Name
Table_Constraint_Clause
Synopsis
[CONSTRAINTconstraint_name
] {{UNIQUE | PRIMARY KEY} (column
[,column
...]) | CHECK (condition
) | FOREIGN KEY (column
[,column
...]) REFERENCES [schema
.]table_name
[(column
[,column
...])] [ON DELETE {CASCADE | SET NULL}] } [Constraint_State_Clause
]
Defines constraints on a table.
Keywords
- CONSTRAINT
Specifies a name for the constraint. If omitted, Oracle assigns a name in the form SYS_Cnnn, where nnn is an integer number.
- UNIQUE
Specifies that the value in the columns identified by column must not duplicate a value for the same column(s) in any other row of the table. The value of the column(s) in the constraint must be unique for each row in the table. Note, however, that more than one column may contain the value NULL.
- PRIMARY KEY
Specifies that the column(s) identified by column will serve as the primary key for the table in which it is defined. A primary key column must not contain NULL, and no value of the primary key may appear in the same column(s) of any other row in the table.
- CHECK
Specifies a condition that must evaluate to TRUE or NULL for the constraint to be satisfied.
- FOREIGN KEY
Specifies that one or more columns in this table participate in a foreign key referential integrity relationship.
- REFERENCES
Specifies the table and column(s) that are referenced by this foreign key constraint.
- ON DELETE CASCADE
Specifies that when a row containing a primary or unique key is deleted, dependent foreign keys will be deleted automatically.
- ON DELETE SET ...
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