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what is Constraint? How many types of constraints in SQL ?
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Answer Posted / shreevats
Constraints are the conditions which allows to restrict the invalid or inconsistent data in the tables.
Types of Constraints
1.Not null:Not null make any column as mandatory and it will not allows the null values.
2.Unique:It will not allows duplicate values.
3.Primary Key:A PK is used to identify a record uniquely in a table.
PK=UNIQUE+NOT NULL
4.Foreign Key or Referential Integrity constraint
:It creates the relationship between any two tables.
5.Check: It is used for enforcing business validation.
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