SQL查询性能LIKE和wildecards vs. IN

Question

I just wounder if there will be a big performance difference whit these 2 queries

SELECT 
  `items_id`, `sport_id`, `sport`, `title`, `url`, 
  `Select3`, `Select6`, `id`, `data`,`image` as image,
  concat('index.php?option=sports&item=',`items_id`,'&p=C108-M108') as count_url
FROM 
  qy9zh_dataitems
WHERE Select6 LIKE '%sport%'
ORDER BY `Select9` DESC LIMIT 0, 4


SELECT 
  `items_id`, `sport_id`, `sport`, `title`, `url`, 
  `Select3`, `Select6`, `id`, `data`,`image` as image,
  concat('index.php?option=sports&item=',`items_id`,'&p=C108-M108') as count_url
FROM 
  qy9zh_dataitems 
WHERE Select6 in ('sport') 
ORDER BY `Select9` DESC LIMIT 0, 4

The queries are working just fine.. both of them.. just worried about the performance :)

Edit: A strange thing when I do some testing is this:

SELECT * FROM qy9zh_dataitems WHERE Select6 in ('kvinna') LIMIT 0, 40000

29,051 total, Query took 0.2581 sec

SELECT * FROM qy9zh_dataitems WHERE Select6 LIKE ('%kvinna%') LIMIT 0, 40000

29,113 total, Query took 0.2218 sec

Answer 1

If an index is defined on a column and you are looking for the beginning of this column as in

name LIKE 'Jo%' 

the index can be used to speed up the query. However, if you are looking for any part of a word as in

name LIKE '%man%' 

The index cannot be used.

The IN clause is generally very fast, however I do not know if it can take advantage of an index.

The speed of the query depends on the availability of an appropriate index, on the size of the table, on the distribution of the values (many rows with the same values, each row with different values) and of course on the query itself. I think that your question cannot be generally answered. Make tests and compare!

Answer 2

These are not even close to being the same queries, and therefore the performance can't be compared.

The second query can use an index on Select6 to limit the rows to those that equal sport , while the first has to look at every single row to see if it contains sport anywhere in the contents of Select6 . You're trying to compare apples and oranges.

Answer 3

These are very different criteria.

WHERE Select6 LIKE '%sport%'

will look for the case where select6 contains the word sport.

WHERE Select6 in ('sport') 

will look for the case where select6 is the word sport.

An IN criteria allows you to specify a list of possible values, and should be very fast, if you've indexed the field. A like, especially a like that is looking for the word anywhere in a string can be difficult to index at all. Where select6 like 'sport%' would look for a case where select6 starts with the word sport and would be indexable.

Answer 4

As everyone else posted, basic indexes cannot be used for searches with a leading wild card. If you think those queries are going to be the most common, you want to look at the Full Text Search functions in MySQL.

Full Text Searches provide an efficient way of finding records based on individual words in text. But even then there will be limitations (for example, searching for the word "port" would not necessarily return records like "sport").

MySQL Full Text Search