如何优化搜索SQL查询？

Question

I have written a search query which searches for similar names. It works with Power Set of tags and it sorts by similarity . for example if the search text is: shakespeare tragedy hamlet

the SQL generated is:

SELECT DISTINCT id FROM (
    (SELECT * FROM books 
      WHERE name LIKE '%shakespeare%' 
      AND name LIKE '%tragedy%' 
      AND name LIKE '%hamlet%' limit 10)
    UNION
    (SELECT * FROM books 
      WHERE name LIKE '%shakespeare%' 
      AND name LIKE '%tragedy%' limit 10)
    UNION
    (SELECT * FROM books 
      WHERE name LIKE '%shakespeare%'  
      AND name LIKE '%hamlet%' limit 10)
    UNION
    (SELECT * FROM books 
      WHERE name LIKE '%tragedy%' 
      AND name LIKE '%hamlet%' limit 10)
    UNION
    (SELECT * FROM books WHERE name LIKE '%shakespeare%' limit 10)
    UNION
    (SELECT * FROM books WHERE name LIKE '%tragedy%' limit 10)
    UNION
    (SELECT * FROM books WHERE name LIKE '%hamlet%' limit 10)
) limit 10

there are two problems:

1. The Power Set creates 2^tags - 1 unions in my query, which means if some one wants to be precise and uses 6 tags, it will be 63 unions and it makes my query much slower.

2. if the first union returns 10 rows, others are useless.

Is there a way to optimize this query?

Answer 1

We can get all boosk where name is similar to past tag and add a custom ORDER BY based on similarity. If name contains tag +1 if not 0. SO if name contains all the 3 tags sum is 3 if just one sum is 1.

SELECT DISTINCT id 
FROM books 
where name LIKE '%shakespeare%'
   OR name LIKE '%tragedy%'
   OR name LIKE '%hamlet%'
ORDER BY IF(INSTR(name, 'shakespeare')>0,1,0)+
         IF(INSTR(name, 'tragedy')>0,1,0)+
         IF(INSTR(name, 'hamlet')>0,1,0) DESC
LIMIT 10

UPDATE: ORDER BY could be based on sum or just commas

Answer 2

If you switch to FULLTEXT index and use

MATCH(name) AGAINST('shakespeare tragedy hamlet')

you can get a somewhat reasonable ordering, and run a lot faster.

If you want to insist on shakespeare being in the string, but the others are optional, this works better: '+shakespeare tragedy hamlet' .

Caveat: There are both benefits and limitations of FULLTEXT .