default-value

问题 Is there ANY difference between those two statements?: INSERT INTO distributors (did, dname) VALUES (DEFAULT, 'XYZ Widgets'); and: INSERT INTO distributors (dname) VALUES ('XYZ Widgets'); I mean is there at least one reason to use one or another pattern in some particular situation or is it completely the same? did is a serial column. 回答1: It's exactly the same thing. No need to pick one instead of the other. Usually default keyword is handy when you have computer-generated code. It makes

问题 Which value does the default constructor of the bool type return in C++? For instance, writing int i = int(); guarantees that the variable i will be initiated always with 0. I guess such an initialization routine is possible as well: bool b = bool(); But unfortunately I could not find anywhere which value such a default bool constructor is defined to return. Is the variable b always initialized with false or true . 回答1: false . Seen in the C++14 draft N4296, section 8.5 (Initializers),

问题 I know you can change the default value of an existing column like this: ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn; But according to this my query supposed to work: ALTER TABLE MyTable ALTER COLUMN CreateDate DATETIME NOT NULL CONSTRAINT DF_Constraint DEFAULT GetDate() So here I'm trying to make my column Not Null and also set the Default value. But getting Incoorect Syntax Error near CONSTRAINT. Am I missing sth? 回答1: I think issue here is with the

问题 I am having a very annoying issue with React and checkboxes. The application I am working with requires a list of checkboxes that represent settings that are persisted in the back-end. There is an option to restore the settings to their original state . At first, I created a component that has an object like a map of settings. Each setting has a key and a boolean value. Hence: { bubbles: true, gregory: false } Is to be represented as: <input type="checkbox" value="bubbles" checked="checked" /

问题 I am having a very annoying issue with React and checkboxes. The application I am working with requires a list of checkboxes that represent settings that are persisted in the back-end. There is an option to restore the settings to their original state . At first, I created a component that has an object like a map of settings. Each setting has a key and a boolean value. Hence: { bubbles: true, gregory: false } Is to be represented as: <input type="checkbox" value="bubbles" checked="checked" /

问题 I know I could do this better with std::vector , but the application I am messing with, has already a bunch of CArray parameters on a lot of related functions ... and I will not change them all at the moment! I simply want to define an empty CArray<CClass*> — array of pointers to CClass , so the problem can not be on the CClass constructor — as the default value of a function parameter. Approach 1 If I try to do it with assignment operator and default constructor : void Function(CArray<CClass

问题 I am learning matplotlib at the moment and working on changing the rcParams. The documentation on the website appears to be very sparse. When I look here, there is only a select few examples of rc parameters that can be changed, mainly fonts or line colors, such as: rcParams['lines.linewidth'] = 2 rcParams['lines.color'] = 'r' And so forth. I am looking for ways to alter the grid and default figure size for example, but they are not listed here and are only scattered here and there across the

问题 I created a scaler UDF (called sCurrentAppUser()) in SQL Server 2012 Express and I would like to use this UDF as a default value when defining a table. But every time I try, I get an error of "'sCurrentAppUser' is not a recognized built-in function name." Since I can't post more than two links yet (reputation), I'll link to my research and references in a comment. Here's my UDF: ALTER FUNCTION [dbo].[sCurrentAppUser] () RETURNS nVarChar(128) AS BEGIN DECLARE @CurrentAppUser nVarChar(128) IF

问题 What does the C++ compiler do when coming ambiguous default parameters? For example, let's say there was a function such as: void function(int a = 0, float b = 3.1); void function(int a, float b =1.1, int c = 0); Is the above considered ambiguous? If not, what does the compiler do (how is the function matched exactly) when calling something like function1(10) ? Thanks! 回答1: The following is fine void function(int a = 0, float b = 3.1); void function(int a, float b =1.1, int c = 0); And the

问题 This question already has answers here : “Least Astonishment” and the Mutable Default Argument (31 answers) Closed 2 years ago . I am noticing the following: class c: def __init__(self, data=[]): self._data=data a=c() b=c() a._data.append(1) print b._data [1] Is this the correct behavior? 回答1: Yes, it's correct behavior. However, from your question, it appears that it's not what you expected. If you want it to match your expectations, be aware of the following: Rule 1. Do not use mutable