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What is the equivalent of the null-safe equality operator <=> in SQLite?

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问题 I need to determine what is the equivalent for SQLite of the <=> operator in MySQL. Any idea? 回答1: The IS and IS NOT operators work like = and != except when one or both of the operands are NULL. In this case, if both operands are NULL, then the IS operator evaluates to 1 (true) and the IS NOT operator evaluates to 0 (false) http://www.sqlite.org/lang_expr.html#isisnot 回答2: I have just found the "IS" operator, but not sure if it has exactly the same behaviour? 来源： https://stackoverflow.com

System.Nullable<T> What is the value of null * int value?

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问题 Consider the following statements: int? v1 = null; int? v2 = 5 * v1; What is the value of v2 ? ( null or empty string?) How can I prevent the compiler to mark it as invalid operation? Do I need to follow custom exception handling? 回答1: It's null . C# Language Specification 3.0 (Section §7.2.7: Lifted operators) For the binary operators + - * / % & | ^ << >> : a lifted form of an operator exists if the operand and result types are all non-nullable value types. The lifted form is constructed by

System.Nullable<T> What is the value of null * int value?

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Remove Nulls from multiple lists in list

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问题 I have a big list ( A ) of lists of SpatialPolygonsDataFrames. Some of the lists have null values (means there is no SpatialPolygonsDataFrame). I tried : A[!sapply(unlist(A, recursive=FALSE), is.null)] But with no result and then I tried: A_nonulls=lapply(A, na.omit) What is the right way to remove the null of every list in the bigger list? EDIT: I can't do str(A)because A has 1000 lists and is huge. The first elements from the first list is like : [[1]] NULL [[2]] NULL [[3]] NULL [[4]] NULL

How to Insert NULL Value from PHP Variable to MySQL, staying away from SQL Injection?

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问题 I have a Song Uploading Form, where I will not directly input NULL value in MySQL like: mysql_query("INSERT INTO songs ( album_id ) VALUES (NULL)". I will insert NULL from PHP Variable to MySQL, and surely being safe from SQL Injection. My SQL Table is: CREATE TABLE IF NOT EXISTS `songs` ( `song_id` int(4) NOT NULL, `song_name` varchar(64) NOT NULL, `artist_id` int(4) NOT NULL, `album_id` int(4) DEFAULT NULL, `genre_id` int(4) DEFAULT NULL PRIMARY KEY (`song_id`) ) ENGINE=InnoDB DEFAULT

Sorting IComparable objects some of which are null

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问题 Most people, when writing a refence type (class) which implements IComparable<T>, use the convention that null is LESS than any actual object. But if you try to use the opposite convention, something interesting happens: using System; using System.Collections.Generic; namespace SortingNulls { internal class Child : IComparable<Child> { public int Age; public string Name; public int CompareTo(Child other) { if (other == null) return -1; // what's your problem? return this.Age.CompareTo(other

Replace returned null values in LEFT OUTER JOIN

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问题 SELECT WO_BreakerRail.ID, indRailType.RailType, indRailType.RailCode, WO_BreakerRail.CreatedPieces, WO_BreakerRail.OutsideSource, WO_BreakerRail.Charged, WO_BreakerRail.Rejected, WO_BreakerRail.RejectedToCrop, WO_BreakerRail.Date FROM indRailType LEFT OUTER JOIN WO_BreakerRail ON indRailType.RailCode = WO_BreakerRail.RailCode AND WO_BreakerRail.Date = @date When this returns, there are NULL values in the Date column where there are no matching rows from WO_BreakerRail. Is there a way to

Detect null reference in an array

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问题 I want to detect whether or not a subrange of an array contains the null reference. Somehow like this: public static <T> boolean containsNull (T[] array, int fromInclusive, int toExclusive) { for (int i = fromInclusive; i < toExclusive; ++i) { if (array[i] == null) return true; } return false; } Is there a method like this in the Java library so I don't have to manually loop over the array? Maybe I have been spoiled by C++'s excellent support for algorithmically focused code, where I can just

Replacing any NULL fields with a string

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问题 I'm new to SQL and this problem has stumped me. I am supposed to write an SQL statement that lists all the data in a table, but if a column might contain NULL values (in this case only one field is NULL), the phrase "-NONE-" must print in that column for that row. The lab hints that I must use one or more single-row functions to accomplish this. We are using Oracle SQL Developer to test scripts. I am trying to use the REPLACE function but I keep getting errors. I've tried using NVAL, REPLACE,

msql 表insert select update delete （三）

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