>>> select * from TB_TEST where COLUMN_1 NOT LIKE '__________';
>>yes..it is working. but how does it work?

>Find a good SQL guide and read about "LIKE" operator.

-----------------------
:)
Create this function first:

DECLARE EXTERNAL FUNCTION STRLEN
CSTRING(32767)
RETURNS INTEGER BY VALUE
ENTRY_POINT "IB_UDF_strlen" MODULE_NAME "ib_udf"

Then use it like this:
Select * from TABLE1 where strlen(COL1)<10
-----------------------