No two rows in the table can have the same value in the field. The system uses a unique primary or secondary index to enforce this constraint.
This constraint can only be specified on a single column. To specify UNIQUE on multiple columns, use the UNIQUE definition clause.
You cannot specify a UNIQUE constraint for a QITS column (see QITS_column_name).
The system implicitly creates a unique index on any column specified as UNIQUE.
If all of the following conditions are true, then the implicitly defined index is a unique primary index.
- No explicit primary index is specified
- No explicit primary key is specified
- This is the first unique constraint defined for the table
If none of the conditions listed previously is true, then the implicitly defined index is a unique secondary index.