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Mysql foreign key constraint9/22/2023 ![]() Oracle issued the following error message: SQL Error: ORA-02292: integrity constraint (OT.SYS_C0010654) violated - child record foundīecause the suppliers table (child table) has a row that references to the row which is being deleted. Similarly, attempting to delete a row with group_id 1 in the supplier_groups table will fail: DELETE FROM The following is the error message: SQL Error: ORA-02291: integrity constraint (OT.SYS_C0010646) violated - parent key not found However, the following statement will fail: INSERT INTO suppliers(supplier_name, group_id)īecause the supplier_groups has no row with id 4. The following statement works because the supplier_groups table has a row with group_id 1: INSERT INTO suppliers(supplier_name, group_id) To extend the parent-child analogy, the primary key value is taken from the parent table ( supplier_groups) and is inserted into the child table ( suppliers) i.e., the child carries a FOREIGN KEY as the parent’s DNA or genetic code.īy the way, the concept of referential integrity is all about maintaining and enforcing this parent-child relationship. The suppliers table is called a child table while the supplier_groups is referred to as a parent table. In other words, attempting to insert a row into the suppliers table that does not correspond to any row in the supplier_groups table will fail, as attempting to delete a row from the supplier_groups table where there exist dependent rows in the suppliers table. This way, the constraint is enforced by Oracle. This clause defines the group_id column in the suppliers table as a foreign key that references to the group_id column of the supplier_groups table. In this statement, the following clause was newly added: FOREIGN KEY(group_id) REFERENCES supplier_groups(group_id) Second, recreate the suppliers table with a foreign key constraint: CREATE TABLE suppliers (įOREIGN KEY( group_id) REFERENCES supplier_groups( group_id) The supplier_groups table has no row with group id 4 but nothing prevents you from inserting it into the suppliers table, which is an issue.įor example, the following query fails to get all suppliers and their groups: SELECTĪs you can see, the WD supplier is missing in the result set.Ī solution to fix this problem is to use the Oracle foreign key constraint to enforce the relationship between rows from the supplier_groups and suppliers tables.įirst, drop the suppliers table: DROP TABLE suppliers However, the following statement also works: INSERT INTO suppliers(supplier_name, group_id) To insert a new third-party supplier, you have to use the group_id 2 as follows: INSERT INTO suppliers(supplier_name, group_id) The group_id in the suppliers table is used for establishing the relationship between rows in the suppliers and supplier_groups tables.īefore inserting a row into the suppliers table, you have to look up an existing group_id in the supplier_groups table and use this value for insertion.Īssuming that the supplier_groups table contains the following data: INSERT INTO supplier_groups(group_name) In other words, one supplier group has many suppliers while each supplier must belong to a supplier group. ![]() The relationship between supplier_groups and suppliers table is one-to-many. Each supplier must belong to a supplier group. The suppliers table stores the supplier information. ![]() Each supplier group may have zero, one, or many suppliers. The supplier_groups table stores supplier groups e.g., one-time supplier, third-party supplier, and inter-co supplier. Supplier_id NUMBER GENERATED BY DEFAULT AS IDENTITY,Ĭode language: SQL (Structured Query Language) ( sql ) Group_id NUMBER GENERATED BY DEFAULT AS IDENTITY, Suppose, we have two tables supplier_groups and suppliers: CREATE TABLE supplier_groups( Let’s start with an example to clearly understand its concept. Introduction to Oracle foreign key constraintĪ foreign key is all about the relationship. ![]() Summary: in this tutorial, you will learn how to use the Oracle foreign key to establish the relationship between tables.
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