SQL> create table t_2 (col_1 number, col_2 varchar2(5)); Table created. This index is automatically created by the database when the constraint is enabled.

Within a primary key constraint, at least one of the columns in the primary key for each row must be NOT NULL. Hi Asif That's not necessarily true. But it's still only one index.

So my question is how Oracle is enforcing Primary Key constraint. Creating an Index Associated with a Constraint. SQL> create unique index t_2_uk on t_2(col_1); Index created. The primary key of a table is one of the candidate keys that you give some special characteristics.
This SQL Server tutorial explains how to create, add, and drop unique constraints in SQL Server with syntax and examples. To create a primary key in a table, you use the PRIMARY KEY constraint.. Oracle PRIMARY KEY constraint examples. In addition, you can add a primary key to a table after the fact by using the ALTER TABLE statement.. As you can see, the WD supplier is missing in the result set.. A solution to fix this problem is to use the Oracle foreign key constraint to enforce the relationship between rows from the supplier_groups and suppliers tables.. First, drop the suppliers table: DROP TABLE suppliers; . So when you get the ORA-0001 error, you think that it is reporting from the constraint when it is actually from the Index !

NOT VALIDATED simply indicates that at some point in time, Oracle turned on the constraint without checking all the data, but the RELY says, ignore this and go ahead and use the constraint in query rewrite and MVs as if all the data meets the constraint. Second, recreate the suppliers table with a foreign key constraint:. asifkabirdba wrote: unique index - when we have define a column as a primary key/unique constraint then an index will be created automatically for that column. For example, a PRIMARY KEY constraint will either create an index (unique or non-unique depending) or it will find an existing suitable index and use it. SQL> ALTER TABLE TAB_TEST ADD CONSTRAINT ID_PK PRIMARY KEY (ID) USING INDEX ( CREATE INDEX ID_0P ON TAB_TEST(ID ASC) ); … o an index has nothing to do with a constraint… Typically, you create a primary key for a table when you create that table. - A unique constraint defines a column, or series of columns, that must be unique in value. When you create a UNIQUE constraint, Oracle creates a unique index to enforce the uniqueness of the values. Also tried group by to find un-unique values without success.
If an index already exists with the necessary leading columns, Oracle will simply use the existing column to police the constraints, even if the index were to be non-unique. My advice: Keep the unique constraint. In this example, I show the Unique Index and the Unique Key Constraint having the same name.