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what is the difference between adding keys & constraints
into a phisical file
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Answer Posted / kolla ravi
Primary Key - Unique Key - Key are all possible with DDS.
Either a primary or a Unique key as required can be setup
with UNIQUE keyword at file level in DDS.These keys Do not
allow any two records with same keys.
When UNIQUE is not used then FIFO or LIFO may be used. When
nothing is specified it is understood to be FIFO.
All these need Key fields to be specified.
And in addition to this whether primary/unique or just a
key, a key field dictates the order of retrieval of records
when programs read the files.
All these what we spoke above is done through DDS. That
is : all these stay right within the object.
On the other hand it is possible to setup Constraints
externally. These being Primary/Unique/Referetinal/Check.
Once these are defined they can be controlled Externally by
enabling, Disabling or removing them on the files for which
they are defined.In this context it is worth while
understanding various states of constraints and Upd/delete
rules in this context.
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