null | 易学教程

How to eliminate NULL fields in TSQL

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问题 I am developing a TSQL query for SQL Server 2008 R2. I am trying to develop this query to identify one record / client. Because some of these values are NULL, I am currently doing LEFT JOINS on most of the tables. But the problem with the LEFT JOINs is that now I get > 1 record for some clients. But if I change this to INNER JOINs then some clients are excluded entirely because they have NULL values for these columns. How do I limit the query result to just one record / client regardless of

MYSQL LOAD DATA INFILE

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问题 I use LOAD DATA INFILE in mysql. In my input file I have "x" character but I have to save it to database as NULL. How can I do it? 回答1: load data infile... into table ... fields terminated by... lines terminated by ... ( my_field... ) set my_field = if(my_field = 'x', null, my_field); 回答2: load data infile... into table ... fields terminated by... lines terminated by ... ( @var... ) set my_field = if(@var = 'x', null, @var); Thanks to pekka 来源： https://stackoverflow.com/questions/4723522

passing pointer to change its value but stay still

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问题 passing pointer to change its value but stay still I am working on C++ with allegro library. there is draw_tiles function. void draw_tiles(def_small_world * s_world,BITMAP * dest){ BITMAP *TileMap=NULL; loadTilemap(s_world->tilemap,TileMap); for(int y = 0;y<SIGHTY*2+1;y++) { for(int x = 0;x<SIGHTX*2+1;x++) { pasteTile(s_world->tile[y][x].kind,TileMap,dest,x,y); } } } and loadTilemap function. void loadTilemap(int i,BITMAP * tileLayer){ char c[128]; sprintf(c,TILEPATHFORMAT,i); tileLayer= load

passing pointer to change its value but stay still

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Passing nil as a parameter in place of a TComponent

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问题 I've come across some code that's throwing an exception (EIntfCasterror Cast not supported) when it passes nil to a constructor expecting a TComponent, like so: obj := SomeClass.Create(nil); The unit this is in does not contain a form and even TForm requires a TComponent be passed to it when you call its constructor. What should I pass in place of nil if anything exists or is there a way to get it to accept nil. Thank you. Also, I don't have the source code which calls the method this is in,

how to toast a message if editText is empty by clicking button?

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问题 i have 2 edit Text in my application, 1 button to add the input numbers in the edit Text and 1 text view to display the result. I would like to put a toast message if my edit text tab is empty or null when i click the button. I have searched and tried all the solutions..and nothing seems to work. help please!! here is my code for adding the two numbers. MainActivity.java package com.example.mycalc; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android

剑指offer-57-二叉树的下一个结点 -- Java实现

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题目给定一个二叉树和其中的一个结点，请找出中序遍历顺序的下一个结点并且返回。注意，树中的结点不仅包含左右子结点，同时包含指向父结点的指针。分析思路一：分三种情况： 1、当前节点有右子树，则下一节点为右子树中的最左子节点，如果右子树无左子节点则为右子节点本身。 2、如果没有右子树，如果父节点的左子节点就是该节点本身，则下一节点即父节点。 3、如果既没有右子树，又不是父节点的左子节点，如下图的J节点，则其应往上溯，直到存在一个向上遍历的过程中存在一个节点的父节点的左子节点正好是该节点自身，则这个父节点就是下一个节点。如下图J的父节点为E，它的父节点左子节点是D而不是它，继续向上，B的左子节点是D而非E，所以继续向上，A的左子节点就是B，所以J的下一节点就是A。时间复杂度：o(N) 空间复杂度：o(N) 代码： /* public class TreeLinkNode { int val; TreeLinkNode left = null; TreeLinkNode right = null; TreeLinkNode next = null; TreeLinkNode(int val) { this.val = val; } } */ public class Solution { public TreeLinkNode GetNext ( TreeLinkNode

Does calling a method on a NULL pointer which doesn't access any data ever fail?

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问题 Will the program: #include <stdio.h> struct foo { void blah() {printf("blah\n");} int i; }; void main(int, char**) { ((foo*)NULL)->blah(); } Ever crash, or do anything other than output blah , on any compiler you are aware of? Will any function crash, when called via a NULL pointer, if it doesn't access any members (including the vtable)? There have been other questions on this topic, for instance Accessing class members on a NULL pointer and Is it legal/well-defined C++ to call a non-static

Shuold I use not exists or join statement to filter out NULLs?

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问题 SELECT * FROM employees e WHERE NOT EXISTS ( SELECT name FROM eotm_dyn d WHERE d.employeeID = e.id ) And SELECT * FROM employees a LEFT JOIN eotm_dyn b on (a.joinfield=b.joinfield) WHERE b.name IS NULL Which is more efficient,some analysis? 回答1: Assuming the column values involved can not be NULL - MySQL: LEFT JOIN/IS NULL is more efficient than NOT EXISTS - read this article for details. Oracle: They are equivalent. SQL Server: NOT EXISTS is more efficient than LEFT JOIN/IS NULL - read this

WHERE field1 IN (NULL)

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问题 I want to retrieve data from the table based on a couple of columns, some with data, other with NULL. In the first code example below, the procedure is fine - all the rows are returned. In the second example no rows are returned - because NULL=NULL return FALSE. The third example is more or less what I have in mind, when the column has NULL values, then this clause has to be "ignored" and only the data in the first two columns are used to return the rows based on these two columns. SELECT *