attribute that you want.
• Delete old table
• Rename the new table

If you want to increase the length, it is possible with ALTER command

 ALTER TABLE temp
      ALTER COLUMN col1
      SET DATA TYPE VARCHAR(60)