Restrict the data values that can be added to a table. Also see
Constraint Clause (column)
Syntax - Table Constraint:
CONSTRAINT constrnt_name {UNIQUE|PRIMARY KEY} column constrnt_state CONSTRAINT constrnt_name CHECK(condition) constrnt_state
Syntax - Table Referential Constraint:
CONSTRAINT constrnt_name FOREIGN KEY (column,…) REFERENCES [schema.]table (column,…) [ON DELETE {CASCADE|SET NULL}] constrnt_state
'column' can be either a single column name or several columns separated with commas,
Options:
constrnt_state [[NOT] DEFERRABLE] [INITIALLY {IMMEDIATE|DEFERRED}] [RELY | NORELY] [USING INDEX using_index_clause] [ENABLE|DISABLE] [VALIDATE|NOVALIDATE] [EXCEPTIONS INTO [schema.]table] using_index_clause PCTFREE int INITTRANS int MAXTRANS int TABLESPACE tablespace_name STORAGE storage_clause NOSORT LOGGING|NOLOGGING {LOCAL|GLOBAL} PARTITION BY RANGE(column_list)( partition_clause,…)} partition_clause: PARTITION partition VALUES LESS THAN (values list) ptn_storage ptn_storage: PCTFREE int PCTUSED int INITTRANS int MAXTRANS int STORAGE storage_clause TABLESPACE tablespace LOGGING|NOLOGGING condition: An expression that evaluate to TRUE, FALSE or unknown.
Some examples:
emp_name = 'SMITH' emp_name IN ('SMITH', 'JONES', 'FRASER') hiredate > '01-JAN-01' employees.dept_id = departments.dept_id_pk EMP_sal >5000 AND emp_commission IS NULL
notes:
A referential constraint with ON DELETE CASCADE will cascade deletes - so deleting
a primary key row will delete all related foreign keys.
e.g. delete a customer and all that customer's orders will disappear.
This page does not cover the syntax for Object Table constraints.
Related Oracle Commands:
disable constraint - clause
drop constraint - clause
Syntax for Oracle constraints
ORA-00001 - Unique constraint violated. (Invalid data has been rejected)
Related Views:
DBA_CONSTRAINTS ALL_CONSTRAINTS USER_CONSTRAINTS
DBA_CONS_COLUMNS ALL_CONS_COLUMNS USER_CONS_COLUMNS
CONSTRAINT_COLUMNS
CONSTRAINT_DEFS
DBA_CROSS_REFS USER_CROSS_REFS
Valid constraint_types are:
Primary key = P
Unique Key = U
Foreign Key = R
Check, not null = C
Check (view) = V