Wednesday, March 12, 2014

Default Constraints


As part of very basic TSQL interview Question in interview
A default constraint is associated with a particular attribute. It is an expression that is used as
the default value when an explicit value is not specified for the attribute when you insert a row.
For example, the following code defines a default constraint for the orderts attribute in table
name order.

(representing the order’s time stamp):

ADD CONSTRAINT DFT_Orders_orderts
DEFAULT(SYSDATETIME()) FOR orderts;

The default expression invokes the SYSDATETIME function, which returns the current date and
time value. After this default expression is defined, whenever you insert a row in the Orders
table and do not explicitly specify a value in the orderts attribute, SQL Server will set the
attribute value to SYSDATETIME.
Run clean up code DROP TABLE dbo.Orders, dbo.Employees;

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