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Editorial Team
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Asked: 2026-05-31T20:41:26+00:00

I ran across a problem with a SQL statement today that I was able

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I ran across a problem with a SQL statement today that I was able to fix by adding additional criteria, however I really want to know why my change fixed the problem.

The problem query:

SELECT *
FROM
  (SELECT ah.*,
    com.location,
    ha.customer_number,
    d.name applicance_NAME,
    house.name house_NAME,
    dr.name RULE_NAME
FROM actionhistory ah
INNER JOIN community com
ON (t.city_id = com.city_id)
INNER JOIN house_address ha
ON (t.applicance_id   = ha.applicance_id
AND ha.status_cd = 'ACTIVE')
INNER JOIN applicance d
ON (t.applicance_id = d.applicance_id)
INNER JOIN house house
ON (house.house_id = t.house_id)
LEFT JOIN the_rule tr
ON (tr.the_rule_id = t.the_rule_id)
WHERE actionhistory_id    >= 'ACT100010000' 
ORDER BY actionhistory_id
)
WHERE rownum <= 30000;

The “fix”

SELECT *
FROM
  (SELECT ah.*,
    com.location,
    ha.customer_number,
    d.name applicance_NAME,
    house.name house_NAME,
    dr.name RULE_NAME
FROM actionhistory ah
INNER JOIN community com
ON (t.city_id = com.city_id)
INNER JOIN house_address ha
ON (t.applicance_id   = ha.applicance_id
AND ha.status_cd = 'ACTIVE')
INNER JOIN applicance d
ON (t.applicance_id = d.applicance_id)
INNER JOIN house house
ON (house.house_id = t.house_id)
LEFT JOIN the_rule tr
ON (tr.the_rule_id = t.the_rule_id)
WHERE actionhistory_id    >= 'ACT100010000' and  actionhistory_id  <= 'ACT100030000'
ORDER BY actionhistory_id
)

All of the _id columns are indexed sequences.
The first query’s explain plan had a cost of 372 and the second was 14. This is running on an Oracle 11g database.

Additionally, if actionhistory_id in the where clause is anything less than ACT100000000, the original query returns instantly.

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1 Answer

  1. Editorial Team

    This is because of the index on the actionhistory_id column.

    During the first query Oracle has to return all the index blocks containing indexes for records that come after ‘ACT100010000’, then it has to match the index to the table to get all the records, and then it pulls 29999 records from the result set.

    During the second query Oracle only has to return the index blocks containing records between ‘ACT100010000’ and ‘ACT100030000’. Then it grabs from the table those records that are represented in the index blocks. A lot less work in that step of grabbing the record after having found the index than if you use the first query.

    Noticing your last line about if the id is less than ACT100000000 – sounds to me that those records may all be in the same memory block (or in a contiguous set of blocks).

    EDIT: Please also consider what is said by Justin – I was talking about actual performance, but he is pointing out that the id being a varchar greatly increases the potential values (as opposed to a number) and that the estimated plan may reflect a greater time than reality because the optimizer doesn’t know the full range until execution. To further optimize, taking his point into consideration, you could put a function based index on the id column or you could make it a combination key, with the varchar portion in one column and the numeric portion in another.

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