Create index for the NVARCHAR Datatype columns.

We have facing problem with NVARCHAR datatype columns during the select with WHERE condition . The Index is not getting used even though index is available. Oracle takes FULL table Scan only .
For Eg:
Table created with ITEM_NO as NVARCHAR2(100). and we have create normal index on ITEM_NO
When I capture the run time sql from the v$session and checked SQL plan it show FULL Table scan.Sql is as below
SELECT col1, col2, col3 from table x
WHERE ITEM_NO=N'123'
If ithe abvove sql is changed as below .It takes the Index
SELECT col1, col2, col3 from table x
WHERE ITEM_NO='123'
Can any one advise why this behaviour is happing
Regards
Chandrasekar

the second statement is transformed to <convert to varchar2>(item_no)='123'.
This means Oracle can't take the index as there is a function on the indexed column.
This is likely version-dependent, reason why you always, really always need to specify your four digit version
Solution: always use N'<hardcoded literal'.
Sybrand Bakker
Senior Oracle DBA

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Create index for the NVARCHAR Datatype columns.

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