mysql - Does creating an index on two columns x and y makes queries faster when searching on column x only? -



mysql - Does creating an index on two columns x and y makes queries faster when searching on column x only? -

does creating index on 2 columns 'x' , 'y' makes queries faster when searching on column x only? illustration have table columns 'id', 'x' , 'y'. , have 2 questions:

when create 2 separate indexes 'x' , 'y', help (make things faster) query this:

select * `table` x=1 , y=2

? believe not. not sure.

when create 1 index on 2 colums 'x' , 'y' help query like:

select * `table` x=1

? is, searching on 1 of these columns.

it might speed query. there exists feature called "index merge", can merge 2 separate indexes fulfill needs of 1 query. explain show if used. if not, 1 must add together combined index. when 2 indexes can merged depends heavily on used mysql version. whereas 5.1 not , ignored (a lot?) cases, feature more mutual used in e.g. version 5.6. this depends on order of columns within key. can create (x,y) key , (y,x). rear part of combined index can used, if parts before used. select...where x=1 index (x,y) can used, whereas index (y,x) cannot.

mysql

Comments

Post a Comment

Popular posts from this blog

xslt - DocBook 5 to PDF transform failing with error: "fo:flow" is missing child elements. Required content model: marker* -

xslt - DocBook 5 to PDF transform failing with error: "fo:flow" is missing child elements. Required content model: marker* - i've inherited doc publishing process takes docbook , builds html , pdf output, using apache fop both. project had been started, never completed. lots of tweaking, i've able of doc sets build (20+), except handful, , fail severe code 1 of these 2 conditions: "fo:flow" missing kid elements. required content model: marker* "fo:block" not valid kid of "fo:root" the xml output comes out of docbook , docbook-fop checks out well-formed. the fop error in 1 book, "endecagloss", example, points end of string: <fo:flow flow-name="xsl-region-body" start-indent="4pc" end-indent="0pt"/> here’s log output in case: [java] severe: javax.xml.transform.transformerexception: file:/scratch/publishing/hudson/jobs/build-main-endeca-documentation/workspace/serverdoc/w...
Read more

mediawiki - How do I insert tables inside infoboxes on Wikia pages? -

mediawiki - How do I insert tables inside infoboxes on Wikia pages? - i want insert tables in infoboxes. example, have proteinbox i've developed using infobox template (http://health-and-medicine.wikia.com/wiki/template:proteinbox), , fasta field big fit comfortably in proteinbox. hence collapsible table within box. this tried: {{infobox | row 1 = {| class = "mw-collapsible mw-collapsed wikitable" |- | <!-- table content --> |} }} your problem is, putting nested table within template. pipe characters ( | ) in table syntax collides pipe usage in templates. the commonly used hack around create template called template:! , containing pipe character, , utilize when need set tables, parser functions or other stuff using pipe characters, within templates. table (with every | replaced {{!}} ): {{{!}} {{!}}- {{!}} a1 {{!}} b1 {{!}}- {{!}} a2 {{!}} b2 {{!}}} ...the equivalent of {| |- | a1 | b1 |- | a2 | b2 |} furthermore, hav...
Read more

Local Service User Logged into Windows -

Local Service User Logged into Windows - i created windows service tracks app server user connected through load balancer. it retrieves user logged windows on machine, cross references active directory (ad) business relationship homecoming first name, lastly name , e-mail (for notification through website created project) there 1 scheme on network users remote system, vista system, reason returning values "local service" logged machine, it's weird , security guys impossible "local service" business relationship logged windows. here how user logged windows managementscope ms = new managementscope("\\\\.\\root\\cimv2"); objectquery query = new objectquery("select * win32_computersystem"); managementobjectsearcher searcher = new managementobjectsearcher(ms, query); foreach (managementobject mo in searcher.get()) { _username = mo["username"].tostring(); } // remove domain part username string[] usernameparts = _...
Read more