zero | 易学教程

Empty string inserting a zero, not a null

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问题 My insert statement looks like this: INSERT INTO foo (bar) VALUES (''); The bar field was created like so: bar INT(11) COLLATION: (NULL) NULL: YES DEFAULT: (NULL) MySQL version: 5.1. Shouldn’t an empty string insert a NULL? I’m not sure why I’m seeing a zero (0) being stored in the table. 回答1: MySQL by default attempts to coerce invalid values for a column to the correct type. Here, the empty string '' is of type string, which is neither an integer nor NULL. I suggest taking the following

Why do floating-point numbers have signed zeros?

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Why do doubles have -0 as well as +0 ? What is the background and significance? A. R. S. -0 is (generally) treated as 0 *******. It can result when a negative floating-point number is so close to zero that it can be considered 0 (to be clear, I'm referring to arithmetic underflow , and the results of the following computations are interpreted as being exactly ±0 , not just really small numbers). e.g. System.out.println(-1 / Float.POSITIVE_INFINITY); -0.0 If we consider the same case with a positive number, we will receive our good old 0 : System.out.println(1 / Float.POSITIVE_INFINITY); 0.0 **

Is comparing to zero faster than comparing to any other number?

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问题 Is if(!test) faster than if(test==-1) I can produce assembly but there is too much assembly produced and I can never locate the particulars I'm after. I was hoping someone just knows the answer. I would guess they are the same unless most CPU architectures have some sort of "compare to zero" short cut. thanks for any help. 回答1: Typically, yes. In typical processors testing against zero, or testing sign (negative/positive) are simple condition code checks. This means that instructions can be

Mysql count return Zero if no record found

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问题 I have a two tables. cities - id_city, city_name properties - id_property, id_city, property_name I want to display cities.city_name and next to it [properties.count(id_city)] How do I make a query that still returns zero if no records are found instead of NULL , so that I get results like this: London [123] New York [0] Berlin [11] where "New York" is [0], not NULL and not 1? 回答1: Use an outer join: select cities.city_name, count(properties.id_city) from cities left join properties on cities

Equals operator for zeros (BigDecimal / Double) in Java

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问题 A few interesting observations w.r.t equals operator on 0 and 0.0 new Double(0.0).equals(0) returns false, while new Double(0.0).equals(0.0) returns true. BigDecimal.ZERO.equals(BigDecimal.valueOf(0.0)) returns false, while BigDecimal.ZERO.equals(BigDecimal.valueOf(0)) returns true. Looks like the string comparison is being done in both the cases. Could anyone throw some light on this. Thanks. 回答1: BigDecimal 'equals' compares the value and the scale. If you only want to compare values (0 ==

Extract contours from ContourPlot in Mathematica

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问题 I have a function f(x,y) of two variables, of which I need to know the location of the curves at which it crosses zero. ContourPlot does that very efficiently (that is: it uses clever multi-grid methods, not just a brute force fine-grained scan) but just gives me a plot. I would like to have a set of values {x,y} (with some specified resolution) or perhaps some interpolating function which allows me to get access to the location of these contours. Have thought of extracting this from the

How to add a trailing zero to a price with jQuery

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So I have a script which returns a price for a product. However the price may or may not include trailing zeros so sometimes I might have: 258.22 and other times I might have 258.2 In the later case I need to add the trailing zero with jQuery. How would I go about doing this? rosscj2533 You can use javascript's toFixed method ( source ), you don't need jQuery. Example: var number = 258.2; var rounded = number.toFixed(2); // rounded = 258.20 Edit: Electric Toolbox link has succumbed to linkrot and blocks the Wayback Machine so there is no working URL for the source. Javascript has a function -

Count number of bouts separated by zeros

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问题 I have a vector like this: A = [1 2 1 1 1 4 5 0 0 1 2 0 2 3 2 2 2 0 0 0 0 33] I would like to count how many GROUPS of non zero elements it contains and save them. so I want to isolate: [1 2 1 1 1 4 5] [1 2] [2 3 2 2 2] [33] and then count the groups (they should be 4) :) Can you help me please? Thanks 回答1: To count your groups, a fast vectorized method using logical indexing is: count = sum(diff([A 0]==0)==1) This assumes that A is a row vector as in your example. This works with no zeros,

Removing Trailing Zeros in Python [duplicate]

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This question already has an answer here: Formatting floats in Python without trailing zeros 15 answers I need to find a way to convert the following strings in python: 0.000 => 0 0 => 0 123.45000 => 123.45 0000 => 0 123.4506780 => 123.450678 and so forth. I tried .rstrip('0').rstrip('.'), but that doesn't work if the input is 0 or 00. Any ideas? Thanks! Updated Generalized to maintain precision and handle unseen values: import decimal import random def format_number(num): try: dec = decimal.Decimal(num) except: return 'bad' tup = dec.as_tuple() delta = len(tup.digits) + tup.exponent digits =

Padding a fixed number with leading zeros up to a fixed length [closed]

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问题 It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 7 years ago . In Crystal Report using Visual Studio 2010, I am trying a to create a formula for the following scenario: x = any number (Fixed number of 8 digits, cant be less or greater) If Length of X is less than 8, pad the