How Can I Efficiently Combine Multiple SELECT Statements to Find a Matching Row?

Way to Try Multiple SELECTs Until a Result is Available

Searching for a specific row in a table can involve multiple criteria with varying levels of precision. A common approach is to use multiple SELECT statements with increasing precision until a match is found, such as:

SELECT * FROM image WHERE name LIKE 'text' AND group_id = 10 LIMIT 1

SELECT * FROM image WHERE name LIKE 'text' LIMIT 1

SELECT * FROM image WHERE group_id = 10 LIMIT 1

Is There a Single-Expression Solution?

While it is not possible to write a single expression that encompasses all SELECT statements, a UNION ALL operator can be used to combine multiple SELECT statements into one query:

SELECT * FROM image WHERE name = 'name105' AND group_id = 10
UNION ALL
SELECT * FROM image WHERE name = 'name105'
UNION ALL
SELECT * FROM image WHERE group_id = 10
LIMIT 1;

This query efficiently retrieves the first row that matches any of the specified conditions, considering indexes for fast execution.

Handling Multiple Search Parameters

For cases with multiple search parameters, the UNION ALL approach can be extended by adding additional SELECT statements for each combination of parameters. For instance, if searching for an image with a specific name or group ID:

SELECT * FROM image WHERE name = 'name105' AND author = 'author10'
UNION ALL
SELECT * FROM image WHERE name = 'name105'
UNION ALL
SELECT * FROM image WHERE author = 'author10'
LIMIT 1;

Relevance Considerations

While this approach effectively combines multiple search criteria, it does not consider relevance. In cases where relevance is crucial, additional sorting or filtering in the SELECT statements may be required before applying the UNION ALL.

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