cursor | 易学教程

API做翻页的两种思路

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转自： https://www.cnblogs.com/cgzl/p/10706881.html 在开发API的时候，有时候数据太多了，就需要分页读取。基于偏移量的分页（Offset-based）这种方式就是会提供一个每页笔数（page size）来定义返回条目的最大数，提供一个页数（page number）来表示从哪里开始读取数据。例如： 1 SELECT * FROM "CampusResumes" ORDER BY "Name" DESC LIMIT 5 OFFSET 10; 这句话的意思就是从该表中读取数据，按照Name字段降序排序，从第10笔数据后开始读取，一共读取5笔（可能不足5笔）。这就相当于page size = 5，page number = 3的分页读取。 Offset-based分页方式实现起来非常的简单，对用户来说体验也比较好。但是还有有一些劣势的：对于大规模的数据集，效率不够高。因为数据库需要进行count和skip操作。如果数据经常发生变化，那么结果不可信。在查询的时候如果插入或删除了数据，那么某条数据可能会出现两次或者翻页的时候越界了。在分布式系统中实现起来略麻烦。这种情况下，你可能需要扫描不同的数据碎片，然后才能得到想要的数据。总体来说，当允许结果出现误差的时候，Offset-based分页还是很好用的。基于游标的分页

ShowCursor(FALSE) does not work

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问题 I know this may sound to be a duplicate question but trust me it's not. I have referred this question, but was not of much help as I am trying with a console application and the answerer himself tells he does not know the reason why ShowCursor(FALSE) does not work for console applications. This thread did not help me either. Here are the things I tried: Using ShowCursor(): while(ShowCursor(false)>=0); //did not work I first suspected that it was because of this statement in the msdn : When

Set the mouse location

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问题 I need to be able to set the mouse location to the middle of the screen/window. How can I do that? 回答1: The documentation seems to indicate that CGDisplayMoveCursorToPoint or CGWarpMouseCursorPosition will do what you're after. EDIT: To match your latest comment, I would further recommend CGWarpMouseCursorPosition , about which the docs state: For example, this function is often used to move the cursor position back to the center of the screen by games that do not want the cursor pinned by

Pagination Techniques using Google App Engine

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I want to implement pagination for my website using the Cursor feature of GAE (Java). However, there is only a forward cursor ; backward cursors are not implemented as of App Engine SDK 1.4.0. So, to implement a previous page functionality, it is suggested that I store the cursor page wise in memchache. But my question is - when new record gets added into the datastore, the old cursors for respective pages would become invalid. How do I handle such situations? Is there anyone who has already implemented this functionality with cursors in Java before? Kindly elaborate the algorithm for this.

How to maintain ListView position when using the new Loader APIs?

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In Honeycomb the Loader APIs were introduced as the proper way to provide data to an application by doing the heavy lifting on a background thread. In my application I'm working to replace all my Cursor s with Loader s that return Cursor s. Since Cursor.requery() is depreciated now, it is recommended to just call restartLoader and allow the work to again be done on a background thread and then changeCursor when it returns in onLoadFinished . All of this works wonderfully except that the ListView doesn't maintain it's scroll position when I want to requery the data, using Cursor.requery() this

Multiple cursors in nested loops in MySQL

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问题 I wish to do something which appear a bit complicated in MySQL. In fact, I wish to open a cursor, do a loop, and in this loop, open a second cursor using the data from the previous fetch to be executed, and re-loop on the results. DECLARE idind INT; DECLARE idcrit INT; DECLARE idindid INT; DECLARE done INT DEFAULT 0; DECLARE done2 INT DEFAULT 0; DECLARE curIndicateur CURSOR FOR SELECT id_indicateur FROM indicateur; DECLARE curCritereIndicateur CURSOR FOR SELECT C.id_critere FROM critere C

Set cursor to be <symbol> element

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问题 I have an HTML symbol <symbol id="arrow" viewBox="0 0 8.4666659 8.4666659"> <g transform="translate(0,-288.53334)"> <path style="fill:none;stroke:#000000;stroke-width:0.48417112;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1;" d="m 0.17215798,288.70836 8.05225192,8.04935"></path> <path style="fill:none;stroke:#000000;stroke-width:0.48417112;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1

Sublime Text 2: How to Page Up/Down without moving the cursor

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I'm on OS X 10.8.4 using ST2. When I use the Home and End keys, the viewport moves and the cursor is left alone. This is standard Mac behavior, and what I'd expect. However, when I use Page Up (pageup/pgup) and Page Down (pagedown/pgdn), the cursor moves along with the viewport. This is not how other Mac apps behave, and I'd like the cursor to be left alone for these keys too. I've been able to get this half-working by adding this to my key bindings: [ { "keys": ["pageup"], "command": "scroll_lines", "args" : {"amount": 30.0} }, { "keys": ["pagedown"], "command": "scroll_lines", "args" : {

Does Oracle 12 have problems with local collection types in SQL?

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To make a long story short I propose to discuss the code you see below. When running it: Oracle 11 compiler raises "PLS-00306: wrong number or types of arguments tips in call to 'PIPE_TABLE'" "PLS-00642: Local Collection Types Not Allowed in SQL Statement" Oracle 12 compiles the following package with no such warnings, but we have a surprise in runtime when executing the anonymous block as is - everything is fine (we may pipe some rows in the pipe_table function - it doesn't affect) now let's uncomment the line with hello; or put there a call to any procedure, and run the changed anonumous

html 鼠标指针讲解

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html 鼠标指针详情可以看 https://www.w3school.com.cn/tiy/t.asp?f=csse_cursor 测试代码： <html> <body> 请把鼠标移动到单词上，可以看到鼠标指针发生变化： Auto Crosshair Default Pointer Move e-resize ne-resize nw-resize n-resize <span style=