unique

问题 I'm trying to create a table that would enforce a unique combination of two columns of the same type - in both directions. E.g. this would be illegal: col1 col2 1 2 2 1 I have come up with this, but it doesn't work: database=> \d+ friend; Table "public.friend" Column | Type | Modifiers | Storage | Stats target | Description --------------+--------------------------+-----------+----------+--------------+------------- user_id_from | text | not null | extended | | user_id_to | text | not null |

问题 Given a list of tuples like so: a = [ ( "x", 1, ), ( "x", 2, ), ( "y", 1, ), ( "y", 3, ), ( "y", 4, ) ] What would be the easiest way to filter for unique first element and merge the second element. An output like so would be desired. b = [ ( "x", 1, 2 ), ( "y", 1, 3, 4 ) ] Thanks, 回答1: You can use a defaultdict: >>> from collections import defaultdict >>> d = defaultdict(tuple) >>> a = [('x', 1), ('x', 2), ('y', 1), ('y', 3), ('y', 4)] >>> for tup in a: ... d[tup[0]] += (tup[1],) ... >>>

问题 How do I return all the unique words from a text file using Python? For example: I am not a robot I am a human Should return: I am not a robot human Here is what I've done so far: def unique_file(input_filename, output_filename): input_file = open(input_filename, 'r') file_contents = input_file.read() input_file.close() word_list = file_contents.split() file = open(output_filename, 'w') for word in word_list: if word not in word_list: file.write(str(word) + "\n") file.close() The text file

问题 I have not found any answer regarding my question, all unique constraint questions did not involve MS Access. The question is how to make a unique constraint on multpile fields in MS Access 2003 database? If my table consists of columns id, A, B, C, D, E, F . I have an index on column id , but I would like to have a unique constraint set on both columns A and B . Hence, I may have a duplicate value in column A , provided the value in column B are different. I want to stress that I am not

问题 Using session.load() or session.get() or any other method of org.hibernate.session , is it possible to get a record in hibernate based on the Unique column rather than the PK column value? My requirement is that I need to get the records based on the unique column value and not the primary key. It is like I don want to use the Criteria API. I need to use the session.get or load kind of methods. The answer that you have mentioned is for doing a search. But I am asking for getting a single

问题 In the past I have made a function that generates an unique id (number) from a string. Today I discover that it is not as unique as should be. Never saw a problem before with it. Today two different inputs generates the same id (number). I use the same technique in Delphi, C++, PHP and Javascript to generate the same id's so there is no difference when different languages are involved to a project. For example this can be handy to communicate, for HTML id's, tempfiles etc. In general, what I

问题 i always use this commmand line to sort and get uniq lines only and it works as a charm even with large files (over 500,000 lines) sort filename.txt | uniq | sponge filename.txt shortest equivalent python code would be f = open("filename.txt", "r") lines = [line for line in f] lines = lines.sort() lines = set(lines) but of course this is not scalable because of memory constrains and writing scalable code in python would take time , so i wonder what is the shortest equivalent code (package) in

问题 I'm working on message system and I need to get last message from each user who sent message to logged user. I have this structure in mongoDB: [{ "_id": "551bd621bb5895e4109bc3ce", "from": "admin", "to": "user1", "message": "message1", "created": "2015-04-01T11:27:29.671Z" }, { "_id": "551bd9acf26208ac1d9b831d", "from": "user1", "to": "admin", "message": "message2", "created": "2015-04-01T11:42:36.936Z" }, { "_id": "551bdd6d849d53001dd8a64a", "from": "user1", "to": "user2", "message":

问题 This question already has answers here : How do I specify unique constraint for multiple columns in MySQL? (11 answers) Closed 6 years ago . I have two tables --> Variables (id, name) and Variable_Entries (id, var_id, value). I want each variable to have a unique set of entries. If I make the value entry unique then a different variable won't be able to have that same value which is not right. Is there some way to make the value column unique for identical var_id's? 回答1: Yes: alter table

问题 This question already has answers here : How do I specify unique constraint for multiple columns in MySQL? (11 answers) Closed 6 years ago . I have two tables --> Variables (id, name) and Variable_Entries (id, var_id, value). I want each variable to have a unique set of entries. If I make the value entry unique then a different variable won't be able to have that same value which is not right. Is there some way to make the value column unique for identical var_id's? 回答1: Yes: alter table