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MongoDB sort排序、index索引教程 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...排列。
语法
sort()方法基本语法如下所示：
>db.COLLECTION_NAME.find().sort({KEY:1})
注意：
即使键值写错了（即文档中没有该键值），命令本身不会报错，当然排序也没有效果。
实例
col 集合中的数据如下：
{ "_id" : ObjectId("56066542...
How do I spool to a CSV formatted file using SQLPLUS?
... numbers (avoid scientific notation on IDs)
spool myfile.csv
select table_name, tablespace_name
from all_tables
where owner = 'SYS'
and tablespace_name is not null;
Output will be like:
TABLE_PRIVILEGE_MAP ,SYSTEM
SYSTEM_PRIVILEGE_MAP ,S...
What is the difference between g++ and gcc?
...as a few extra macros.
Extra Macros when compiling *.cpp files:
#define __GXX_WEAK__ 1
#define __cplusplus 1
#define __DEPRECATED 1
#define __GNUG__ 4
#define __EXCEPTIONS 1
#define __private_extern__ extern
share
...
How to change Rails 3 server default port in develoment?
..."rails" with Rails 3 gems installed from the root of your application.
APP_PATH = File.expand_path('../../config/application', __FILE__)
require File.expand_path('../../config/boot', __FILE__)
# THIS IS NEW:
require "rails/commands/server"
module Rails
class Server
def default_options
...
MD5 algorithm in Objective-C
...ons.h"
#import <CommonCrypto/CommonDigest.h> // Need to import for CC_MD5 access
@implementation NSString (MyAdditions)
- (NSString *)md5
{
const char *cStr = [self UTF8String];
unsigned char result[CC_MD5_DIGEST_LENGTH];
CC_MD5( cStr, (int)strlen(cStr), result ); // This is the m...
Delete column from SQLite table
...trate how this could be done:
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1;
CREATE TABLE t1(a,b);
INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;
...
Why can't (or doesn't) the compiler optimize a predictable addition loop into a multiplication?
...
It does now -- at least, clang does:
long long add_100k_signed(int *data, int arraySize)
{
long long sum = 0;
for (int c = 0; c < arraySize; ++c)
if (data[c] >= 128)
for (int i = 0; i < 100000; ++i)
sum += data[c];
re...
Auto layout constraints issue on iOS7 in UITableViewCell
...n the cell is reused like this:
For Static UITableViewController:
#ifdef __IPHONE_OS_VERSION_MIN_REQUIRED
#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_8_0
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [sup...
Delete files older than 15 days using PowerShell
...n the $limit.
Get-ChildItem -Path $path -Recurse -Force | Where-Object { !$_.PSIsContainer -and $_.CreationTime -lt $limit } | Remove-Item -Force
# Delete any empty directories left behind after deleting the old files.
Get-ChildItem -Path $path -Recurse -Force | Where-Object { $_.PSIsContainer -and...
ZSH complains about RVM __rvm_cleanse_variables: function definition file not found
...
searched for "whats 'zcompdump' for" while diagnosing the __rvm_cleanse_variables issue... two birds, one search. +1's to everyone.
– max
Mar 21 '15 at 18:54
...