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How to select a single field for all documents in a MongoDB collection?
...ery. In the result set, only the item and qty fields and, by default, the _id field return in the matching documents.
db.inventory.find( { type: 'food' }, { item: 1, qty: 1 } )
In this example from the folks at Mongo, the returned documents will contain only the fields of item, qty, and _id.
Thus,...
SQL JOIN and different types of JOINs
... @KNU The w3fools should give credit from where they have taken the idea for the pictures. See A visualization of SQL joins by Jeff Atwood (yes, the one who co-authored SO) and the linked article by Ligaya Turmelle where Jeff got the idea and explanded it.
– ypercubeᵀ...
Passing an array to a query using a WHERE clause
Given an array of ids $galleries = array(1,2,5) I want to have a SQL query that uses the values of the array in its WHERE clause like:
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Find all records which have a count of an association greater than zero
... To remove the duplicates, use
Project.joins(:vacancies).group('projects.id')
UPDATE:
As pointed out by @Tolsee, you can also use distinct.
Project.joins(:vacancies).distinct
As an example
[10] pry(main)> Comment.distinct.pluck :article_id
=> [43, 34, 45, 55, 17, 19, 1, 3, 4, 18, 44, ...
Mysql error 1452 - Cannot add or update a child row: a foreign key constraint fails
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Quite likely your sourcecodes_tags table contains sourcecode_id values that no longer exists in your sourcecodes table. You have to get rid of those first.
Here's a query that can find those IDs:
SELECT DISTINCT sourcecode_id FROM
sourcecodes_tags tags LEFT JOIN sourcecodes sc ON...
Python - List of unique dictionaries
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So make a temporary dict with the key being the id. This filters out the duplicates.
The values() of the dict will be the list
In Python2.7
>>> L=[
... {'id':1,'name':'john', 'age':34},
... {'id':1,'name':'john', 'age':34},
... {'id':2,'name':'hanna', 'age':30},...
How to create id with AUTO_INCREMENT on Oracle?
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There is no such thing as "auto_increment" or "identity" columns in Oracle as of Oracle 11g. However, you can model it easily with a sequence and a trigger:
Table definition:
CREATE TABLE departments (
ID NUMBER(10) NOT NULL,
DESCRIPTION VARCHAR2(50) ...
How to map a composite key with JPA and Hibernate?
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To map a composite key, you can use the EmbeddedId or the IdClass annotations. I know this question is not strictly about JPA but the rules defined by the specification also applies. So here they are:
2.1.4 Primary Keys and Entity Identity
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A composite pri...
Would it be beneficial to begin using instancetype instead of id?
Clang adds a keyword instancetype that, as far as I can see, replaces id as a return type in -alloc and init .
4 An...
How do I add a Fragment to an Activity with a programmatically created content view
...han one problem with that code. A fragment cannot be declared that way, inside the same java file as the activity but not as a public inner class. The framework expects the fragment's constructor (with no parameters) to be public and visible. Moving the fragment into the Activity as an inner class, ...