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Observation: Sort Invoked for DISTINCT
You coded a DISTINCT clause which invokes a sort unless a unique index exists for the columns against which you applied the DISTINCT. If you have defined a unique index, DISTINCT is unnecessary because all values in the columns are unique. In addition, if you use GROUP BY instead of DISTINCT, DB2 can use a non-unique index to retrieve all unique values without invoking a sort.
The select list in example below specifies DISTINCT to return unique values of C1:
SELECT DISTINCT
C1
FROM
T1
You can recode that statement using GROUP BY clause, as shown below:
SELECT
C1
FROM
T1
GROUP BY
C1