➤ 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 rename a constraint in the Oracle database, we can use ALTER … RENAME with Constraint name. Syntax to rename the constraint,
ALTER TABLE tableName
RENAME CONSTRAINT oldConstraintName TO newConstraintName;
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.
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, 'xyz');
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.SYS_C0014205) violated
SQL> INSERT INTO test VALUES(2, 'abc');
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.SYS_C0014206) violated
Here SYS_C0014205 and SYS_C0014206 are the Oracle generated unique identification number of constraint applied on sno and name columns of 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_C0014205
NAME SYS_C0014206
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
.
The pre-defined constraint name can create confusion for others and just by seeing the pre-defined constraint name, we can’t identify which constraint is enabled on this column. We can rename the pre-defined constraint name in the Oracle database.
Syntax to rename the constraint in Oracle,ALTER TABLE tableName
RENAME CONSTRAINT oldConstraintName TO newConstraintName;
Example:-
SQL> ALTER TABLE test
RENAME CONSTRAINT SYS_C0014364 TO unique_test;
Table altered.
SQL> SELECT column_name, constraint_name
FROM user_cons_columns
WHERE table_name = 'TEST';
COLUMN_NAME CONSTRAINT_NAME
----------- ---------------
SNO UNIQUE_TEST
NAME SYS_C0014206
When Constraint is enabled at table level then the pre-defined constraint name will be same of those columns.
Assigning User-defined Name to Constraint
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 test2 (
sno NUMBER(10) CONSTRAINT unique_sno UNIQUE,
name VARCHAR2(10)
);
Table created.
SQL> ALTER TABLE test2
ADD CONSTRAINT unique_name UNIQUE(name);
Table altered.
SQL> ALTER TABLE test2
ADD address VARCHAR2(10)
CONSTRAINT unique_address UNIQUE;
Table altered.
SQL> SELECT column_name, constraint_name
FROM user_cons_columns
WHERE table_name = 'test2';
COLUMN_NAME CONSTRAINT_NAME
-------------- --------------
SNO UNIQUE_SNO
NAME UNIQUE_NAME
ADDRESS UNIQUE_ADDRESS
Now, we can drop these constraints by the same syntax, ALTER TABLE tablename DROP CONSTRAINT constraintName;
Note:- User-defined constraint name must be unique within a user else Oracle gives error:- ORA-02264: name already used by an existing constraint
SQL> CREATE TABLE test3 (
sno number(10)
CONSTRAINT unique_sno UNIQUE
);
ORA-02264: name already used by an existing constraint
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