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Observation: UNION References Same Table
You coded a UNION with the SELECT * statements referencing the same table. Since a UNION always sorts each of its tables, the same table will be sorted more than once. The following example is a UNION of results from the same table.
SELECT * FROM SYSIBM.SYSTABLES
WHERE type = 'T'
UNION
SELECT * FROM SYSIBM.SYSTABLES
WHERE type = 'V'
Consider recoding using the OR clause.
SELECT * FROM SYSIBM.SYSTABLES
WHERE type = 'T'
OR type = 'V';