distinct

I can perform the following SQL Server selection of distinct (or non-repeating names) from a column in one table like so: SELECT COUNT(DISTINCT [Name]) FROM [MyTable] But what if I have more than one table (all these tables contain the name field called [Name]) and I need to know the count of non-repeating names in two or more tables. If I run something like this: SELECT COUNT(DISTINCT [Name]) FROM [MyTable1], [MyTable2], [MyTable3] I get an error, "Ambiguous column name 'Name'". PS. All three tables [MyTable1], [MyTable2], [MyTable3] are a product of a previous selection. After the

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I have a MySQL query that results in something like this: person | some_info ================== bob | pphsmbf24 bob | rz72nixdy bob | rbqqarywk john | kif9adxxn john | 77tp431p4 john | hx4t0e76j john | 4yiomqv4i alex | n25pz8z83 alex | orq9w7c24 alex | beuz1p133 etc... (This is just a simplified example. In reality there are about 5000 rows in my results). What I need to do is go through each person in the list (bob, john, alex, etc...) and pull out a row from their set of results. The row I pull out is sort of random but sort of also based

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I'm a newbie to Apache Spark and was learning basic functionalities. Had a small doubt.Suppose I have an RDD of tuples (key, value) and wanted to obtain some unique ones out of them. I use distinct() function. I'm wondering on what basis does the function consider that tuples as disparate..? Is it based on the keys, or values, or both? 回答1: .distinct() is definitely doing a shuffle across partitions. To see more of what's happening, run a .toDebugString on your RDD. val hashPart = new HashPartitioner( ) val myRDDPreStep = val myRDD =

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: Possible Duplicate: Inherit interfaces which share a method name I have two base classes I1 and I2 with pure virtual functions void R() = 0; . I want the derived class IImpl to inherit from I1 and I2 and to have distinct implementations for I1::R() and I2::R() . The code below compiles and works in MS VS 2005 and 2010. I compile with Language Extension disabled and on warning level 4. There are no warnings and no errors. I tried the same code in gcc 4.2. It does not compile. GCC reports an error: error: cannot define member function 'I1::R'

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I would like to do this but with the criteria API instead: select count(distinct e) from Event e, IN(e.userAccessPermissions) p where p.principal = :principal and p.permission in (:permissions) Any ideas? 回答1: You can use countDistinct on CriteriaBuilder criteriaQuery.select(criteriaBuilder.countDistinct(entityRoot)) 回答2: Like this? Criteria crit = session.createCriteria(Event.class): crit.createAlias("userAccessPermissions", "p"); crit.add(Restrictions.eq("p.principal", principal); crit.add(Restrictions.in("p.permission", permissions); crit

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I am using pymongo and want to have distinct values for a field such that I can also pass other query parameters. For example, I have entries like: { id = "my_id1" tags: [tag1, tag2, tag3], category: "movie", } { id = "my_id2" tags: [tag3, tag6, tag9], category: "tv", } { id = "my_id3" tags: [tag2, tag6, tag8], category: "movie", } So I want to have all distinct tags under movie category. Can anyone please guide how can I achive this using pymongo. In mongo javascript shell, I issued db.mycoll.distinct('tags', {category: "movie"}) and it

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: Given a linq expression of an object collection 'items' such as this: var total = (from item in items select item.Value).Distinct().Count() Is it possible to convert this to use linq functions/lambdas: items.Select(???).Distinct().Count() 回答1: Use this: items.Select(i => i.Value).Distinct().Count() 回答2: It must be possible, since behind the scenes, LINQ is translated to lambdas and expression trees (at least LINQ to objects) In your case the ??? part would be item => item.Value , i.e. for item , output item.value . So, the whole expression

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I am trying to find a MySQL query that will find distinct values in a particular field, count the number of occurrences of that value and then order the results by the count. example db id name ----- ------ 1 Mark 2 Mike 3 Paul 4 Mike 5 Mike 6 John 7 Mark expected result name count ----- ----- Mike 3 Mark 2 Paul 1 John 1 Thanks 回答1: SELECT name,COUNT(*) as count FROM tablename GROUP BY name ORDER BY count DESC; 回答2: what about something like this : select name, count(*) as num from your_table group by name order by count(*) desc ie, you are

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: How can I make an order_by like this .... p = Product.objects.filter(vendornumber='403516006')\ .order_by('-created').distinct('vendor__name') The problem is that I have multiple vendors with the same name, and I only want the latest product by the vendor .. Hope it makes sense? I got this DB error: SELECT DISTINCT ON expressions must match initial ORDER BY expressions LINE 1: SELECT DISTINCT ON ("search_vendor"."name") "search_product"... 回答1: Based on your error message and this other question , it seems to me this would fix it: p =