How to give a unique constraint to a combination o

Question

I have a Table with 4 Columns

Each Column will be A,B,C,D

Column A is the Primary key. Column B has unique name constraint.

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?

I tried giving the composite unique key like :

ALTER TABLE TABLENAME ADD CONSTRAINT CONSTRAINT_NAME UNIQUE (COLUMN_B, COLUMN_C, COLUMN_D)

But it is checking whether any one of the constraint is present rather than checking for the combination of unique key constraint.

Answer 1

Create a unique key on those columns

ALTER TABLE YourTable
  add CONSTRAINT YourTable_unique UNIQUE (B, C, D);

Oracle/PLSQL: Unique Constraints

Answer 2

First of all you should drop an existing Constraint by using below ALTER Query.

ALTER TABLE table_name
   DROP CONSTRAINT myUniqueConstraint;

Now, you can create a UNIQUE Constraint by using the keyword UNIQUE with the combination of required Columns.

For Example:

ALTER TABLE table_name
   ADD CONSTRAINT myUniqueConstraint UNIQUE(B, C, D);

Detailed explanation of UNIQUE Constraint here.

Answer 3

ALTER TABLE table_name DROP CONSTRAINT constraint_name;

CREATE UNIQUE INDEX constraint_name ON table_name (B,C,D)