Sql wildcard: performance overhead? -

-

I have made this question round and a persistent opinion, or many opinions based on solid data, are based on solid data. I just want to know that using a wildcard in a SQL Selection statement makes an additional overhead from calling each item individually. I have compiled the performance plans of both of them in many different test questions, and it seems That guess always reads the same. Is it possible that some upper parts are being spent elsewhere, or have they handled it equally?

Am I specifically referred to: 

  SELECT *

vs 

  items Select item 1, item 2, etc.  

  SELECT * FROM. .

and 

  select each, column, list, from ....

will perform the same because both of them have an unused scan

The difference is:

  • Additional look in sys.column
  • To resolve the contract / signature change when the table schema changes,
  • Inability to create a cover index is actually not a tuning option at all, in fact
  • If non-schemound
  • the view will need to be refreshed using the hooks or *
    • Li> / li>

Comments

Post a Comment

Popular posts from this blog

c# - How to capture HTTP packet with SharpPcap -

-
I would like to capture all incoming HTTP packets on my machine. To do this, I am using SharpPcap which is a WinPcap The cover is. SharpPcap works very well, but it captures TCP packets and what it wants to do for me is a very low level. Does anyone know how can I easily get full HTTP requests / reactions from all these TCP packets? Thanks SharpPcap is already able to capture the packet in the same way That's what the virus does (just in the code instead of the GUI). And you can either either parse them directly or you can put them in the drive in the common .pcap file format. The steps to parse the capture are: Open a connection at any time Loop a while Or start capturing using an event callback Parsing the raw packet for the type you want If you are reading .PPP dump files In addition to calling you an offline capture reader is almost the same, there is no need to select an interface, and you can set the majority There is no need to do the modes. All st...
Read more

php - Multiple Select with Explode: only returns the word "Array" -

-
By using Wordpress I have created a multiple selection box so that users can select categories to exclude. When the page is initially loaded, I see my predefined default option. However, when I select a new value and I save ... I only see the word "Array" and have not chosen anything else? & lt; Class = "amultiple" id = "& lt; php echo $ value ['id'] ;? gt;" name = "& gt; php echo $ value ['id'] ;; gt; []" Multiple = "multiple" size = "8" & gt; & Lt ;? Php global option; Foreign currency ($ value as value $) {if (get_settings ($ value ['id']) === FALSE {$$ value ['id'] = $ value ['std']; } And {$$ value ['id'] = get_settings ($ value ['id']); }} $ Ranges = & amp; Amp; Categories ('type = post & orderbiz = name & amp; hide_empty = 1'); If ($ ranges) {$ ex_cat = implode (',', $ tt_cat_exclude); Forex Currency ($ range a...
Read more

php - jQuery AJAX Post not working -

-
I do not understand why this script does not work. It has something to do within AJAX PostScript / Function. Right now, when I submit my form, it runs php code on the same page. What it should do, send the values ​​of the form for Project_Azax.fp, then there will be a refund of success on the page which is correct or false. $ (document) .ready (function () {$ ('div # didIt'). Hide (); $ ('form [name = adminForm]'). Submit (function () ($ {'.post' ('/ project_ajax.php', {action: $ ('[name = action]') Val (), pId: $ ('[name = pId]'). Val (), name ('[Name = name]'. Val (), url: $ ('[url = url]'). Val (), summary: ('[summary = summary]'). Val ()}, Function (data) {if (data.success) {$ ('div # didIt') .Sliddown ('slow');} and {warning ('unsuccessful SA!');}}, 'Jason'); return false ;});}); What is the code for project_ajax.php below ... if ($ _ POST ['action'] == ...
Read more