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informational referential constraints

 
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mailsaurabh.tripathi

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Joined: 22 May 2008
Posts: 56
Location: hyderabad

PostPosted: Mon Jul 07, 2008 1:52 pm    Post subject: informational referential constraints
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what does informational referential constraints mean!
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dick scherrer

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Joined: 23 Nov 2006
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PostPosted: Mon Jul 07, 2008 7:53 pm    Post subject:
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Hello,

Quote:
An informational referential constraint is a referential constraint that is not enforced by DB2 during normal operations.

The quote is from here:
http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=/com.ibm.db2.doc.apsg/bjnqdref1012079.htm
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ashimer

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Joined: 13 Feb 2004
Posts: 551
Location: Bangalore

PostPosted: Mon Jul 07, 2008 8:23 pm    Post subject:
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Lets say we create a table

CREATE TABLE EMP (EMPID INT CHECK (EMPID > 1000) NOT ENFORCED
ENABLE QUERY OPTIMIZATION)

here the check constraint is an informational one ..its used to increase performance ...now if u insert a row with empid = 100 the insert will be successful but if u say SELECT * FROM EMP WHERE EMPID = 90 this will return none as u have already set an access path where empid > 1000 ...

its just like telling the optimizer that empid will always be greater than 1000 so dont chk for anything less than that ...
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