Disable Constraint In Oracle

To disable constraint in the Oracle database, we have to use ALTER … DROP with constraint name. The constraint name can be a pre-defined name generated by the Oracle database or a user-defined name.

Syntax to disable the constraint in Oracle,

ALTER TABLE tablename
DISABLE CONSTRAINT constraint-name;

Since there can be only one primary key in a table, so we can also disable the primary key constraint in Oracle using the below syntax,

ALTER TABLE tablename
DISABLE PRIMARY KEY;

In the Oracle database, whenever we are creating constraint then the Oracle server internally automatically generates a unique identification number for identifying a constraint uniquely in the format of SYS_Cn, this is also called as pre-defined constraint name. Example:-

SQL> CREATE TABLE test (
       sno NUMBER(10) UNIQUE,
       name VARCHAR2(10) UNIQUE
     );
Table created.

SQL> INSERT INTO test VALUES(1, 'abc');
1 row created.

SQL> INSERT INTO test VALUES(1, 'pqr');
ORA-00001: unique constraint (SCOTT.SYS_C0014086) violated

SQL> INSERT INTO test VALUES(2, 'abc');
ORA-00001: unique constraint (SCOTT.SYS_C0014087) violated

Here SYS_C0014086 and SYS_C0014087 are the Oracle generated unique identification number of constraint applied on sno and name columns of the test table. We can get this information from user_cons_columns.

SQL> DESC user_cons_columns;
 Name              Null?    Type
 ----------------- -------- --------------
 OWNER             NOT NULL VARCHAR2(30)
 CONSTRAINT_NAME   NOT NULL VARCHAR2(30)
 TABLE_NAME        NOT NULL VARCHAR2(30)
 COLUMN_NAME                VARCHAR2(4000)
 POSITION                   NUMBER

SQL> SELECT column_name, constraint_name
     FROM user_cons_columns
     WHERE table_name = 'TEST';

COLUMN_NAME     CONSTRAINT_NAME
-----------     ---------------
SNO             SYS_C0014086
NAME            SYS_C0014087

Note that in the above query table name TEST is given in the capital letter. Oracle table name, column names are not case sensitive but records of a table are case sensitive, and here TEST is a record of user_cons_columns.

When Constraint is enabled at table level then the pre-defined constraint name will be same of those columns.

Example of disable the constraint having pre-defined name,

SQL> ALTER TABLE test
     DISABLE CONSTRAINT SYS_C0014086;
Table altered.

SQL> SELECT column_name, constraint_name
     FROM user_cons_columns
     WHERE table_name = 'TEST';

COLUMN_NAME     CONSTRAINT_NAME
-----------     ---------------
NAME            SYS_C0014087

While enabling/disabling/droping the constriants, pre-defined constraint name creates confusion for others and just by seeing pre-defined constraint name, we can’t identify which constraint is enabled on this column.

In place of pre-defined constraint name we can also assign our own name by using CONSTRAINT keyword by using following syntax. This is called user defined constraint name.

Syntax:-
CONSTRAINT user-definedName constriantType

Example:-

SQL> CREATE TABLE test1 (
       sno NUMBER(10) CONSTRAINT unique_sno UNIQUE,
       name VARCHAR2(10)
     );
Table created.

SQL> SELECT column_name, constraint_name
     FROM user_cons_columns
     WHERE table_name = 'TEST1';
COLUMN_NAME    CONSTRAINT_NAME
-------------- --------------
SNO            UNIQUE_SNO

Note:- User-defined constraint name must be unique within a user else Oracle gives an error.

Example of disable the constraint having user-defined name,

SQL> ALTER TABLE test1
     DISABLE CONSTRAINT unique_sno;
Table altered.

Now, constraint is disabled and we can insert any value into the column.

If you enjoyed this post, share it with your friends. Do you want to share more information about the topic discussed above or do you find anything incorrect? Let us know in the comments. Thank you!

Also Learn,

1 thought on “Disable Constraint In Oracle”

  1. I have read a few good stuff here, definitely price bookmarking for revisiting. I wonder how much attempt you set to create this kind of great informative website.

Leave a Comment

Your email address will not be published.