Using Unique and Referential Integrity Constraints

Any database containing tables with interdependent data is a good candidate for the use of integrity constraints. You can profit from their use whether your data is volatile or stable. For instance, your database might contain a table of employee and department data that is constantly changing, or it could contain a table of part number data that rarely changes even though it is frequently accessed. (Note that integrity constraints cannot be assigned to LONG columns. LONG columns are described in the chapter, "Programming with LONG Columns.")

To implement unique and referential constraints, use the CREATE TABLE command and optionally the GRANT REFERENCES command in your schema file. The following table lists the commands you might use in dealing with integrity constraints.

The concepts and syntax of integrity constraints are fully discussed in the ALLBASE/SQL Reference Manual , and database administration considerations are found in the ALLBASE/SQL Database Administration Guide . This chapter contains techniques to use when coding applications that manipulate data upon which integrity constraints have been defined.

When executing the [BULK] INSERT, UPDATE [WHERE CURRENT], or DELETE [WHERE CURRENT] commands, ALLBASE/SQL considers applicable integrity constraints depending on what the overall effect of a statement would be once it completes execution. The syntax for UNIQUE or PRIMARY KEY requires unique constraint enforcement. The syntax for REFERENCES requires referential constraint enforcement on the referencing and referenced tables involved. For example, consider the following table showing what tests must be passed for a DML command to successfully complete. Refer to the ALLBASE/SQL Reference Manual for more information on enforcing constraints.