Foreign key relationship with composite primary keys in SQL Server - Stack Overflow
I like to have all my tables have single/noncomposite primary keys. You can see a working example in SQL Fiddle here: webob.info#!2/b05df/1 The foreign key can not refer to part of composite primary key of other table. Because where situation may arise that one child refers to multiple parent in 1-to-1 relation. table1 and table2 has the primary, foreign key relationships. In the SQL Server world (early Sybase /MS), the use of IDENTITY was based on the architecture of a Primary keys are based on this old sequential architecture. Primary keys and foreign keys are two types of constraints that can be used to enforce data integrity in SQL Server tables. These are ProductVendor table form a composite primary key constraint for this table. By creating this foreign key relationship, a value for SalesPersonID cannot be inserted into the.
I mean come on, "despite their proven advantages in many situations"? Actually, masher2, if you had given examples or references, I would have been grateful since I haven't been able to find a good argument from the surrogate crowd apart from a few reasonable though opinionated ideas on wikipedia.
I disagree violently with the suggestion that the SSN should be used as the primary key.
Columbia University has abandoned SSNs as an identifier for a number of reasons http: There is an increasing number of people who will not disclose their SSN to just any mom n' pop tech provider for privacy and security reasons, and if you use the SSN as your PK, you lock those users out.
In my own project, I tried to avoid surrogates as much as possible, but I found that some of my tables had only a few attributes that would not be unique separately or in combination, and it did not make sense to provide more attribute columns.
Extra columns would be at least as artificial as an internal number. So for this project, I ended up agreeing with you, masher2. Celko, I'd be glad for advice on how to improve. For now, I'm glad at least to have moved away from auto increment surrogates for every single table--I used to think that was the only way to do it!
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.
Primary and Foreign Key Constraints
SQL Server Requires at least compatibility level. 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. Data from two related tables can be combined even if no primary key or foreign key constraints are defined between the tables, but a foreign key relationship between two tables indicates that the two tables have been optimized to be combined in a query that uses the keys as its criteria.
How can I create foreign key with Composite Primary key
Changes to primary key constraints are checked with foreign key constraints in related tables. Referential Integrity Although the main purpose of a foreign key constraint is to control the data that can be stored in the foreign key table, it also controls changes to data in the primary key table.
For example, if the row for a salesperson is deleted from the Sales. SalesPerson table, and the salesperson's ID is used for sales orders in the Sales. SalesOrderHeader table, the relational integrity between the two tables is broken; the deleted salesperson's sales orders are orphaned in the SalesOrderHeader table without a link to the data in the SalesPerson table.
A foreign key constraint prevents this situation.
Composite Primary key and Foreign key
The constraint enforces referential integrity by guaranteeing that changes cannot be made to data in the primary key table if those changes invalidate the link to data in the foreign key table. If an attempt is made to delete the row in a primary key table or to change a primary key value, the action will fail when the deleted or changed primary key value corresponds to a value in the foreign key constraint of another table. To successfully change or delete a row in a foreign key constraint, you must first either delete the foreign key data in the foreign key table or change the foreign key data in the foreign key table, which links the foreign key to different primary key data.Oracle SQL Tutorial 20 - How to Create Composite Primary Keys
Cascading Referential Integrity By using cascading referential integrity constraints, you can define the actions that the Database Engine takes when a user tries to delete or update a key to which existing foreign keys point. The following cascading actions can be defined.