null

问题 I know this works, but I don't know why or the reasoning behind why it was made to work this way: var foo = [5, 10]; var bar = foo; console.log(foo); //[5, 10] console.log(bar); //[5, 10] bar[0] = 1; console.log(foo); //[1, 10] bar = null; console.log(foo); //[1, 10] I would have expected not just bar to become null, but foo as well. I'd love some help understanding this. 回答1: The difference is between rebinding and mutating operations. bar[0] = 1 is mutating; it affects the object that bar

问题 I have a string value read in from a CSV file. The CSV file contains 7 NULL bytes, I have confirmed this by opening it in a hex editor and sure enought there are 7 0x0 bytes in there. This string is causing me pain. In vb.net when I check the strlen of this string it returns a value of 7 and if i do a String.IsNullOrWhitespace it returns false . I cannot understand why this is? I have split the string into a byte array and each byte is 0x0 , which is null/nothing. A string = Nothing

问题 I have a TDBLookupComboBox showing a TStringField of kind fkLookup , which allows Null values (from a nullable Integer database column). The dropdown list displays the items from the assigned LookupDataSet , which comes from a joined table. If the field is Null , none of the list items are displayed, the combobox is empty. If the field has a value, the correct description is shown. I can reset it to Null by pressing the assigned NullValueKey . That's all ok, but the users prefer using the

问题 I saw that I can access the templated parts of a ComboBox (the TextBox , PopUp and Button ) via the FindName method. The TextBox should be accessible by using cb.FindName("PART_EditableTextBox") , however, this always returns null for me. As per melya's suggestion, I have tried using cb.Template.FindName("PART_EditableTextBox", cb); instead -- this works on a simple test app, but not my own. The difference, perhaps, is that I'm trying to do this before the ComboBox is loaded or initialised (I

问题 I'm trying to convert some data into sql statements with the use of Streamreader and Streamwriter. My problem is, when i split lines which in which between 2 delimiters is nothing, not even a space, they get ignored and i get a IndexOutOfRange error because my temparray only goes till temparray[3] , but it should go to like temparray[6] .. How can i split and use Null values or replace those null values with a simple char, so that i dont get an IndexOutOfRange error when i want to create my

问题 I'm trying to drill down to each value in an iteration of an array nested hash and replace all nil values with something like 'None' or 0. Please see my code that is clearly not working. I need to fix this before I pass it to my Views in Rails for iteration and rendering: My controller: def show results = Record.get_record(params[:trans_uuid]) if !results.empty? record = results.map { |res| res.attributes.symbolize_keys } @record = Record.replace_nil(record) # this calls method in Model else

问题 When I attempt to import a .csv comma-delimited flat file into a Microsoft SQL server 2008R2 64-bit instance , for string columns a NULL in the original data becomes a literal string "NULL" and in a numeric column I receive an import error. Can anyone please help??? 回答1: Put the data into a staging table and then insert to the production table using SQL code. update table1 set field1 = NULL where field1 = 'null' Or if you want to do for a lot of fields update table1 set field1 = case when

问题 When modifying data in a SQL Server database you can use either System.DBNull.Value or null to represent a NULL value. Both of these will work and will set the proper value to NULL . My question is - which of these is preferred, and why? Are there certain cases where one should be used in place of the other? 回答1: From System.DBNull.Value != null, and by testing this code: var result = (System.DBNull.Value == null); // this is always false We can see that the CLR doesn't treat them the same

问题 When modifying data in a SQL Server database you can use either System.DBNull.Value or null to represent a NULL value. Both of these will work and will set the proper value to NULL . My question is - which of these is preferred, and why? Are there certain cases where one should be used in place of the other? 回答1: From System.DBNull.Value != null, and by testing this code: var result = (System.DBNull.Value == null); // this is always false We can see that the CLR doesn't treat them the same

问题 Is there a way to get a column indicating the number of NULL fields in a row? This would be within a SELECT statement. For Example: Field1 Field2 Num_Null ----------------------- NULL "A" 1 UPDATE: I want this query so I can sort based on how many Affiliates sales there are of a given Book. So having 3 affiliates would be sorted higher than having 2, regardless of which ones. There are about seven affiliates in my database, and that's subject to grow. So any query requiring that each