How to give a unique constraint to a combination of columns in Oracle?

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.

Solution 1

Create a unique key on those columns

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

Oracle/PLSQL: Unique Constraints

Solution 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.

Solution 3

ALTER TABLE table_name DROP CONSTRAINT constraint_name;

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

Comments

[Naveen Kumar Alone]

stackoverflow.com/questions/1109614/…

[Philip Rego]

What's the naming convention? What if you have two unrelated unique values in a table? Then 'YourTable_unique' would be the same name.

[saamorim]

@PhilipRego, you're right on your comment. The naming convention is up to the team, company, user to decide. It is just an example.

[wha7ever]

I am sorry, but I don't see difference between OP's alter query and query in this answer. Am I missing something?

[saamorim]

@whatever, the question was edited afterwards, in where they included the answer that i gave.