➤ EMP DEPT Tables Queries
➤ Set Operators in Oracle
➤ CREATE command
➤ RENAME command
➤ DROP command
➤ Default Value in Column
➤ ABS() in Oracle SQL
➤ CEIL() in Oracle SQL
➤ SYSDATE in Oracle
➤ Trunc Oracle date
➤ TO_CHAR() in Oracle
➤ GROUP BY Clause
➤ Having Clause
➤ ORDER BY Clause
➤ Constraints in Oracle
➤ Rename Constraint
➤ Disable Constraint
➤ Drop Constraint
➤ NOT NULL Constraint
➤ UNIQUE Constraint
➤ PRIMARY KEY Constraint
➤ FOREIGN KEY Constraint
➤ CHECK Constraint
➤ Unlock User in SQL Plus
➤ Find SID in Oracle database
➤ Check Database Version
➤ Check Database Size
➤ Error ORA 01031
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
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.
CONSTRAINT user-definedName constriantType
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.
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