null | 易学教程

Concat operation on string and null keyword

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问题 As per my understanding, when + operator is used with two string literals, concat method is invoked to produce the expected string. Example - String s = "A" + "B"; When there is null in place of one literals as below then it is generating below output. I am confused here - why it is not throwing NullPointerException ? String str = null + "B"; System.out.println(str); Output: nullB 回答1: why it is not throwing NullPointerException . Because, string concatenation applies string conversion

Validate if a column has a null value

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问题 Which SQL would be faster to validate if a particular column has a null value or not, why? 1) SELECT * FROM TABLE1 WHERE COL1 IS NULL Execute this query and then check if you are able to read any records. If yes there are null values. 2) SELECT COUNT(COL1) FROM TABLE1 WHERE COL1 IS NULL Read the count which is returned to determine if there are any null records Working with Oracle10g and SQLServer2005. 回答1: Count(columnName) will NEVER count NULL values, count skips NULLS when you specify a

Entity Framework Linq equals value or is null

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问题 I am trying with linq to get a list of items from a view where the field LocationId is either a value or is null. The field LocationId is int?. The code which i am trying is something like this: var items = _context.Items.Where( d => d.LocationId == null || d.LocationId == query.Location).ToList(); Unfortunately, as seen with SqlProfiler the generated sql does not include d.LocationId == null. What is different from the possible duplicate question is that there where only checking for a value

SPFarm.Local is return null

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问题 SPFarm.Local is return null I have googled. x64 and x86 problem - No Access issue - No Additional 1. Database server is up 2. Sites are opening 3. CA is opening The account is 'System Account' under which the code is running. Always worked before. Now suddenly it started returning null. Any ideas? Thanks in advance. 回答1: A simple server/machine restart solved the problem. Some of my friends faced similar issue and restarting solved the issue. :) 回答2: I tried by changing from x64 or x86 to Any

Slim 3 getParsedBody() always null and empty

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问题 I'm am using the Slim Framework Version 3 and have some problems. $app-> post('/', function($request, $response){ $parsedBody = $request->getParsedBody()['email']; var_dump($parsedBody); }); result is always: null Can you help me ? 回答1: It depends how you are sending data to the route. This is a POST route, so it will expect the body data to standard form format ( application/x-www-form-urlencoded ) by default. If you are sending JSON to this route, then you need to set the Content-type

Why does this simple MySQL query not return the row?

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问题 I have a row in the table users with the username test . For some reason, though, this query returns an empty result set. SELECT `id` FROM `users` WHERE `username` = "test" AND `id` != null; However, if I remove the `id` != null segment, the query returns the result id = 1 . But 1 != NULL . How is this happening? The id field is non-nullable and is auto-increment. Thanks! 回答1: The query doesn't return a row because the predicate " id != NULL " will never return TRUE. Th reason for this is

[JNI]Accessing Arrays

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分两种情况: (1)基本元素数组 (2)对象数组 (1)基本元素数组 (i)拷贝基本元素数组: JNIEXPORT jint JNICALL Java_IntArray_sumArray(JNIEnv *env, jobject obj, jintArray arr) { jint buf[10]; jint i, sum = 0; (*env)->GetIntArrayRegion(env, arr, 0, 10, buf); //arr-->buf for (i = 0; i < 10; i++) { sum += buf[i]; } return sum; } GetIntArrayRegion的第三个参数0表示arr的起始索引,第四个参数10表示要拷贝的元素个数. (ii)获取基本元素数组的指针: GetIntArrayElements/ReleaseIntArrayElements JNIEXPORT jint JNICALL Java_IntArray_sumArray(JNIEnv *env, jobject obj, jintArray arr) { jint *carr; jint i, sum = 0; carr = (*env)->GetIntArrayElements(env, arr, NULL); if (carr == NULL) { return 0

Exclude null properties in JMS Serializer

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问题 My consumed XML API has an option to retrieve only parts of the response. This causes the resulting object to have a lot of NULL properties if this feature is used. Is there a way to actually skip NULL properties? I tried to implement an exclusion strategy with shouldSkipProperty(PropertyMetadata $property, Context $context)` but i realized there is no way to access the current property value. An example would be the following class class Hotel { /** * @Type("string") */ public $id; /** *

Exclude null properties in JMS Serializer

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Insert NULL instead of empty values using MySQLi

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问题 I have a form with some optional fields. In the database those fields are set to accept NULL. The code below will throw an error if some field is empty. Could you please assist on what is the best way to avoid this? The only solution I was thinking of is to set the vars to ' ' if is empty(). $query = "INSERT INTO gifts (dateRequest, firstName, lastName, note, lastUpdated) VALUES (?, ?, ?, ?, NOW())"; if ($stmt = $dbc->prepare($query)) { $dateRequest = $_POST['dateRequest']; $firstName = $