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
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
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
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
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
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
*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
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
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
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
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
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
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
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