CONSTRAINTCOLUMNS 
The system table DOMAIN.CONSTRAINTCOLUMNS contains the columns that are specified in the CONSTRAINT definitions for all the tables for which the current database user has privileges.
Structure
SCHEMANAME |
CHAR(32) |
Name of the schema |
OWNER |
CHAR(32) |
Name of the owner |
TABLENAME |
CHAR(32) |
Name of table with the CONSTRAINT definition |
CONSTRAINTNAME |
CHAR(32) |
Name of the CONSTRAINT definition |
CONSTRAINTTYPE |
CHAR(12) |
Type of CONSTRAINT definition (CHECK | FOREIGN KEY | KEY | UNIQUE_CONST) |
COLUMNNAME |
CHAR(32) |
Name of the column |
COLUMNNO |
FIXED(4) |
Number of the column within the table or constraint |
More Information
SQL Reference Manual, CONSTRAINT Definition (constraint_definition)