3.4. Check

Declaring a database column to store a person's age starts with the following:

CREATE TABLE temp (age NUMBER);

This command will work, but the range of the data type far surpasses the domain of a person's age. The goal is to restrict one's age to the range: 1 to 125—any value outside that range is rejected. A dimension on the datatype can impose a restriction on the column so that any value, outside a three-digit number, is invalid data.

CREATE TABLE temp (age NUMBER(3));

A dimension scales down the range of valid values. Still, values far greater than 125 can be inserted—any three-digit number is possible. An age of 999 is not acceptable. In general, a CHECK constraint is used to restrict the data to a real world domain. To restrict ...

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