Referencing Columns in Another Table with FOREIGN KEY TheFOREIGN KEYconstraint in SQL establishes a relationship between two tables by linking columns in one table to those in another. For example, Example: Foreign Key in SQL Here, thecustomer_idfield in theOrderstable is aFOREIGN KEYthat referen...
The name of the table where the foreign key has been created. fk_name The name of the foreign key that you wish to disable. Example Let's look at an example of how to disable a foreign key in SQL Server (Transact-SQL) using the ALTER TABLE statement. For example, if you had create...
It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is set to their default values when the parent data is deleted or updated. Example Let's look at an example of how to create a foreign key in SQL Server (Transact-SQL) using the CREATE TABLE statemen...
The foreign key establishes the relationship between the two tables and enforces referential integrity in the SQL Server. For example, the following Employee table has a foreign key column DepartmentID that links to a primary key column of the Department table.A foreign key column can be linked...
adding MySQL Foreign Key constraint as shown below. As we can see, when we add a foreign key constraint to a table, we can optionally specify the action to be taken when a referenced record is updated or deleted in the parent table. We will look at these options through an example soon...
This following example relates parent and child tables through a single-column foreign key and shows how a foreign key constraint enforces referential integrity. Create the parent and child tables using the following SQL statements: CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ) ...
TheFOREIGN KEYconstraint is used to prevent actions that would destroy links between tables. AFOREIGN KEYis a field (or collection of fields) in one table, that refers to thePRIMARY KEYin another table. The table with the foreign key is called the child table, and the table with the prima...
SQL FOREIGN KEY ConstraintA FOREIGN KEY in one table points to a PRIMARY KEY in another table.Let's illustrate the foreign key with an example. Look at the following two tables:The "Persons" table:P_IdLastNameFirstNameAddressCity 1 Hansen Ola Timoteivn 10 Sandnes 2 Svendson Tove Borgvn ...
For an example, see Add multiple foreign key constraints to a single column. A foreign key column can reference the crdb_region column in REGIONAL BY ROW tables even if the crdb_region column is not explicitly part of a UNIQUE constraint. This is possible because crdb_region is implicitly ...
SQLForeignKeys以标准结果集的形式返回结果。 如果请求与主键关联的外键,则按FKTABLE_CAT、FKTABLE_SCHEM、FKTABLE_NAME和KEY_SEQ对结果集进行排序。 如果请求与外键关联的主键,则按PKTABLE_CAT、PKTABLE_SCHEM、PKTABLE_NAME和KEY_SEQ对结果集进行排序。 下表列出了结果集中的列。