Can foreign key reference more than one table?

You can't. You can NEVER declare a foreign key to reference more than one table. You *CAN* have the fields there and use them as you are doing (that is, Item_ID can be a *NUMBER* that might be in one of several different tables. And you can build queries to do what you want.

.

Keeping this in consideration, can a SQL table have more than one foreign key?

A table may have multiple foreign keys, and each foreign key can have a different parent table. Omitting the column list in the REFERENCES clause implies that the foreign key shall reference the primary key of the referenced table. Likewise, foreign keys can be defined as part of the CREATE TABLE SQL statement.

Furthermore, how many foreign keys can a table have in Oracle? A table with a foreign key reference to itself is still limited to 253 foreign key references. Greater than 253 foreign key references are not currently available for columnstore indexes, memory-optimized tables, Stretch Database, or partitioned foreign key tables.

Also Know, can two tables share a foreign key?

There actually are simple It is logically right in database management and in fact possible and must be allowed by any RDBMS to reference a foreign key to two or more tables that wants it's primary key as a foreign key in a given table.

Can foreign key have duplicate values?

Unlike primary keys, foreign keys can contain duplicate values. Also, it is OK for them contain NULL values. Indexes aren't automatically created for foreign keys; however, as a DBA, you can define them. A table is allowed to contain more than one foreign key.

Related Question Answers

What is Normalisation in SQL?

In brief, normalization is a way of organizing the data in the database. Normalization entails organizing the columns and tables of a database to ensure that their dependencies are properly enforced by database integrity constraints. It usually divides a large table into smaller ones, so it is more efficient.

Can a foreign key be null?

A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts. A table can have many foreign keys.

How many foreign keys can you have?

For one column, you can have upto 16 foreign keys. For one table, the current recommended number is 253 although you will be limited (forced) by the performance issues before you reach that number.

Can two foreign keys reference the same primary key?

It is perfectly fine to have two foreign key columns referencing the same primary key column in a different table since each foreign key value will reference a different record in the related table.

Can a table have no primary key?

Should you create a database table without a primary key? No. Every table should have some column (or set of columns) that uniquely identifies one and only one row. It's true, without a primary key (or some unique key), you don't have an insertion anomaly if you go to insert the same data multiple times.

Can a primary key be a foreign key?

Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.

Can a table have two primary keys?

A table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key. If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).

Can we create foreign key without primary key?

Yes. We can create a Foreign key without having Primary key in the parent table. Most of us are in a misconception that we can not create a Foreign key without primary key in the parent table. That unique id can be primary key or unique key.

What is a foreign key example?

A foreign key is a column (or columns) that references a column (most often the primary key) of another table. For example, say we have two tables, a CUSTOMER table that includes all customer data, and an ORDERS table that includes all customer orders.

What is primary and foreign key?

Primary key uniquely identify a record in the table. Foreign key is a field in the table that is primary key in another table. Primary Key can't accept null values. Foreign key can accept multiple null value.

Can we delete primary key from a table?

Yes, you can. But you need to delete the foreign key constraint first in the database. Without the relationship constraints, you can pretty much drop the entire table containing the primary key as there are no more dependencies.

How do I find a foreign key in a table?

When table ORDER contains a field that is the primary-key field in table CUSTOMER, that field in table ORDER is referred to as a foreign key. When a table contains a column (or concatenation of columns) that is the same as the primary key of a table, the column is called a foreign key.

What is primary key and example?

A primary key is either an existing table column or a column that is specifically generated by the database according to a defined sequence. For example, students are routinely assigned unique identification (ID) numbers, and all adults receive government-assigned and uniquely-identifiable Social Security numbers.

What is a foreign key constraint?

SQL FOREIGN KEY Constraint. A FOREIGN KEY is a key used to link two tables together. A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table. The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables.

What is composite key in SQL?

A composite key is a combination of two or more columns in a table that can be used to uniquely identify each row in the table when the columns are combined uniqueness is guaranteed, but when it taken individually it does not guarantee uniqueness.

What is foreign key in DBMS?

A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. The concept of referential integrity is derived from foreign key theory. Foreign keys and their implementation are more complex than primary keys.

How do I remove a foreign key?

To delete a foreign key constraint

1. In Object Explorer, expand the table with the constraint and then expand Keys.
2. Right-click the constraint and then click Delete.
3. In the Delete Object dialog box, click OK.

How do you write a foreign key?

Foreign Key Using an Inline Constraint ); Using this syntax, you specify your CREATE keyword, then the table name, then open brackets. For the column, you want to specify as the foreign key, and add the word REFERENCES to the end (after the data type). Then, specify the name of the other table.

What is primary key and foreign key with example?

Foreign Key It is a field in the table that is the primary key of another table. Primary Key never accept null values. A foreign key may accept multiple null values. Primary key is a clustered index and data in the DBMS table are physically organized in the sequence of the clustered index.