How to optimize slow self join performance in Oracle SQL?

Data and Databases
1

I’m struggling with a slow self join in Oracle SQL. My goal is to compare the ‘status’ column for each ‘id’ between two dates: the current date and one month later. Here’s a simplified version of my query:

SELECT *
FROM (SELECT date, id, status AS status_current FROM my_table) current
JOIN (SELECT ADD_MONTHS(date, 1) AS date, id, status AS status_next FROM my_table) next
USING (date, id);

I need this setup to check conditions like ‘status_current in (1, 3, 5) and status_next in (90, 92, 94)’. The problem is that my table is huge, and this join is taking forever.

I’ve thought about breaking it into smaller date ranges or using window functions, but I’m not sure if that would work with my complex conditions. Any ideas on how to make this faster? I’m open to PL/SQL solutions or completely different approaches if they can achieve the same result more efficiently.

2

have u tried using analytic functions? something like this might work:

SELECT date, id, status,
LEAD(status) OVER (PARTITION BY id ORDER BY date) AS status_next
FROM my_table
WHERE status IN (1,3,5) AND
LEAD(status) OVER (PARTITION BY id ORDER BY date) IN (90,92,94);

this avoids the self-join entirely. could be way faster on big tables

3

Have you considered using partitioning on the date column? This could significantly improve your query performance, especially for large datasets. By partitioning the table based on date ranges, Oracle can quickly eliminate irrelevant data partitions.

Another approach worth exploring is the use of materialized views. You could create a materialized view that pre-computes the join results for specific date ranges, refreshing it periodically. This can drastically reduce query time for frequently accessed data.

Lastly, ensure you have appropriate indexes on the ‘id’ and ‘date’ columns. A composite index on (date, id) might be particularly beneficial for your query pattern. Remember to analyze your table statistics regularly to help the optimizer make better execution plans.

These strategies, combined with careful query tuning, should help optimize your self-join performance without compromising on your complex conditional logic.

4

hm, interesting problem! have u considered using a correlated subquery instead? might look somethin like this:

SELECT t1.date, t1.id, t1.status AS status_current,
(SELECT t2.status FROM my_table t2
WHERE t2.id = t1.id AND t2.date = ADD_MONTHS(t1.date, 1)) AS status_next
FROM my_table t1
WHERE t1.status IN (1,3,5);

This could be faster for big tables. what do u think?