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balaji.s 2 posts Joined 07/06
11 Jul 2006
Guidance relating to secondary index and unique column constraint

When we create a table and specify a unique constraint on a specific column(s), and we are not specifying any secondary indexes, but the table is created with secondary indexes with all the columns specified as unique.This is actually a disk overhead as per my view. we might have a column as unique but doesn't have that column as a access path or to be straight we need not have it as a secondary index.And also if we drop the secondary index the constraint unique is also dropped and viceversa.Why secondary index is automatically getting created when we specify a column as unique.

Fred 1096 posts Joined 08/04
11 Jul 2006

If you want the DBMS to enforce uniqueness, a Unique Index is the price you have to pay. This is clearly documented.Without an index, enforcing the constraint "on the fly" during INSERT/UPDATE would be very costly (e.g. full table scans). By the way, this behavior is not unique to Teradata.

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