Temporal Referential Constraints for ANSI Bitemporal Tables - Teradata Database

Purpose  

Temporal referential constraints define a relationship between two tables whereby every value in the constrained column or columns (the foreign key (FK)) of the child table, which must include the valid-time column as part of the FK, must exist in the corresponding referenced columns (the primary key (PK)) of the parent table. Consequently, the valid-time value of every row in the child table must exist as a valid-time value in the parent table.

These constraints are not enforced by Teradata Database so are sometimes referred to as “soft referential integrity.” Although these constraints are not enforced, the Optimizer can use them to eliminate redundant joins and improve query performance.

Note: It is the responsibility of the user to ensure that these constraints are not violated.

Temporal referential constraints can be defined for valid-time period columns in temporal tables by specifying the valid-time derived period column names with the special PERIOD keyword.

Syntax  

The syntax for adding temporal referential constraints to bitemporal tables is the same as the syntax used for valid-time tables, described in “Temporal Referential Constraints for ANSI Valid-Time Tables” on page 56.

This is ANSI SQL:2011 compliant.

Usage Notes  

The system-time derived period column cannot be included in the list of referencing or referenced columns.

The PK-FK constraint applies only to rows that are open in the system-time dimension.

Because this is a relationship between valid-time columns, the referencing table and referenced table in a PK-FK temporal referential constraint relationship can be either a valid-time table or a bitemporal table. The table types do not need to match.

Example : Temporal Referential Constraint on a Valid-Time Table

CREATE MULTISET TABLE hire_contracts(

 h_eid INTEGER NOT NULL,      

 h_name VARCHAR(5) NOT NULL,

 h_terms VARCHAR(5),

 contract_start DATE NOT NULL,

 contract_end DATE NOT NULL,

 PERIOD FOR hire_period(contract_start,contract_end) AS VALIDTIME,

 PRIMARY KEY(h_eid, hire_period WITHOUT OVERLAPS)

 ) 
 PRIMARY INDEX(h_eid);

CREATE MULTISET TABLE employee_bitemporal_ri (

 eid INTEGER NOT NULL,

 ename VARCHAR(5) NOT NULL,
 deptno INTEGER NOT NULL,

 terms VARCHAR(5),

 job_start DATE NOT NULL,

 job_end DATE NOT NULL,

 PERIOD FOR job_dur(job_start,job_end) AS VALIDTIME,
 UNIQUE(eid,job_dur WITHOUT OVERLAPS), 
 sys_start TIMESTAMP(6) WITH TIME ZONE NOT NULL 
           GENERATED ALWAYS AS ROW START,
 sys_end TIMESTAMP(6) WITH TIME ZONE NOT NULL 
           GENERATED ALWAYS AS ROW END, 
 PERIOD FOR SYSTEM_TIME(sys_start,sys_end),
 FOREIGN KEY(eid,PERIOD job_dur) REFERENCES WITH NO CHECK OPTION 
   hire_contracts(h_eid, PERIOD hire_period)
 )

 PRIMARY INDEX (eid) WITH SYSTEM VERSIONING;