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Don Burleson Blog 







ORA-39726 Tips

Oracle Database Tips by Donald BurlesonAugust 10, 2015

Question:  I am getting ORA-39726 error when a dropping a column on a non-compressed table.  

ORA-39726:  unsupported add/drop column operation on compressed tables  

I am confused because I did not think that this table was compressed. 

What causes are there for the ORA-39726 error?

Answer:  In 11g and beyond, if you have a compressed table/column the following procedure will work to drop the column:

alter table compress for all operations;

alter table drop unused columns;

It is not possible to get the ORA-39726 error on a non-compressed table.

 However, Oracle has had several "types" of table compression over the years, including column-level compression.   

See here for details on Oracle table compression errors.  

The oerr utility shows this on the ORA-39726 error:  

ORA-39726:  unsupported add/drop column operation on compressed tables  

Cause:  An unsupported add/drop column operation for compressed table was attempted.  

Action:  When adding a column, do not specify a default value. DROP column is only supported in the form of SET UNUSED column (meta-data drop column).      

When dropping a column you can avoid the ORA-39726 error by setting the column to unused status:

  • alter table table_name set unused column column_name
  • alter table table_name drop unused columns

If you are using table compression, try moving the table into a non-compressed format:

  •  alter table table_name move nocompress;
  • alter table table_name drop column column_name;
  • alter table table_name compress;


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