difference

问题 I have the following query : SELECT SUM(P_QTY) FROM rankhistory WHERE P_ID= '1' AND RH_DATE>=1438556400 AND RH_DATE<1438642800 The above query returns 268 The result set contains two elements of P_QTY which are 160 and 108 Now what I want is be able to receive the difference instead of the sum, so what I want my query to return is 52 , how can I achieve that through sql query? Please note that the subquery can return more than one result, and the intended is get the total change. For example

问题 quick simple question In the following example of an external CSS page; body { background-image: url(background.jpg); } header { background: url(background.jpg); } I understand they are effecting different element selectors, my question is what is the difference between using background vs background-image? Does one have access to specific attributes to the other? Please and thank you. 回答1: In a background property you can add background-color , repeat , no-repeat and other image attributes,

问题 What are the differences between ComboBox and ChoiceBox in JavaFX? I'm not entirely clear on that just from the Javadoc for both classes. At the end of the day, I need a dropdown control that can be repopulated dynamically at runtime (I've got a database on the backend). For all cases in my application, I only need to select one item from the dropdown menus. The user also shouldn't be able to add an option to the dropdown menu from the screens they are visible on. My understanding is that

问题 Here is my example. I am reading the following file: sample_data library(dplyr) txt <- c('"", "MDN", "Cl_Date"', '"1", "A", "2017-04-15 15:10:42.510"', '"2", "A", "2017-04-01 14:47:23.210"', '"3", "A", "2017-04-01 14:49:54.063"', '"4", "B", "2017-04-30 13:25:00.000"', '"5", "B", "2017-04-03 17:53:13.217"', '"6", "B", "2017-04-15 15:17:43.780"') ts <- read.csv(text = txt, as.is = TRUE) ts$Cl_Date <- as.POSIXct(ts$Cl_Date) ts <- ts %>% group_by(MDN) %>% arrange(Cl_Date) %>% mutate(time_diff = c

问题 I have been reading Android documentation (AsyncTask, Thread) and vogella tutorial about this matter, but I have doubts yet. For example, I want to send a message from an Android app to a server. And I would like this process to be responsive. What should I use? I have seen examples where they create a new Thread for not block UI, but this way we don't have the progress of process, also you have to process the response within the Thread because the run() method doesn't returning anything.

问题 On choosing Data Source under ODBC (64-Bit) on Windows, i get two available options of MySQL Database: MySQL ODBC 5.3 ANSI Driver MySQL ODBC 5.3 Unicode Driver What are the difference between these two? 回答1: Firstly I should say that I don't use MySQL but I do know about ODBC Drivers. In ODBC there are different APIs for unicode and ansi. The ansi APIs end in A and the unicode APIs end in W (e.g., SQLPrepareA and SQLPrepareW). The ansi APIs accept bytes/octets for character strings and hence

问题 On choosing Data Source under ODBC (64-Bit) on Windows, i get two available options of MySQL Database: MySQL ODBC 5.3 ANSI Driver MySQL ODBC 5.3 Unicode Driver What are the difference between these two? 回答1: Firstly I should say that I don't use MySQL but I do know about ODBC Drivers. In ODBC there are different APIs for unicode and ansi. The ansi APIs end in A and the unicode APIs end in W (e.g., SQLPrepareA and SQLPrepareW). The ansi APIs accept bytes/octets for character strings and hence

问题 Are there are differences between hashmap and hashtable in theory? I don't mean in the concrete definitions given in Java (or the implementation), but in theory. Isn't a hashtable a map that uses hashing ... hence a hashmap? 回答1: According to Wikipedia, they are the same: In computing, a hash table (hash map) is a data structure used to implement an associative array (...) According to Wikibooks, it's the same: A hash table, or a hash map, is a data structure that associates keys with values.

问题 As per my research, there is a significant difference in the concept of backstack and how they exist: Activity When an activity is placed to the backstack of activities the user can navigate back to the previous activity by just pressing the back button. Activity can exist independently. Fragment When an fragment is placed to the activity we have to request the instance to be saved by calling addToBackstack() during the fragment transaction . Fragment has to live inside the activity Are there

问题 As per my research, there is a significant difference in the concept of backstack and how they exist: Activity When an activity is placed to the backstack of activities the user can navigate back to the previous activity by just pressing the back button. Activity can exist independently. Fragment When an fragment is placed to the activity we have to request the instance to be saved by calling addToBackstack() during the fragment transaction . Fragment has to live inside the activity Are there