Constraints in TeraData

Constraints

Constraints are conditions prototype rules and applying on tables or columns in other database constraints are

(a)Domain-Based – Not null x

Check                           These are attribute of Teradata

Default

b) Entity-based – primary key[pk]

- unique key[UK]

c) Reference based-foreign key [FK]

Teradata Constraints

Unique   unique values (allows one null)

Primary    unique values + Not null+ No duplicate values

Check    validates against a condition

References   Works like foreign key

Constraints   (Condition or restriction on the column's data)

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Constraints applied at two levels

a) Column Level  On a single column we take constraint

b)Table level  On multiple columns(Composite key) we take constraints.

Syntax: Column Name data type constraint <Constraint name>

Primary key/unique/check/references.

Example:

Create set table dept

(

D Code integer primary key Not null,

D name varchar(30)

D income integer constraint CHK

Check(DINcome>30000)

)

Create set table emp

(

EID integer unique not null,

Ename varchar(30)

D Code integer constraint ref

References Dept(D code)

)

Table-level constraints

Create set table dept1

(

Party ID integer

Pname varchar(30) not null,

P DOB not null, primary key(Pname, PDOB)

)

Note: In the above situation p name, PDOB is used for unique identification of the record

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Multiple column levels(composite)

Soft referential integrity

We can remove the data in the parent even the value existed in the child

Implemented with no check option

Referential integrity

Example

Create set table emp

(

EID Integer unique, not null,

Ename varchar(30),

DCode integer constraint ref

References with no check option dept(Dcode)

)

Note

P, K UK required not null at the column level because they are associated with the index concept.