Menu
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.
952
To define a UNIQUE constraint, you use the UNIQUE keyword followed by one or more columns. You can define a UNIQUE constraint at the column or the table level. Only at the table level, you can define a UNIQUE constraint across multiple columns.
You cannot designate the same column or combination of columns as both a primary key and a unique key or as both a primary key and a cluster key.
UNIQUE constraint ensures that all values in a specific column is different. UNIQUE key does not allow duplicate values. UNIQUE key allows NULL values but does not allow NULL values multiple times. We can create multiple UNIQUE columns on one table however only one PRIMARY KEY for table.
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);
Create a unique key on those columns
ALTER TABLE YourTable add CONSTRAINT YourTable_unique UNIQUE (B, C, D); Oracle/PLSQL: Unique Constraints
102
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
