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mailsaurabh.tripathi
Joined: 22 May 2008
Posts: 22
Location: hyderabad
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| Posted: 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
Joined: 23 Nov 2006
Posts: 8732
Location: 221 B Baker St
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| Posted: 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
Joined: 13 Feb 2004
Posts: 360
Location: Bangalore
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| Posted: 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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