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What is a “constraint”?
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What is a “constraint”?
2,901 Views | (9 votes, avg: 3.56)
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A constraint allows you to apply simple referential integrity checks to a table.
There are four primary types of constraints that are currently supported by SQL Server:
PRIMARY/UNIQUE - enforces uniqueness of a particular table column.
DEFAULT - specifies a default value for a column in case an insert operation does not provide one.
FOREIGN KEY - validates that every value in a column exists in a column of another table.
CHECK - checks that every value stored in a column is in some specified list
Each type of constraint performs a specific type of action.
Default is not a constraint.
NOT NULL is one more constraint which does not allow values in the specific column to be null. And also it the only constraint which is not a table level constraint.
Yes, DEFAULT is a constraint as per SQL Server.
There are five kinds of constraints in all, Primary key, Foreign key, Unique, Check and Default.
Along with above constraints also used to drop integrity checks like Primary key, Foriegn key…. when ever Administrator wants.
A constraint is nothing but a conditon that is specified on the database
A constraint is a rule that the database manager enforces
Primary key and Unique key use to uniquely identified a row of a table but
The difference between primary and Unique constraint is
Primary key does not accept NULL value
Unique key accept NULL value
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