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MySQL select one column DISTINCT, with corresponding other columns
...STINCT results from the FirstName column, but I need the corresponding ID and LastName .
12 Answers
...
How to create an object for a Django model with a many to many field?
...e_object.users.add(1,2)
Update: After reading the saverio's answer, I decided to investigate the issue a bit more in depth. Here are my findings.
This was my original suggestion. It works, but isn't optimal. (Note: I'm using Bars and a Foo instead of Users and a Sample, but you get the idea).
ba...
Does MongoDB's $in clause guarantee order
...y have two options.
So let's say that you were matching on the values of _id in your documents with an array that is going to be passed in to the $in as [ 4, 2, 8 ].
Approach using Aggregate
var list = [ 4, 2, 8 ];
db.collection.aggregate([
// Match the selected documents by "_id"
{...
How do I perform the SQL Join equivalent in MongoDB?
... The new $lookup operator added to the aggregation pipeline is essentially identical to a left outer join:
https://docs.mongodb.org/master/reference/operator/aggregation/lookup/#pipe._S_lookup
From the docs:
{
$lookup:
{
from: <collection to join>,
localField: <fiel...
How to UPSERT (MERGE, INSERT … ON DUPLICATE UPDATE) in PostgreSQL?
...em in useful detail.
In general you must choose between two options:
Individual insert/update operations in a retry loop; or
Locking the table and doing batch merge
Individual row retry loop
Using individual row upserts in a retry loop is the reasonable option if you want many connections concurre...
How to implement Android Pull-to-Refresh
In Android applications such as Twitter (official app), when you encounter a ListView, you can pull it down (and it will bounce back when released) to refresh the content.
...
Retrieving the last record in each group - MySQL
..._messages AS (
SELECT m.*, ROW_NUMBER() OVER (PARTITION BY name ORDER BY id DESC) AS rn
FROM messages AS m
)
SELECT * FROM ranked_messages WHERE rn = 1;
Below is the original answer I wrote for this question in 2009:
I write the solution this way:
SELECT m1.*
FROM messages m1 LEFT JOIN mes...
How to filter SQL results in a has-many-through relation
...fe data.)
Slight diversion from the naming schema in the question: student.id is student.stud_id and club.id is club.club_id here.
I named the queries after their author in this thread, with an index where there are two.
I ran all queries a couple of times to populate the cache, then I picked the be...
MySQL Insert into multiple tables? (Database normalization?)
...s (username, password)
VALUES('test', 'test');
INSERT INTO profiles (userid, bio, homepage)
VALUES(LAST_INSERT_ID(),'Hello world!', 'http://www.stackoverflow.com');
COMMIT;
Have a look at LAST_INSERT_ID() to reuse autoincrement values.
Edit: you said "After all this time trying to figure it ...
What is the difference between save and insert in Mongo DB?
...s essentially the same.
save behaves differently if it is passed with an "_id" parameter.
For save, If the document contains _id, it will upsert querying the collection on the _id field, If not, it will insert.
If a document does not exist with the specified _id value, the save() method performs an...