what is Constraint? How many types of constraints in SQL ?
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Answer Posted / pandia rajan
A constraint is a property assigned to a column or the set
of columns in a table that prevents certain types of
inconsistent data values from being placed in the column
(s). Constraints are used to enforce the data integrity.
This ensures the accuracy and reliability of the data in
the database
CONSTRAINT=The threat or use of force to prevent, restrict,
or dictate the action or thought of others.
there are 7 types of constraints are there and they are
grouped in to 4 types. They are
TYPES GROUP
1.DEFAULT = DOMAIN INTEGRITY
2.NOT NULL = DOMAIN INTEGRITY
3.CHECK = DOMAIN INTEGRITY
4.FOREIGN KEY = REFERENTIAL INTEGRITY
5.UNIQUE KEY = ENTITY INTEGRITY
6.PRIMARY KEY = DOMAIN INTEGRITY
7.RULE = USER DEFINED INTEGRITY
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