How Can I Efficiently Find a Single Row with Decrementing Search Precision in SQL?

Finding a Single Row with Decrementing Precision Using Multiple SELECT Statements

In database operations, it may be necessary to search for a single row using multiple levels of precision. This involves incrementally decreasing the search criteria until a result is found. For instance, consider searching for an image in a table:

Problem:

Find rows in a table that meet the following conditions:

• name LIKE 'text'
• group_id = 10

If there are no results for this query, then try the following query:

• name LIKE 'text'

If there are still no results for this query , then try the following query:

• group_id = 10

Solution:

Using the UNION ALL statement, all these queries can be executed at once, thereby achieving a search with decreasing precision. This statement merges different query results in the specified order, as follows:

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;

Optimization:

To improve performance, make sure to create appropriate The index is very important. For this example, it is recommended to create an index on the following columns:

• image_name_grp_idx (name, group_id)
• image_grp_idx (group_id)

by adding LIMIT 1 clause, Postgres Performance can be optimized by stopping further queries after the first row that meets the criteria is found.

Generalization:

This method can be generalized with any number of search parameters. Just add more SELECT statements inside the UNION ALL statement.

Sort:

Although the LIMIT 1 clause only returns a single row, this method may not be practical if you want to sort the results based on relevance. In this case, a more complex query is required to achieve the sorting.

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