List Primary Key and Foreign Key Relationship in Database - SQL Server - CodeProject
I need to create a Foreign Key relationship between two SQL Server CONSTRAINT [PK_ProductCategory] PRIMARY KEY CLUSTERED. Primary keys and foreign keys are two types of constraints that can be By creating this foreign key relationship, a value for SalesPersonID. In the context of relational databases, a foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table or the same table. In simpler words, the foreign key is defined in a second table, but it refers to the primary key or Such a foreign key is known in SQL as a self- referencing or recursive.
ProductVendor table form a composite primary key constraint for this table. This prevents the insertion of duplicate rows. A table can contain only one primary key constraint.
How to create a SQL Server foreign key
A primary key cannot exceed 16 columns and a total key length of bytes. The index generated by a primary key constraint cannot cause the number of indexes on the table to exceed nonclustered indexes and 1 clustered index. If clustered or nonclustered is not specified for a primary key constraint, clustered is used if there no clustered index on the table. All columns defined within a primary key constraint must be defined as not null.
One-to-One, One-to-Many Table Relationships in SQL Server
If nullability is not specified, all columns participating in a primary key constraint have their nullability set to not null. If a primary key is defined on a CLR user-defined type column, the implementation of the type must support binary ordering. Foreign Key Constraints A foreign key FK is a column or combination of columns that is used to establish and enforce a link between the data in two tables to control the data that can be stored in the foreign key table.
In a foreign key reference, a link is created between two tables when the column or columns that hold the primary key value for one table are referenced by the column or columns in another table.
This column becomes a foreign key in the second table. For example, the Sales.
SalesOrderHeader table has a foreign key link to the Sales. SalesPerson table because there is a logical relationship between sales orders and salespeople. By creating this foreign key relationship, a value for SalesPersonID cannot be inserted into the SalesOrderHeader table if it does not already exist in the SalesPerson table. A table can reference a maximum of other tables and columns as foreign keys outgoing references.
SQL Server Requires at least compatibility level.
How to create a SQL Server foreign key
The increase has the following restrictions: A table with a foreign key reference to itself is still limited to foreign key references.
Greater than foreign key references are not currently available for columnstore indexes, memory-optimized tables, Stretch Database, or partitioned foreign key tables.
Indexes on Foreign Key Constraints Unlike primary key constraints, creating a foreign key constraint does not automatically create a corresponding index. However, manually creating an index on a foreign key is often useful for the following reasons: Foreign key columns are frequently used in join criteria when the data from related tables is combined in queries by matching the column or columns in the foreign key constraint of one table with the primary or unique key column or columns in the other table.
An index enables the Database Engine to quickly find related data in the foreign key table. However, creating this index is not required. The table designer will open as well as a new window like below.
Click on the ellipse Another window will open like below. We can change the Relationship Name Foreign Key name and also need to select the appropriate tables and columns. On the right, the referencing table Product is already selected, but underneath we need to select the column ProductCategoryID.
After making the changes, click OK. At this point we are back to the first Foreign Key screen that we saw. If you scroll down on the right pane, we can see the Delete and Update rules as shown in the image below. Select the appropriate values from the dropdown list. You can see below there are two other options in the GUI as shown below: Enforce For Replication - if you are using replication and don't want the foreign keys enforced at the subscriber for the replicated data you would select No.
Enforce Foreign Key Constraint - if you do not want to the foreign key to be checked you would select No. Setting this to No defeats the purpose of having a foreign key setup.