I have a MySQL query (running MySQL 5.0.88), which I'm trying to speed up. The underlying table has multiple indices and for the query in question, the wrong index is used (i_active - 16.000 rows, vs. i_iln - 7 rows).
I'm not very experienced with MySQL but read there is a use index hint, which can force mySQL to use a certain index. I'm trying it like this:
SELECT art.firma USE INDEX (i_iln)
...
but this produces a MySQL error.
Question:
Can anyone tell me what I'm doing wrong? (Except running 5.0.88, which I can't change.)
You missed the
FROM table
Correct SQL should be:
SELECT art.firma FROM your_table USE INDEX (i_iln) WHERE ....
select * from table use index (idx);
http://dev.mysql.com/doc/refman/5.0/en/index-hints.html
sometimes, with use index (index_name) optimizer might go for table scan, if you use hint force index, optimizer will be forced to use index, will go for table scan only if no ways left to get the rows with provided index.
SELECT art.firma FROM art FORCE INDEX (i_iln);
for more detail on hints USE INDEX and FORCE INDEX check this link
Select Coloumn1,Coloumn2,Coloumn.... FROM TABLE_NAME USE INDEX(index_name)
WHERE Coloumn="condition";
if you have correct index thn you dnt need to use index(). your query automic select correct index.If your query slow after using index thn recheck your index ,something wrong in index.
thanks in advance.enter code here
Related
I want to make a query that select fields using 'like' but I am not satisfied with the result, for example my register says, "wood table work 45" but if my query is SELECT * FROM schema1.table1 WHERE description LIKE "%table for work%"; returns nothing, I don't want the user need write exactly "table work" or "wood table" to have a result.
Create first a FULL TEXT Index on the column you wants to query this way :
ALTER TABLE `table1`
ADD FULLTEXT INDEX `IndxDescription` (`description`);
You don't need to run an indexer daemon, MySQL does the index / reindex automatically.
FYI: Full-text is supported in InnoDB / MyISAM only in MySQL
reference : http://dev.mysql.com/doc/refman/5.7/en/fulltext-restrictions.html
If you are looking for a more robust solution, consider taking a look on ElasticSearch : https://github.com/elastic/elasticsearch
You might want to look at Natural Language Fulltext search
SELECT * FROM orders WITH (INDEX(idx));
When I fired above query I got the error
mysql #1064 - You have an error in your SQL syntax
I have created index as below
create index idx on orders(date,status);
Can anybody tell me the correct syntax?
If the index is appropriate it will be used without explicitly specifying it.
Given you are using SELECT * I would not expect your index to be used (even if the INDEX hint had the correct syntax). The choice is down to the query optimiser's heuristics.
The correct syntax is:
SELECT * FROM orders USE INDEX(idx);
Ref: Index Hints
Also, please note: 99 times out of 100, specifying an Index hint should not be done. Let the optimiser do its job.
I'm using php and MySQL with a rather large MySQL database and I am trying to use idexes for the first time. I get the concept that the server will look through the index first but I'm moving trouble getting the server to use the index. So my questions are:
Does having a primary key (thus primary index?) in the table get used over the index I'm trying to use from another column? Do I have to explicitly specify the index in the select query? (I'm using several table joins, btw)
Does anyone know of a good beginners guide to using MySQL indexes? I haven't found a good one!
An important rule for mysql indexes, say you have the following index:
KEY(A,B,C)
Then in your code you have a where clause or join such as:
WHERE B = 'mydata' AND C = 'moredata'
Mysql will not be able to make use of the index for the query because the indexes work in the order given and the column A has not been included.
The fix is to either use A in the query or re-order the index (or add a second index) as so:
KEY(C,B,A)
or (if you don`t need A at all in the WHERE/JOIN):
KEY(C,B)
Also check out explain which should help you find why your indexes are not being used.
Is it possible to create a MySQL index that drops records unless one of n fields is not null?
I know Multiple-Column Indexes exists but would this be possible?
MySQL does not support filtered/conditional indexes. See this answer for more details: https://dba.stackexchange.com/questions/43/how-to-create-a-conditional-index-on-mysql
I have a table (id, title), where id is PK. For a query SELECT * FROM table WHERE title LIKE "%stackoverflow%", I tried indexing title and fulltext indexing title. I used EXPLAIN to check if index works, and both don't work.
I am told index doesn't work for LIKE "%...%". Is this the case?
noup it wont work, however if your index is 'xxx%' it will work,
another thing is your MySQL Version is older than 5.6 your engine HAVE TO BE MyIsam or Aria, but it cannot be Innodb to have a text index