大约有 43,000 项符合查询结果（耗时：0.0318秒） [XML]
Distributed sequence number generation?
...ing now.
You'll need to differentiate between sequence numbers and unique IDs that are (optionally) loosely sortable by a specific criteria (typically generation time). True sequence numbers imply knowledge of what all other workers have done, and as such require shared state. There is no easy way ...
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:
...
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...
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, ...
Python - List of unique dictionaries
...
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},...
Mysql error 1452 - Cannot add or update a child row: a foreign key constraint fails
...
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...
How to create id with AUTO_INCREMENT on Oracle?
...
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?
...
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
...
A composite pri...
JQuery to check for duplicate ids in a DOM
... to traditional ASP.NET you're a lot more responsible for creating all the ids in your generated page. ASP.NET would give you nasty, but unique ids.
...
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...