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MySQL: What's the difference between float and double?
...00002 | 1.6900000000 |
This is using MySQL 6.7
Query:
SELECT
float_1 + float_2 as 'float add',
double_1 + double_2 as 'double add',
decimal_1 + decimal_2 as 'decimal add',
float_1 * float_2 as 'float multiply',
double_1 * double_2 as 'double multiply',
decimal_1 * decim...
Django select only rows with duplicate field values
...values('name')
.annotate(Count('id'))
.order_by()
.filter(id__count__gt=1)
This is as close as you can get with Django. The problem is that this will return a ValuesQuerySet with only name and count. However, you can then use this to construct a regula...
From an array of objects, extract value of a property as array
...
Check out Lodash's _.pluck() function or Underscore's _.pluck() function. Both do exactly what you want in a single function call!
var result = _.pluck(objArray, 'foo');
Update: _.pluck() has been removed as of Lodash v4.0.0, in favour of _...
How to do relative imports in Python?
...answering the question.
The problem is that you're running the module as '__main__' by passing the mod1.py as an argument to the interpreter.
From PEP 328:
Relative imports use a module's __name__ attribute to determine that module's position in the package hierarchy. If the module's name does...
Why does Python use 'magic methods'?
...s', e.g. to make its length available, an object implements a method, def __len__(self) , and then it is called when you write len(obj) .
...
Elastic Search: how to see the indexed data
...Search and Rails, where some data was not indexed properly because of attr_protected. Where does Elastic Search store the indexed data? It would be useful to check if the actual indexed data is wrong.
...
Python Linked List
...tains a cargo object and a reference to a linked list.
class Node:
def __init__(self, cargo=None, next=None):
self.car = cargo
self.cdr = next
def __str__(self):
return str(self.car)
def display(lst):
if lst:
w("%s " % lst)
display(lst.cdr)
else:
w("nil\n")
...
sql “LIKE” equivalent in django query
...
Use __contains or __icontains (case-insensitive):
result = table.objects.filter(string__contains='pattern')
The SQL equivalent is
SELECT ... WHERE string LIKE '%pattern%';
...
Get event listeners attached to node using addEventListener
... 'old' prototype methods):
var ListenerTracker=new function(){
var is_active=false;
// listener tracking datas
var _elements_ =[];
var _listeners_ =[];
this.init=function(){
if(!is_active){//avoid duplicate call
intercep_events_listeners();
}
...
OceanBase使用libeasy原理源码分析：服务器端 - 数据库(内核) - 清泛网 - ...
...、OceanBase启动时的使用模式
二、 基础数据结构
2.1 easy_list_t
2.2 easy_pool_t
2.3 easy_buf_t
2.4 easy_connection_t
三、 连接建立
四、 同步处理(OceanBase少量使用这种模式)
五、 异步处理(OceanBase大量采用这种模式)
六、 资源管理
...