SQL Override

Target update override:(done in designer in target instance and also view in session's target option)
Update Override it is an option available in TARGET instance
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Update override with non Primary Key field in the where condition:
Ex: Target table Target1 has A1,B1 as Primary key defined (local to informatica in designer)
UPDATE OVERRIDE SQL ON TARGET TABLE:

UPDATE Target1 SET C=:TU.C,D=:TU.D
WHERE A1=:TU.A1 AND B1=:TU.B1

--// already generated by informatica
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SQLOverride and Lookup SQL Override
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Coming to SQL override it is an option available in Source Qualifier and Lookup SQL Override available in Lookup transafornmation where u can include joins ,filters,Group by and order byObviously we have some differences between those 2 Overrides...
1. SQL Override is to limit the number of incoming rows entering the mapping pipelineLookup SQL Override is to limit the number of lookup rows to avoid the whole table scan by saving the lookup time & cache it uses...
2. Lookup SQL Override uses "Order By" clause by defaultSQL Override doesn't uses it & should provide in our query if we require it
3. SQL Override can provide any kind of join by writing the queryLookup SQL Override provides only Non-Equi joins
4. Lookup SQL Override gives only one record even if it finds multiple records for a single condition SQL Override doesn't do that...
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What is the difference between ODBC , DSN , NATIVE and TCP/IP Connections
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ODBC is the database drivers which is used to connect from clinet to the relational database.
DSN is the data service name which is the name of the odbc name give by the customer in order to access from the client
NATIE Drivers is the drivers which allows the client to acess the source and target after loading them from database to the workspace
TCP/IP it is the protocal used for connecting the remote computers.here the repository contacts with informatica repository server through TCP/IP