for such cases, I'm planning to make those constraints DEFERRABLE in oracle and send a query ("SET CONSTRAINTS ALL DEFERRED") to database through UnitOfWork so Oracle would try to check integrity constraints at commit time. In this article, I am going to discuss Referential Integrity Constraints in Oracle with Examples. You would use deferrable primary keys only when you needed the functionality (eg: when refreshing a snapshot -- the snapshot must have deferrable primary/unique constraints). To rename a constraint in the Oracle database, we can use ALTER RENAME with Constraint name. ALTER TABLE EMP DROP CONSTRAINT Z. Unless you specify novalidate, in which case the constraint is created and then the session waits on a lock. Pre-request for source table in golden gate PREREQUEST for Golden Gate: 1. Here orders are given by students. The foreign key constraint name is defined as fk_orderid, where orderid is a field in orders table defined as the primary key and works as a foreign key in the employees table. If you specify CASCADE, then Oracle Database truncates all child tables that reference table with an enabled ON DELETE CASCADE referential constraint. The reference table is called the parent table, and the table with the foreign key is called the child table. SQL>. ADD CONSTRAINT FK_Student3AFK_FName_LName. The records in the child table will not be deleted. To add constraint foreign key on a table of Oracle database you must use the alter table command and add constraint keyword. Again, list includes all table constraints and you will distinguish FKs by Type column. Oracle Database Backup Service - Version N/A and later Oracle Database Cloud Service - Version N/A and later Oracle Database - Enterprise Edition - Version 11.1.0.7 and later Oracle Database Cloud Schema Service - Version N/A and later Information in this document applies to any platform. Foreign keys with cascade delete can be defined either in CREATE TABLE or ALTER TABLE. To open designer select table, right click and choose Edit from context menu.
SQL> select count (1) from jp.manager; If the expression evaluates to true, Oracle accepts the data and carry the insert or update. Alternatively, you can also delete a Foreign Key Constraint from the SQL Server Management Studio itself. fk_cust_name FOREIGN KEY (person_name) references. add constraint.
I tried to create a foreign key constraint over multiple tables / a view which joins payment with payment_types. To open designer select table, right click and choose Edit from context menu. foreign key constraints, when the primary key constraints on the parent tables have been altered. The conflict occurred in database TestDB, table dbo.Person, column ID. commit might fail. Here, is the syntax for adding foreign key constraints in the oracle database. Redefining a table with a foreign key constraint that refers to the same table, leaves the constraint in a disabled state. A foreign key is a referential constraint between two tables. In this example once the the TEST1 table is created it is renamed along with it's columns, primary key constraint and the index that supports the primary key.-- Create a test table with a primary key. Note: While dropping the primary key constraint we first need to drop Here orders are given by students. Database Schema | Oracle Schema Objects | What is database schema?Autonomous Transactions in PL/SQLSQL Transaction Statements -Transaction Manageme Back to: Oracle Tutorials for Beginners and Professionals Referential Integrity Constraints in Oracle with Examples. Deferrable constraints are usually wrong.
Pre-request for source table in golden gate PREREQUEST for Golden Gate: 1. A foreign key is one or more columns that refer to a primary key in another table.
Note: Foreign key that use more than one column then query show with comma sign. SELECT CONS.CONSTRAINT_NAME, CONS.TABLE_NAME, COLS.COLUMN_NAME, CONS.R_CONSTRAINT_NAME, CONS_R.TABLE_NAME R_TABLE_NAME, For example, this will generate the DDL for the primary key constraint: select dbms_metadata.get_ddl ('CONSTRAINT', c.constraint_name) from user_constraints c where c.constraint_type = 'P'; . In addition, you can add a primary key to a table after the fact by using the ALTER TABLE statement. Answer: You can use dictionary scripts to generate DDL for tables, indexes and constraints, but most Oracle DBAs will use the dbms_metadata package. Creating a foreign key constraint requires at least one of the SELECT, INSERT, UPDATE, DELETE, or REFERENCES privileges on the parent table as of 5.6.22. It ensures that the other table already has a primary or unique key constraint on the corresponding columns. Lets see an example using the Employee/Department table.
If we need to drop the foreign key named fk_supplier, we need to execute the following command: ALTER TABLE products. A foreign key means that values in one table must also appear in another table. Answer: You can use dictionary scripts to generate DDL for tables, indexes and constraints, but most Oracle DBAs will use the dbms_metadata package. This is usally not expexted by various tools and also by developers. The foreign table references one or more columns (the primary key, which can be one or more columns) in the primary table; that is how the link is created. (mgr_num) references jp.manager (mgr_num)); Now I want to truncate all the tables in JPs schema and.
The table which contains a FOREIGN key called the child table. Again, list includes all table constraints and you will distinguish FKs by Type column. In this module, we'll review primary and foreign keys, delving a little more into their constraints. None of the columns in the foreign key can be of LOB, LONG, LONG RAW, VARRAY, NESTED TABLE, BFILE, REF, TIMESTAMP WITH TIME ZONE, or user-defined type. The FOREIGN KEY constraint is a key used to link two tables together. In simple words you can say that, a foreign key in one table used to point primary key in another table. RE: [sql-server-l] INSERT statement conflicted with COLUMN FOREIGN KEY constraint I think that the insert is failing because there aren't any records in the parent table with matching values for the foreign key on column 'CLN_PRF_SYS_I'. So it demonstrates relationship between tables and act as cross reference among them. Also Reads drop constraint in Oracle: We can drop the constraint in oracle using alter table command. I want to check if there are foreign keys in my database without the . Oracle FOREIGN KEY is CONSTRAINT which provides REFERENTIAL integrity and which restricts the value(s) that doesnt exist in parent TABLE or VIEW. A tab with the information about table columns will open. Once you execute the above query, the primary key constraint will be deleted from the Employee1 table. A CONSTRAINT clause can constrain a single column or group of columns in a table. all_cons_columns - has list of column names for each constraint, position column in this table defines the order of the column in constraint. ; Tags create table, create, select, insert, update, delete, drop, drop table, recycle bin, purge; Area SQL General; Contributor Mike Hichwa (Oracle) Back to: Oracle Tutorials for Beginners and Professionals Referential Integrity Constraints in Oracle with Examples. Finding Foreign Key Constraints in Oracle March 20, 2007 by JP Vijaykumar Many times developers find it difficult to delete records from parent tables when child records reference those tables through foreign key (referential integrity) constraints. Instead, you must create the table without the constraint and then add it later with an ALTER TABLE statement. Now Dropping the Not Null constraints In the Oracle database, FOREIGN KEY Constraint is used to establish the relationship between tables. Missing foreign keys after full expdp/impdp. Then we created a foreign key named fk_supplier in the products table that refers to the supplier table based on the supplier_id field. select t.table_name. Oracle uses this expression to validate the data that is being inserted or updated. jp.employee table. ALTER VIEW Emp_view ADD CONSTRAINT emp_view_unq UNIQUE (first_name) DISABLE NOVALIDATE; You can specify only unique, primary key, and foreign key constraints on views. This foreign key column establishes a direct relationship with a primary key or unique key column (referenced key) usually in another table. You can use the CREATE TABLE statement to enforce several different kinds of constraints on a table: candidate keys, primary keys, foreign keys, and check conditions. As there are foreign key references to the SYSTEMS_CONFIGURATION table, I had to first remove all foreign key references to the redundant SYSTEMS_CONFIGURATION table row prior to deleting it. Check constraints 1 2 3 From Oracle FAQ. Second, specify the FOREIGN KEY clause to defines one or more column as a foreign key and parent table with columns to which the foreign key columns reference. Table in which foreign key is defined is called Foreign table/Referencing table. Choose Design. ALTER TABLE {childTable} DROP FOREIGN KEY {foreign key constraint name}; Here childTable is the name of the table which has FOREIGN KEY constraint defined, while the foreign key constraint name is the name/symbol which was used to define the FOREIGN KEY. Problem: You want to use Primary Key Constraints and Foreign Key Constraints to enforce database integrity in Oracle. A foreign key is a way to enforce referential integrity within your Oracle database. Using the multi-table insert syntax an attempt is made to insert data into both tables with care being taken to list the MAIN table first in the statement. alter table. Check that all triggers and constraints are disable at destination On Source Machine 1. You can add a foreign key constraint to an existing table using the following ALTER TABLE syntax: ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (col_name, ) REFERENCES tbl_name (col_name,) [ON DELETE reference_option] [ON UPDATE reference_option] Oracle / PLSQL: Disable a foreign keyDescription. Once you have created a foreign key in Oracle, you may encounter a situation where you are required to disable the foreign key.SyntaxExample. In this example, we've created a primary key on the supplier table called supplier_pk. It consists of only one field - the supplier_id field. A foreign key is a way to enforce referential integrity within your Oracle database. Generally, foreign key values are based on referenced primary key values only. Unfortunately this seems to be impossible in Oracle DBMS. Read the previous post of this tutorial series before this. After migrating from Oracle 10.2 to Oracle 11.2, a problem occurs when attempting to re-enable foreign keys on a table that was loaded. A foreign key is a column in a table that does NOT uniquely identify rows in that table, but is used as a link to matching columns in other tables to indicate a relationship. To drop the referenced key and the foreign key together, use the CASCADE clause. DISABLE CONSTRAINT constraint_name; Disable foreign key example ALTER TABLE ORDERS DISABLE CONSTRAINT fk_course; Output: table ORDERS altered. A foreign key is one or more columns that refer to a primary key in another table. We provide you with an Oracle sample database named OT which is based on a global fictitious company that sells computer hardware including storage, motherboard, RAM, video card, and CPU. CONSTRAINT fk_column FOREIGN KEY (column1, column2, column_n) REFERENCES parent_table (column1, column2, column_n) ON DELETE CASCADE ); Example. Table in which foreign key is defined is called Foreign table/Referencing table. Usual problems are. An Oracle FOREIGN Key is used to define an integrity constraint that restricts the values in a Database Table. To enforce data integrity in a database, Oracle provides us with constraints.
Foreign Keys is a way to ensure data integrity in your Oracle database. Unless you specify novalidate, in which case the constraint is created and then the session waits on a lock. Primary Key Constraint (Part 2 of 2) 5:35. To create a check constraint, you define a logical expression that returns true or false. Foreign key. Here are some examples of Oracle "alter table" syntax to add foreign key constraints. FOREIGN KEY (SQL FOREIGN KEY Constraint) () (Referential Integrity). I tried to create a virtual column on Payments, which calculates the value from payment_types, but virtual columns can only reference columns in the same table. FOREIGN KEY (FName, LName) REFERENCES Student3A (FName, LName); These are some important examples of adding removing foreign key in SQL.The SQL Foreign key Constraint is integral part of design the database.Hope you like this article on SQL Drop Not null or check constraints SQL> desc emp. Creation of a foreign key is prevented on another child table of the same parent table until dml is complete. Oracle uses this expression to validate the data that is being inserted or updated. To create a primary key in a table, you use the PRIMARY KEY constraint. So it demonstrates relationship between tables and act as cross reference among them. Another way to see foreign keys i with table designer. Expand your database view. Example: To create a table which contains the following field names and data types. Primary Key Constraint (Part 1 of 2) 3:53.
The table has a primary key is also called the master table and the table has a foreign key is called the child table. , search. Queries to get the details of foreign key present in the database including column details.
Parent and child tables must use the same storage engine, and they cannot be defined as temporary tables. The referential integrity, foreign key constraint, identifies a column of a table or view as the foreign key. Note: A foreign key in one TABLE points to either a primary key or a unique key in another table in Oracle. The available referential actions are RESTRICT (the default), CASCADE, SET NULL, and NO ACTION . (Doc ID 2061890.1) Last updated on OCTOBER 21, 2019. What is Oracle FOREIGN Key?Declaration Style of FOREIGN Key. It can be declared in two ways. References Clause. The REFERENCES clause should be used when the FOREIGN key constraint is INLINE declared. Implementations of FOREIGN Key with Examples. Composite FOREIGN Key in Oracle. Conclusion. Recommended Articles. In my environment we are experiencing locking on tables. To create this database for practicing, you follow the creating the Oracle Sample Database tutorial. In the designer dialog select Constraints option. A foreign key is a column or set of column which refers to the primary key or Unique key in the same table or another table. In the relational databases, a foreign key is a field or a column that is used to establish a link between two tables. Foreign key in Oracle is a way to relate multiple Tables. I was rather new to a system with hundreds of Oracle database tables. Column Level (In-Line) Style
Otherwise, Oracle will reject the data and does not insert or update at all. A foreign key constraint enforces then referential integrity. To understand the concept of the FOREIGN KEY constraint in SQL, you can think of it as a reference link between tables that are known as the primary (or parent) and foreign (or child) tables. refresh with import from the production db. Make sure all the tables to replicate have key constraint. Can I Disable/Drop Foreign Key Constraint on Referenced Partitioned Table? SQL> SQL> -- SQL> -- Add the foreign key constraint SQL> -- SQL> alter table depend add constraint fk1 foreign key (my_id) references main (my_id); Table altered. Jump to: navigation. Foreign keys are a part of a good database design. Any DML statement (an INSERT, UPDATE, or DELETE) executed on tables defined with integrity, helps to ensures that the rows in the tables maintain their integrity. September 23, 2014. The syntax for enabling a foreign key in Oracle/PLSQL is: ALTER TABLE table_name ENABLE CONSTRAINT constraint_name; Note: Foreign key that use more than one column then query show with comma sign. For example, this will generate the DDL for the primary key constraint: select dbms_metadata.get_ddl ('CONSTRAINT', c.constraint_name) from user_constraints c where c.constraint_type = 'P'; . If you omit CASCADE, then Oracle Database does not drop the primary key or unique constraint if any foreign key references it.
SQL> select count (1) from jp.manager; If the expression evaluates to true, Oracle accepts the data and carry the insert or update. Alternatively, you can also delete a Foreign Key Constraint from the SQL Server Management Studio itself. fk_cust_name FOREIGN KEY (person_name) references. add constraint.
I tried to create a foreign key constraint over multiple tables / a view which joins payment with payment_types. To open designer select table, right click and choose Edit from context menu. foreign key constraints, when the primary key constraints on the parent tables have been altered. The conflict occurred in database TestDB, table dbo.Person, column ID. commit might fail. Here, is the syntax for adding foreign key constraints in the oracle database. Redefining a table with a foreign key constraint that refers to the same table, leaves the constraint in a disabled state. A foreign key is a referential constraint between two tables. In this example once the the TEST1 table is created it is renamed along with it's columns, primary key constraint and the index that supports the primary key.-- Create a test table with a primary key. Note: While dropping the primary key constraint we first need to drop Here orders are given by students. Database Schema | Oracle Schema Objects | What is database schema?Autonomous Transactions in PL/SQLSQL Transaction Statements -Transaction Manageme Back to: Oracle Tutorials for Beginners and Professionals Referential Integrity Constraints in Oracle with Examples. Deferrable constraints are usually wrong.
Pre-request for source table in golden gate PREREQUEST for Golden Gate: 1. A foreign key is one or more columns that refer to a primary key in another table.
Note: Foreign key that use more than one column then query show with comma sign. SELECT CONS.CONSTRAINT_NAME, CONS.TABLE_NAME, COLS.COLUMN_NAME, CONS.R_CONSTRAINT_NAME, CONS_R.TABLE_NAME R_TABLE_NAME, For example, this will generate the DDL for the primary key constraint: select dbms_metadata.get_ddl ('CONSTRAINT', c.constraint_name) from user_constraints c where c.constraint_type = 'P'; . In addition, you can add a primary key to a table after the fact by using the ALTER TABLE statement. Answer: You can use dictionary scripts to generate DDL for tables, indexes and constraints, but most Oracle DBAs will use the dbms_metadata package. Creating a foreign key constraint requires at least one of the SELECT, INSERT, UPDATE, DELETE, or REFERENCES privileges on the parent table as of 5.6.22. It ensures that the other table already has a primary or unique key constraint on the corresponding columns. Lets see an example using the Employee/Department table.
If we need to drop the foreign key named fk_supplier, we need to execute the following command: ALTER TABLE products. A foreign key means that values in one table must also appear in another table. Answer: You can use dictionary scripts to generate DDL for tables, indexes and constraints, but most Oracle DBAs will use the dbms_metadata package. This is usally not expexted by various tools and also by developers. The foreign table references one or more columns (the primary key, which can be one or more columns) in the primary table; that is how the link is created. (mgr_num) references jp.manager (mgr_num)); Now I want to truncate all the tables in JPs schema and.
The table which contains a FOREIGN key called the child table. Again, list includes all table constraints and you will distinguish FKs by Type column. In this module, we'll review primary and foreign keys, delving a little more into their constraints. None of the columns in the foreign key can be of LOB, LONG, LONG RAW, VARRAY, NESTED TABLE, BFILE, REF, TIMESTAMP WITH TIME ZONE, or user-defined type. The FOREIGN KEY constraint is a key used to link two tables together. In simple words you can say that, a foreign key in one table used to point primary key in another table. RE: [sql-server-l] INSERT statement conflicted with COLUMN FOREIGN KEY constraint I think that the insert is failing because there aren't any records in the parent table with matching values for the foreign key on column 'CLN_PRF_SYS_I'. So it demonstrates relationship between tables and act as cross reference among them. Also Reads drop constraint in Oracle: We can drop the constraint in oracle using alter table command. I want to check if there are foreign keys in my database without the . Oracle FOREIGN KEY is CONSTRAINT which provides REFERENTIAL integrity and which restricts the value(s) that doesnt exist in parent TABLE or VIEW. A tab with the information about table columns will open. Once you execute the above query, the primary key constraint will be deleted from the Employee1 table. A CONSTRAINT clause can constrain a single column or group of columns in a table. all_cons_columns - has list of column names for each constraint, position column in this table defines the order of the column in constraint. ; Tags create table, create, select, insert, update, delete, drop, drop table, recycle bin, purge; Area SQL General; Contributor Mike Hichwa (Oracle) Back to: Oracle Tutorials for Beginners and Professionals Referential Integrity Constraints in Oracle with Examples. Finding Foreign Key Constraints in Oracle March 20, 2007 by JP Vijaykumar Many times developers find it difficult to delete records from parent tables when child records reference those tables through foreign key (referential integrity) constraints. Instead, you must create the table without the constraint and then add it later with an ALTER TABLE statement. Now Dropping the Not Null constraints In the Oracle database, FOREIGN KEY Constraint is used to establish the relationship between tables. Missing foreign keys after full expdp/impdp. Then we created a foreign key named fk_supplier in the products table that refers to the supplier table based on the supplier_id field. select t.table_name. Oracle uses this expression to validate the data that is being inserted or updated. jp.employee table. ALTER VIEW Emp_view ADD CONSTRAINT emp_view_unq UNIQUE (first_name) DISABLE NOVALIDATE; You can specify only unique, primary key, and foreign key constraints on views. This foreign key column establishes a direct relationship with a primary key or unique key column (referenced key) usually in another table. You can use the CREATE TABLE statement to enforce several different kinds of constraints on a table: candidate keys, primary keys, foreign keys, and check conditions. As there are foreign key references to the SYSTEMS_CONFIGURATION table, I had to first remove all foreign key references to the redundant SYSTEMS_CONFIGURATION table row prior to deleting it. Check constraints 1 2 3 From Oracle FAQ. Second, specify the FOREIGN KEY clause to defines one or more column as a foreign key and parent table with columns to which the foreign key columns reference. Table in which foreign key is defined is called Foreign table/Referencing table. Choose Design. ALTER TABLE {childTable} DROP FOREIGN KEY {foreign key constraint name}; Here childTable is the name of the table which has FOREIGN KEY constraint defined, while the foreign key constraint name is the name/symbol which was used to define the FOREIGN KEY. Problem: You want to use Primary Key Constraints and Foreign Key Constraints to enforce database integrity in Oracle. A foreign key is a way to enforce referential integrity within your Oracle database. Using the multi-table insert syntax an attempt is made to insert data into both tables with care being taken to list the MAIN table first in the statement. alter table. Check that all triggers and constraints are disable at destination On Source Machine 1. You can add a foreign key constraint to an existing table using the following ALTER TABLE syntax: ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (col_name, ) REFERENCES tbl_name (col_name,) [ON DELETE reference_option] [ON UPDATE reference_option] Oracle / PLSQL: Disable a foreign keyDescription. Once you have created a foreign key in Oracle, you may encounter a situation where you are required to disable the foreign key.SyntaxExample. In this example, we've created a primary key on the supplier table called supplier_pk. It consists of only one field - the supplier_id field. A foreign key is a way to enforce referential integrity within your Oracle database. Generally, foreign key values are based on referenced primary key values only. Unfortunately this seems to be impossible in Oracle DBMS. Read the previous post of this tutorial series before this. After migrating from Oracle 10.2 to Oracle 11.2, a problem occurs when attempting to re-enable foreign keys on a table that was loaded. A foreign key is a column in a table that does NOT uniquely identify rows in that table, but is used as a link to matching columns in other tables to indicate a relationship. To drop the referenced key and the foreign key together, use the CASCADE clause. DISABLE CONSTRAINT constraint_name; Disable foreign key example ALTER TABLE ORDERS DISABLE CONSTRAINT fk_course; Output: table ORDERS altered. A foreign key is one or more columns that refer to a primary key in another table. We provide you with an Oracle sample database named OT which is based on a global fictitious company that sells computer hardware including storage, motherboard, RAM, video card, and CPU. CONSTRAINT fk_column FOREIGN KEY (column1, column2, column_n) REFERENCES parent_table (column1, column2, column_n) ON DELETE CASCADE ); Example. Table in which foreign key is defined is called Foreign table/Referencing table. Usual problems are. An Oracle FOREIGN Key is used to define an integrity constraint that restricts the values in a Database Table. To enforce data integrity in a database, Oracle provides us with constraints.
Foreign Keys is a way to ensure data integrity in your Oracle database. Unless you specify novalidate, in which case the constraint is created and then the session waits on a lock. Primary Key Constraint (Part 2 of 2) 5:35. To create a check constraint, you define a logical expression that returns true or false. Foreign key. Here are some examples of Oracle "alter table" syntax to add foreign key constraints. FOREIGN KEY (SQL FOREIGN KEY Constraint) () (Referential Integrity). I tried to create a virtual column on Payments, which calculates the value from payment_types, but virtual columns can only reference columns in the same table. FOREIGN KEY (FName, LName) REFERENCES Student3A (FName, LName); These are some important examples of adding removing foreign key in SQL.The SQL Foreign key Constraint is integral part of design the database.Hope you like this article on SQL Drop Not null or check constraints SQL> desc emp. Creation of a foreign key is prevented on another child table of the same parent table until dml is complete. Oracle uses this expression to validate the data that is being inserted or updated. To create a primary key in a table, you use the PRIMARY KEY constraint. So it demonstrates relationship between tables and act as cross reference among them. Another way to see foreign keys i with table designer. Expand your database view. Example: To create a table which contains the following field names and data types. Primary Key Constraint (Part 1 of 2) 3:53.
The table has a primary key is also called the master table and the table has a foreign key is called the child table. , search. Queries to get the details of foreign key present in the database including column details.
Parent and child tables must use the same storage engine, and they cannot be defined as temporary tables. The referential integrity, foreign key constraint, identifies a column of a table or view as the foreign key. Note: A foreign key in one TABLE points to either a primary key or a unique key in another table in Oracle. The available referential actions are RESTRICT (the default), CASCADE, SET NULL, and NO ACTION . (Doc ID 2061890.1) Last updated on OCTOBER 21, 2019. What is Oracle FOREIGN Key?Declaration Style of FOREIGN Key. It can be declared in two ways. References Clause. The REFERENCES clause should be used when the FOREIGN key constraint is INLINE declared. Implementations of FOREIGN Key with Examples. Composite FOREIGN Key in Oracle. Conclusion. Recommended Articles. In my environment we are experiencing locking on tables. To create this database for practicing, you follow the creating the Oracle Sample Database tutorial. In the designer dialog select Constraints option. A foreign key is a column or set of column which refers to the primary key or Unique key in the same table or another table. In the relational databases, a foreign key is a field or a column that is used to establish a link between two tables. Foreign key in Oracle is a way to relate multiple Tables. I was rather new to a system with hundreds of Oracle database tables. Column Level (In-Line) Style
Otherwise, Oracle will reject the data and does not insert or update at all. A foreign key constraint enforces then referential integrity. To understand the concept of the FOREIGN KEY constraint in SQL, you can think of it as a reference link between tables that are known as the primary (or parent) and foreign (or child) tables. refresh with import from the production db. Make sure all the tables to replicate have key constraint. Can I Disable/Drop Foreign Key Constraint on Referenced Partitioned Table? SQL> SQL> -- SQL> -- Add the foreign key constraint SQL> -- SQL> alter table depend add constraint fk1 foreign key (my_id) references main (my_id); Table altered. Jump to: navigation. Foreign keys are a part of a good database design. Any DML statement (an INSERT, UPDATE, or DELETE) executed on tables defined with integrity, helps to ensures that the rows in the tables maintain their integrity. September 23, 2014. The syntax for enabling a foreign key in Oracle/PLSQL is: ALTER TABLE table_name ENABLE CONSTRAINT constraint_name; Note: Foreign key that use more than one column then query show with comma sign. For example, this will generate the DDL for the primary key constraint: select dbms_metadata.get_ddl ('CONSTRAINT', c.constraint_name) from user_constraints c where c.constraint_type = 'P'; . If you omit CASCADE, then Oracle Database does not drop the primary key or unique constraint if any foreign key references it.