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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  2 unique values (allows one null)

Primary   2 unique values + Not null+ No duplicate values

Check   2 validates against a condition

References  2 Works like foreign key

Constraints  2 (Condition or restriction on the column’s data)

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Constraints applied at two levels

a) Column Level  On 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)

)

2Create 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

Screenshot_49

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Multiple column levels(composite)

PID

Pname

1

X

2

X

1

Y

2

X

3

X


Soft referential integrity

2We can remove the data in the parent even the value existed in the child

2Implemented with no check option

2Referential integrity

Screenshot_50

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 column level because they are associated with index concept.

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