distinct

问题 I want to get distinct list from list of persons . List<Person> plst = cl.PersonList; How to do this through LINQ . I want to store the result in List<Person> 回答1: Distinct() will give you distinct values - but unless you've overridden Equals / GetHashCode() you'll just get distinct references . For example, if you want two Person objects to be equal if their names are equal, you need to override Equals / GetHashCode to indicate that. (Ideally, implement IEquatable<Person> as well as just

问题 How can I select and don't show duplicates? Actually, it's showing like that: apple | apple | apples | apple This is my code: $search = $_GET['q']; $query = "SELECT * FROM query WHERE searchquery LIKE '%$search%' AND searchquery <> '$search'"; 回答1: You already said the magic word: DISTINCT. SELECT DISTINCT columnname FROM query WHERE .... Note that it probably won't work if you use SELECT DISTINCT * because when you select * that means select all columns, including columns which have a unique

问题 How can I select and don't show duplicates? Actually, it's showing like that: apple | apple | apples | apple This is my code: $search = $_GET['q']; $query = "SELECT * FROM query WHERE searchquery LIKE '%$search%' AND searchquery <> '$search'"; 回答1: You already said the magic word: DISTINCT. SELECT DISTINCT columnname FROM query WHERE .... Note that it probably won't work if you use SELECT DISTINCT * because when you select * that means select all columns, including columns which have a unique

问题 I'm looking for the answer on how DISTINCT clause works in SQL (SQL Server 2008 if that makes a difference) on a query with multiple tables joined? I mean how the SQL engine handles the query with DISTINCT clause? The reason I'm asking is that I was told by my far more experienced colleague that SQL applies DISTINCT to every field of every table. It seems unlikely for me, but I want to make sure.... For example having two tables: CREATE TABLE users ( u_id INT PRIMARY KEY, u_name VARCHAR(30),

问题 I have an RDD that is too large to consistently perform a distinct statement without spurious errors (e.g. SparkException stage failed 4 times, ExecutorLostFailure, HDFS Filesystem closed, Max number of executor failures reached, Stage cancelled because SparkContext was shut down, etc.) I am trying to count distinct IDs in a particular column, for example: print(myRDD.map(a => a._2._1._2).distinct.count()) is there an easy, consistent, less-shuffle-intensive way to do the command above,

问题 I need to take hql that is currently : select distinct a from Asset as a where ... and change it to select new com.org.AssetDTO(a.id, a.address, a.status) from Asset as a where ... My problem is with the distinct keyword. Where does it belong in an hql query where you're using the new Object query type. One thought was to use a sub-select and have my distinct there. I've tried adding distinct a.id but that doesn't work. 回答1: Ok for anyone interested the proper syntax is select distinct new

问题 I need to take hql that is currently : select distinct a from Asset as a where ... and change it to select new com.org.AssetDTO(a.id, a.address, a.status) from Asset as a where ... My problem is with the distinct keyword. Where does it belong in an hql query where you're using the new Object query type. One thought was to use a sub-select and have my distinct there. I've tried adding distinct a.id but that doesn't work. 回答1: Ok for anyone interested the proper syntax is select distinct new

问题 Consider the following example of mongo collection: {"_id" : ObjectId("4f304818884672067f000001"), "hash" : {"call_id" : "1234"}, "something" : "AAA"} {"_id" : ObjectId("4f304818884672067f000002"), "hash" : {"call_id" : "1234"}, "something" : "BBB"} {"_id" : ObjectId("4f304818884672067f000003"), "hash" : {"call_id" : "1234"}, "something" : "CCC"} {"_id" : ObjectId("4f304818884672067f000004"), "hash" : {"call_id" : "5555"}, "something" : "DDD"} {"_id" : ObjectId("4f304818884672067f000005"),

问题 I have the following query: select carBrand, carYear, carModel from cars; what I want is to get only different car names. I wrote this, but it is not what i want. select DISTINCT carBrand, carYear, carModel from Cars; how can I solve this problem? 回答1: try SELECT carBrand , carYear ,carModel FROM Cars GROUP BY carBrand , carYear ,carModel; 回答2: DISTINCT works on the entire row, not a specific column. If you want to get the unique names, select only that column. SELECT DISTINCT carBrand FROM

问题 I have the following linq expression: AgentsFilter = new BindableCollection<NameValueGuid>(( from firstEntry in FirstEntries select new NameValueGuid { Name = firstEntry.Agent, Value = firstEntry.AgentId }).Distinct() ); But because of some reason, the AgentsFilter Collection is full of duplicates. What is wrong with my Distinct() ? 回答1: Distinct will use the Equals method on NameValueGuid to find duplicates. IF you do not override Equals , then it will check references. You can add an extra