Query below check nullability attribute for the column.

Query

select tabschema as schema_name, 
    tabname as table_name,
    colname as column_name, 
    case nulls 
        when 'N' then 'not nullable'
        when 'Y' then 'is nullable'
    end as nullable 
from syscat.columns 
where tabschema not like 'SYS%' 
order by tabschema, tabname,colname; 

Columns

• schema_name - name of schema
• table_name - name of table
• column_name - column name
• nullable - nullability attribute for the column:
  • is nullable - is nullable
  • not nullable - is not nullable

Rows

• One row represents one column in the database
• Scope of rows: all columns in the database
• Ordered by schema name, table name, column name

Sample results