SQL - What are various constraints used in SQL?

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What are various constraints used in SQL?

NULL
NOT NULL
CHECK
DEFAULT

Total Answers and Comments: 8

Last Update: November 06, 2009

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Best Rated Answer

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Submitted by: Durga Prasad

UNIQUE

PRIMARY KEY/FOREIGN KEY

REFERENTIAL INTEGRITY

NULL

NOT NULL

CHECK

DEFAULT

Above answer was rated as good by the following members:
kishorebabu.yenumula, kperumal75

August 24, 2005 22:30:14

pallavi

RE: What are various constraints used in SQL?

There are five classes of constraints:

NOT NULL. Specifies that a column does not accept nulls.
PRIMARY KEY. Specifies the column or columns whose values uniquely identify a row in a table. Primary key columns are automatically NOT NULL.
UNIQUE. Specifies that a column has all unique values.
CHECK. Limits the domain of acceptable values for a column.

FOREIGN KEY. Aka a DRI constraint (Declarative Relational Integrity). Identifies relationships between tables. A foreign key in a table points to a candidate key (usu. a primary key) in another table. A table can have up to 253 FOREIGN KEY contraints

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September 07, 2005 02:37:14

RE: What are various constraints used in SQL?

NOT NULL is a check constraint

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September 14, 2005 08:47:42

Durga Prasad

RE: What are various constraints used in SQL?

UNIQUE

PRIMARY KEY/FOREIGN KEY

REFERENTIAL INTEGRITY

NULL

NOT NULL

CHECK

DEFAULT

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September 30, 2005 07:18:48

V. Ramalingam

RE: What are various constraints used in SQL?

Primary Constraint

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October 04, 2005 01:19:21

anil

RE: What are various constraints used in SQL?

Primary constraints foreign constrains not null constraint

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October 15, 2005 04:32:02

annathurai

RE: What are various constraints used in SQL?

constraints

there are two type of constraints

1) table level

2)column level

integrity constraints

primary key

foreign key

not null

check

default

unique

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October 31, 2006 07:06:23

Suresh

RE: What are various constraints used in SQL?

Primary Key

Foreign Key

Unique

Not Null

Check

Two types of constraints -Table level and Column level.

Except Not null all others can be defined as Both table and column level. But Not null as only column level.

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November 06, 2009 10:11:10

orasuman9

Member Since: March 2009 Contribution: 1

RE: What are various constraints used in SQL?

The Constraints are
Primary
Unique
Check
Null

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