Constraints
Constraints define the conditions imposed on the behavior of a database Table. They include:
| · | Unique Constraints - a combination of values (represented by Table columns) that uniquely identify a row in the Table; there can be several unique constraints in a database Table, one of which can be separately identified as the Primary Key of the Table |
| · | Primary Key - uniquely identifies a record in a Table, consisting of one or more columns |
| · | Foreign Key - a collection of columns (UML Attributes) that together have some operational meaning; they enforce a relationship to access data in a related Table via its Primary Key |
| · | Database Index - improves the performance of lookups and sort operations on the Table at the expense of additional storage |
| · | Check Constraints - enforces domain integrity by limiting the values that are accepted by a column |
| · | Table Trigger - SQL or code automatically executed as a result of the modification of data in a Table, to maintain consistent information across the database |
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