How can I merge two maps in go?
There is no built in way, nor any method in the standard packages to do such a merge. The idomatic way is to simply iterate: for k, v := range b { a[k] = v }
union
Using union and order by clause in mysql
You can do this by adding a pseudo-column named rank to each select, that you can sort by first, before sorting by your other criteria, e.g.: select * from ( select 1 as Rank, id, add_date from Table union all select 2 as Rank, id, add_date from Table where distance < 5 union all select … Read more
Intersection and union of ArrayLists in Java
Here’s a plain implementation without using any third-party library. Main advantage over retainAll, removeAll and addAll is that these methods don’t modify the original lists input to the methods. public class Test { public static void main(String… args) throws Exception { List<String> list1 = new ArrayList<String>(Arrays.asList(“A”, “B”, “C”)); List<String> list2 = new ArrayList<String>(Arrays.asList(“B”, “C”, “D”, … Read more
How can I get the intersection, union, and subset of arrays in Ruby?
I assume X and Y are arrays? If so, there’s a very simple way to do this: x = [1, 1, 2, 4] y = [1, 2, 2, 2] # intersection x & y # => [1, 2] # union x | y # => [1, 2, 4] # difference x – y # => … Read more
How to order by with union in SQL?
Just write Select id,name,age From Student Where age < 15 Union Select id,name,age From Student Where Name like “%a%” Order by name the order by is applied to the complete resultset
What is the difference between JOIN and UNION?
UNION puts lines from queries after each other, while JOIN makes a cartesian product and subsets it — completely different operations. Trivial example of UNION: mysql> SELECT 23 AS bah -> UNION -> SELECT 45 AS bah; +—–+ | bah | +—–+ | 23 | | 45 | +—–+ 2 rows in set (0.00 sec) … Read more
What is the difference between UNION and UNION ALL?
UNION removes duplicate records (where all columns in the results are the same), UNION ALL does not. There is a performance hit when using UNION instead of UNION ALL, since the database server must do additional work to remove the duplicate rows, but usually you do not want the duplicates (especially when developing reports). To … Read more