How Can UNION ALL Implement a Progressive Database Search?

Database Pattern: UNION ALL for Progressive Search

When searching for data in a database, sometimes it's necessary to adjust the search criteria incrementally until a result is found. This is commonly known as a "progressive search."

Consider the following scenario: you want to search for a single row in the image table based on a name and group ID. If that doesn't produce a result, you want to search for the same name without the group ID, and if that still doesn't yield a result, you want to search for the group ID without the name.

The Progressive Search Query

The most efficient SQL query for progressive search is:

SELECT * FROM image WHERE name = 'text' AND group_id = 10
UNION ALL
SELECT * FROM image WHERE name = 'text'
UNION ALL
SELECT * FROM image WHERE group_id = 10
LIMIT 1;

Explanation

• The first SELECT statement searches for a row where both the name and group ID match the specified values.
• The second SELECT statement searches for a row where only the name matches the specified value.
• The third SELECT statement searches for a row where only the group ID matches the specified value.
• The UNION ALL operator combines the results of these three SELECT statements.
• The LIMIT 1 clause ensures that only the first row from the combined result is returned.

Optimization

To ensure optimal performance, it's crucial to create the following indexes on the image table:

CREATE INDEX image_name_grp_idx ON image (name, group_id);
CREATE INDEX image_grp_idx ON image (group_id);

Scalability

This progressive search query is scalable and can be adapted to search for multiple parameters with varying precision. Simply add additional SELECT statements for each parameter and adjust the criteria accordingly.

Conclusion

The UNION ALL query presented here is a versatile solution for progressive search. It allows you to search for data incrementally while ensuring both speed and accuracy. By following these guidelines, you can effectively implement progressive search in your database applications.

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