SELECT Constraint_Name, Constraint_type FROM USER_CONSTRAINTS WHERE TABLE_NAME= ‘Emp_1’ SELECT * FROM USER_CONSTRAINTS WHERE TABLE_NAME= ‘Table_Name’ USER_CONS_COLUMNS data dictionary views.The FOREIGN key constraint name can be checked form the.FOREIGN key can be ADDED, DROPPED, ENABLED or DISABLED but cannot modify the physical structure of the table.WHY? Because as per rule a composite FOREIGN key only can refer to a COMPOSITE UNIQUE key or a composite PRIMARY key column in the PARENT TABLE or VIEW. We’ll use this table in the below CREATE table statement to declare/reference the FOREIGN key.ĬONSTRAINT sampFK_01 FOREIGN KEY (SamID, SamName)Įxplanation: In the above example, we tried to create a composite FOREIGN key using table Samp_PK for reference the columns but it throws an error.
As per FOREIGN key rule, the column which consists of a FOREIGN key can only contain referential data, not new value.Ĭomposite FOREIGN KEY / Table Level (Out of Line) style:Įxplanation: The above SELECT statement creates a table Samp_PK without any CONSTRAINT. WHY? Because the value (90) does not exist in the column deptno of the dept table (see dept table data below).
Example #2Įxplanation: The above INSERT query inserts one record (see below image) and emp_dept value (70) exits in the dept table.Įxplanation: But we run the same insert query with a different value (90) and it returns an error. This kind of record is called the child record. It means the emp_dept column of the emp_1 table can contain only record(s) which exist in the deptno column of the dept table. Example #1ĬREATE TABLE emp_1 (emp_id NUMBER (2), emp_dept NUMBER (2) CONSTRAINT DeptID REFERENCES dept (deptno)) Įxplanation: In the above example, FOREIGN key CONSTRAINT applies on the emp_dept column that FOREIGN key referencing the deptno column from the dept table. In this section, we’ll see the implementation of Oracle FOREIGN Key and its behavior. Implementations of FOREIGN Key with Examples Table (col_1, col_2): Table is the table name that we use for referencing and col_1/2 are the columns from the Table for FOREIGN key reference.
When the constraint is OUT, OF LINE, FOREIGN KEY keyword must be specified.ĬREATE table Table_Name (col_1 Datatype (width), col_2 Data type (width) CONSTRAINT cons_name REFERENCES Table (column name)) ĬREATE table Table_Name (col_1 Datatype (width), col_2 Datatype (width), col_2 Datatype (width), CONSTRAINT cons_name FOREIGN KEY (col_1, col_2) REFERENCES Table (col_1, col_2) Įxplanation: Col_1/2/n: The column(s) or calculation as per your requirement. The REFERENCES clause should be used when the FOREIGN key constraint is INLINE declared. Within a single user or in the same schema, no two FOREIGN keys can have the same name.ORACLE TRIGGERS can be used on a distributed Database across nodes to make enable REFERENTIAL integrity.Both Child and Parent tables that are being used for FOREIGN KEY must belong to the same Database.Maximum 32 columns can be a part of a COMPOSITE FOREIGN key combination.The REFERENCED UNIQUE / PRIMARY KEY must be existed on the PARENT TABLE or VIEW before declaring the FOREIGN KEY to reference that column.LOB, LONG, LONG RAW, VARRAY, NESTED TABLE, OBJECT, BFILE, REF, TIMESTAMP WITH TIME ZONE.Those Tables which contain only FOREIGN keys that relate to another table (s) PRIMARY key, called PURE Details.A COMPOSITE UNIQUE or PRIMARY key of the PARENT TABLE or VIEW can only be referred by a composite FOREIGN key.ORDER and DATA type must match with the corresponding FOREIGN key and REFERENCE key column(s).The same TABLE or VIEW can contain FOREIGN KEY and REFERENCE KEY.A Table or VIEW which contains the FOREIGN Key is known as child object and if FOREIGN Key column(s) references the TABLE or VIEW is known as PARENT object.If a FOREIGN KEY is applied on multiple columns, called a composite FOREIGN KEY.A FOREIGN KEY column makes a relationship with a specified PRIMARY or UNIQUE KEY.An Oracle FOREIGN key called REFERENTIAL INTIGRITY CONSTRAINT.It can be declared on the combination of columns together.It can be declared as part of the table definition.Usually applied when the constraint is specific to that column only.It can be declared as part of the definition of an individual column or attribute.Hadoop, Data Science, Statistics & others