Rules and Restrictions for Large Object Data Types
Teradata Database supports the following large object (LOB) data types.
The rules for specifying these types in an ALTER TABLE request are different from the rules that apply to other data types. Rules for specifying LOB data types in an ALTER TABLE request are as follows.
To increase the maximum size for a BLOB or CLOB column definition, use the ADD column_name option, specify the name of the column whose LOB data type you want to increase, and Teradata Database modifies the size of the type to the value you specify. For example, suppose you want to double the maximum size of a CLOB column named standard_error in the table named performance_data from 524,288,000 characters to 1,048,576,000 characters. You can use the following ALTER TABLE request to increase the size of the CLOB data type for standard_error to 1,048,576,000 characters.
ALTER TABLE performance_data
ADD standard_error CLOB(1048576000);
Note: Teradata Database knows that column standard_error already exists in performance_data, so it interprets the ADD option to mean that standard_error is to be modified, not added.
You cannot change the attribute from NULL to NOT NULL if there are nulls in any rows in the table for that column.
If you change the tdlocaledef.txt file and issue a tpareset command, the new format string settings affect only those tables that are created after the reset. Existing table columns continue to use the existing format string in DBC.TVFields unless you submit an ALTER TABLE request to change it.
Instead, you must drop an existing BLOB or CLOB column with one ALTER TABLE request and then add the new BLOB or CLOB column using a separate ALTER TABLE request.
If you drop all BLOB and CLOB columns from a base table, that table is no longer bound to any BLOB or CLOB restrictions.