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Can I concatenate multiple MySQL rows into one field?
...person_id, GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Ludwig stated in his comment, you can add the DISTINCT operator to avoid duplicates:
SELECT person_id, GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Jan stated i...
Why is this program erroneously rejected by three C++ compilers?
...mpiler vendor supports (canonically defined) text files: any file produced by a text editor, typically a series of characters.
Note that the C++ standard is based off the C standard (§1.1/2), and the C(99) standard says, in §1.2:
This International Standard does not specify
— the mecha...
Split Java String by New Line
...'m trying to split text in a JTextArea using a regex to split the String by \n However, this does not work and I also tried by \r\n|\r|n and many other combination of regexes.
Code:
...
rbenv not changing ruby version
...results. The following is what i get in my terminal when I try to change ruby versions:
21 Answers
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Postgresql GROUP_CONCAT equivalent?
...ld, array_agg(value_field1), array_agg(value_field2)
FROM data_table
GROUP BY id_field
array_agg returns an array, but you can CAST that to text and edit as needed (see clarifications, below).
Prior to version 8.4, you have to define it yourself prior to use:
CREATE AGGREGATE array_agg (anyeleme...
In mongoDb, how do you remove an array element by its index?
...
There is no straight way of pulling/removing by array index. In fact, this is an open issue http://jira.mongodb.org/browse/SERVER-1014 , you may vote for it.
The workaround is using $unset and then $pull:
db.lists.update({}, {$unset : {"interests.3" : 1 }})
db.lists...
What is the most efficient/elegant way to parse a flat table into a tree?
...d in the same table too. Read "Trees and Hierarchies in SQL for Smarties" by Joe Celko for a lot more information on these designs.
I usually prefer a design called Closure Table (aka "Adjacency Relation") for storing tree-structured data. It requires another table, but then querying trees is pre...
Multiple “order by” in LINQ
I have two tables, movies and categories , and I get an ordered list by categoryID first and then by Name .
7 Answers...
Reason to Pass a Pointer by Reference in C++?
...
You would want to pass a pointer by reference if you have a need to modify the pointer rather than the object that the pointer is pointing to.
This is similar to why double pointers are used; using a reference to a pointer is slightly safer than using point...
Group by in LINQ
...basically want:
var results = from p in persons
group p.car by p.PersonId into g
select new { PersonId = g.Key, Cars = g.ToList() };
Or as a non-query expression:
var results = persons.GroupBy(
p => p.PersonId,
p => p.car,
(key, g) => new { Perso...