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POOracle query rewrite with virtual columns in the source table
 

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    <p>I have a table, demo_fact in Oracle 11g and it has several virtual columns defined as such:</p> <pre><code>ALTER TABLE demo_fact ADD (demo_measure_from_virtual NUMBER GENERATED ALWAYS AS (CASE WHEN demo_category_column = 20 THEN demo_numericdata_column ELSE 0 END) VIRTUAL VISIBLE); </code></pre> <p>Then I have a materialized view defined as</p> <pre><code>CREATE MATERIALIZED VIEW demo_agg_mv REFRESH FORCE ON DEMAND ENABLE QUERY REWRITE AS SELECT demo_dim_one, demo_dim_two, SUM(demo_measure_from_virtual) demo_measure_from_virtual FROM demo_fact GROUP BY demo_dim_one, demo_dim_two </code></pre> <p>Now I want Query Rewrite to kick in on the following query:</p> <pre><code>SELECT demo_dim_one, SUM(demo_measure_from_virtual) FROM demo_fact GROUP BY demo_dim_one </code></pre> <p>but it doesn't. I ran EXPLAIN_REWRITE on and here is the output:</p> <pre><code>QSM-01150: query did not rewrite QSM-01102: materialized view, DEMO_AGG_MV, requires join back to table, DEMO_FACT, on column, DEMO_MEASURE_FROM_VIRTUAL QSM-01082: Joining materialized view, DEMO_AGG_MV, with table, DEMO_FACT, not possible QSM-01102: materialized view, DEMO_AGG_MV, requires join back to table, DEMO_FACT, on column, DEMO_NUMERICDATA_COLUMN </code></pre> <p>Backstory: I'm doing this with 70M rows and 50 virtual columns (all of them have the same structure, the simple case statement above, but with a different comparison column and a different result column)</p> <p>This problem seems to only manifest when the fact table has virtual columns, but changing them to non-virtual would consume too much diskspace. Why isn't Oracle rewriting the query? What can I do to fix it?</p>
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