Thank you very much!
Zhigang
-Original Message-
From: Morgan Tocker [mailto:morgan.toc...@oracle.com]
Sent: Wednesday, February 12, 2014 10:16 AM
To: Zhigang Zhang
Cc: mysql@lists.mysql.com
Subject: Re: LIKE sql optimization
Hi Zhigang,
On Feb 11, 2014, at 8:48 PM, Zhiga
Hi Zhigang,
On Feb 11, 2014, at 8:48 PM, Zhigang Zhang wrote:
> I want to know the reason, in my opinion, to scan the smaller index data has
> better performance than to scan the whole table data.
I think I understand the question - you are asking why MySQL will not index
scan, find matching
I checked a myisam table index, the index is a copy of the whole field.
Zhigang
-Original Message-
From: Reindl Harald [mailto:h.rei...@thelounge.net]
Sent: Wednesday, February 12, 2014 10:02 AM
To: mysql@lists.mysql.com
Subject: Re: LIKE sql optimization
because a index
Same reason as why composite index works only if you supply first field or
fields ..
example index on a,b,c
if you have a query :
select * from tbl
where a = 'whatever'
and b = 'something
it will use the index ..
but a query like this one :
select * from tbl
where b = 'something'
and c = 'som
MySQL can't use index when '%' condition gives even oracle and you
can try full-text search
2014-02-12 9:55 GMT+08:00 kitlenv :
> *read how a index works technically*
>
>
> On Wed, Feb 12, 2014 at 12:48 PM, Zhigang Zhang >wrote:
>
> > I want to know the reason, in my opinion, to scan the
because a index is not just a dumb copy of the whole field
and you simply can't seek in the middle of it?
http://en.wikipedia.org/wiki/B-tree
http://mattfleming.com/node/192
Am 12.02.2014 02:48, schrieb Zhigang Zhang:
> I want to know the reason, in my opinion, to scan the smaller index data has
*read how a index works technically*
On Wed, Feb 12, 2014 at 12:48 PM, Zhigang Zhang wrote:
> I want to know the reason, in my opinion, to scan the smaller index data
> has
> better performance than to scan the whole table data.
>
>
>
>
>
> zhigang
>
>
>
> _
>
> From: Mathieu Desharnais [m
I want to know the reason, in my opinion, to scan the smaller index data has
better performance than to scan the whole table data.
zhigang
_
From: Mathieu Desharnais [mailto:mdesharn...@diffusion.cc]
Sent: Wednesday, February 12, 2014 9:41 AM
To: Zhigang Zhang; mysql@lists.mys
Sql database doesn't use index in like statement if it starts with % ..
like 'abcd%' would work though...
To use an index you can store your value using reverse function and index
it .. then your like would use the index.
2014-02-11 20:23 GMT-05:00 Zhigang Zhang :
> For example:
>
>
>
> Select
Am 12.02.2014 02:23, schrieb Zhigang Zhang:
> For example:
>
> Select * from T where col like ‘%abcd’;
>
> The table T is myisam table and we created a index on col.
>
> As we known, this like sql does not use the index created on col, it confuse
> me, why?
>
> I think in mysiam engine, the i
For example:
Select * from T where col like ‘%abcd’;
The table T is myisam table and we created a index on col.
As we known, this like sql does not use the index created on col, it confuse
me, why?
I think in mysiam engine, the index data is smaller, it can use index link
list to op
Is there some way I can have a conditional in an update?
I have this update sql (paraphrased):
update LMPROC_LIMITS
set LIMIT = sign(LIMIT) * 100 * floor(0.01 + (sign(LIMIT) * LIMIT
* ratio/100)
where SYMBOL_ID = symbolId
and CLASSTYPE = LimitType
and TYPE_ in ('minClusterPosition', 'maxClust
Hi gang,
I am looking for someone that I can pay a few hours to work with me on coming
up with a few needed QUERIES for a large mysql database. The queries will span
across tables, so I great knowledge of JOINS will most likely be necessary. We
will work using SKYPE and GoToMeeting.
Please con
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