Unique constraint oracle

How to create unique constraint? What is unique constraint in SQL? A unique constraint is a single field or combination of fields that uniquely defines a record.

This constraint helps in maintaining data integrity. Oracle unique constraint syntax.

As long as the data set in the group of columns is unique , entry of null values is valid in this constraint. UNIQUE CONSTRAINT Syntax. Find out what fields have this constraint.

The unique index associated with the constraint always has the name of the constraint , unless specify it explicitly otherwise. You can also avoid rebuilding the index and eliminate redundant indexes by creating new primary key and unique constraints initially disabled. Then create (or use existing) nonunique indexes to enforce the constraint.

Another option would be to modify the constraint so that it can allow duplicate values in your table. The first and universal method would be to manually adjust the constraint.

Unique constraints are like alternative primary key constraints. You can have a number of unique constraints defined and the columns can have NULL values in them, unlike a column that belongs to a primary key constraint. No rows of a table may have duplicate values in a column (the unique key) or set of columns (the composite unique key) with a unique key constraint.

Column A is the Primary key. Now I want to remove the unique constraint for column B and give a unique constraint by combining the columns B, C and D. So the table will allow only one row with a particular value in columns B,C and D. How can I give this type of a constraint ? Like all data dictionary views, this a USER_ CONSTRAINTS view if you just want to check your current schema and a DBA_ CONSTRAINTS view for administration users. The construction of the constraint name indicates a system generated constraint name. For instance, if we specify NOT NULL in a table declaration. Or indeed a primary or unique key.

Redundant indexes are also eliminated. Within a primary key constraint , at least one of the columns in the primary key for each row must be NOT NULL. The primary key of a table is one of the candidate keys that you give some special characteristics. The downside is that this is an offline operation – the table is locked in Share mode.

Kishan Mashru 5views. DataPump Import (IMPDP) Reports ORA -Unique Constraint SYS.

Drop the unique constraint. Change the constraint to allow duplicate values. Modify your SQL so that a duplicate value is not created.

To create a normal index first and then create a unique constraint. Is this even the right approach?