Mysql order by "best match"

sql

prompt-engineering

best-practices

performance

byAnton Shumikhin·Nov 19, 2024

To sort in MySQL based on the "best match", use the MATCH() ... AGAINST() method with a FULLTEXT index. This approach calculates relevance scores for efficient ordering. Here's an example:

SELECT *, MATCH(content) AGAINST('search term') AS relevance
FROM my_table
ORDER BY relevance DESC;

The above query outputs rows from my_table where the content matches the 'search term' and ranks them based on their relevance, from highest to lowest.

But wait! What if your table doesn't support FULLTEXT indexing? Fear not, alternative approaches involving LIKE, LOCATE, and INSTR functions are coming to your rescue!

Alternative ordering strategies without FULLTEXT

Prioritizing `LIKE` and `LOCATE`

When FULLTEXT search is not available, you can employ the LIKE and LOCATE functions to prioritize results based on the proximity to the search term. A CASE statement can be used to set the order of importance:

-- If Salamander's army lined up by height: 
SELECT word
FROM words
WHERE word LIKE '%search term%'
ORDER BY CASE 
    WHEN word LIKE 'search term%' THEN 1
    WHEN word LIKE '%search term%' THEN 2
    WHEN word LIKE '%search term' THEN 3
    ELSE 4
END, LOCATE('search term', word), word;

In this query, the words where the search term starts at the beginning are given priority, followed by those that have the term anywhere in the middle, and lastly at the end. Kind of like how you might prioritize chocolate, vanilla, and strawberry ice cream. Or not. I don't judge.

Precise ordering with `INSTR`

The INSTR function can add an extra layer of precision by finding the starting position of the search term within the word. The ORDER BY clause can then use this information for sorting:

-- Like finding a raisin in a bakery, but easier.
SELECT word
FROM words
WHERE word LIKE '%search term%'
ORDER BY INSTR(word, 'search term'), word;

Words where the search term appears sooner (has a smaller 'raisin to bun ration' / INSTR value) are ranked higher.

Breaking ties alphabetically

When words have the same value for the search term, you can resort to the tie-breaker method, which uses an additional level in the ORDER BY clause to sort them in alphabetical order:

ORDER BY INSTR(word, 'search term'), word ASC;

Special conditions and potential pitfalls

Language specific rules

The linguistic rules of different languages might require you to tweak the CASE conditions or ORDER BY logic. Be sure to tailor it to your specific needs.

Wildcard usage with `LIKE`

When using the % wildcard in LIKE, beware! Overusing it can negatively affect performance. Using the functions LOCATE or INSTR for precise positioning can mitigate this issue.

Sorting direction

Including DESC or ASC in your ORDER BY clause defines the sorting direction. Should the best match be first or last? Only you can decide!

Ensuring matching `WHERE` and `ORDER BY`

Without a matching WHERE clause, your ORDER BY might lead to unexpected results. Make sure the two are in sync, like synchronized swimmers in a database pool.

Conscious selection and ordering

When using SELECT, be selective. Only choose SELECT’s that won't leave your database gasping for air. Similarly, consider how the ORDER BY clause can best serve the user and provide the best match, not just the longest list.

Comprehensive solutions using sub-queries and multiple terms

Making results more relevant

Subqueries allow for cross-referencing across multiple related columns, thereby enhancing the relevance:

SELECT *, (
    SELECT COUNT(*)
    FROM related_table
    WHERE main_table.foreign_key = related_table.id
    AND related_table.content LIKE '%search term%'
) AS related_count
FROM main_table
ORDER BY related_count DESC, relevance DESC;

Handling multiple search terms

You could think of multiple search terms as choosing your favorite ice cream flavors. Then use dynamic queries with prepared statements or several LIKE conditions to rake in the perfect sundae:

-- If any SQL statement were an ice cream sundae, this would be it!
SELECT *
FROM my_table
WHERE (content LIKE '%term1%' OR content LIKE '%term2%')
ORDER BY (content LIKE '%term1%' AND content LIKE '%term2%') DESC, relevance DESC;