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MySQL和MongoDB设计实例进行对比 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...查询：
db.getCollection("mobiles").find({
"params": {
$all: [
{$elemMatch: {"name": "待机时间", "value": {$gt: 100}}},
{$elemMatch: {"name": "外观设计", "value": "直板"}}
]
}
});
注：查询中用到的$all，$elemMatch等高...
Linux MySql编译安装 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...d mysql
useradd -g mysql mysql
#开始编译安装
cmake -DCMAKE_INSTALL_PREFIX=/usr/local/mysql \
-DMYSQL_UNIX_ADDR=/tmp/mysql.sock \
-DDEFAULT_CHARSET=utf8 \
-DDEFAULT_COLLATION=utf8_general_ci \
-DWITH_EXTRA_CHARSETS=all \
-DWITH_MYISAM_STORAGE_ENGINE=1 \
-DWITH_INNOBASE_STORAGE_ENGIN...
What is the performance cost of having a virtual method in a C++ class?
...3ghz in-order PowerPC processor. On that architecture, a virtual function call costs 7 nanoseconds longer than a direct (non-virtual) function call.
So, not really worth worrying about the cost unless the function is something like a trivial Get()/Set() accessor, in which anything other than inli...
How do I convert seconds to hours, minutes and seconds?
...the decimal seconds.
– CPBL
Nov 27 '16 at 19:43
1
...
Can't open config file: /usr/local/ssl/openssl.cnf on Windows [duplicate]
...'t fix the issue.
– birken25
Apr 4 '16 at 20:20
3
Does not work and I've checked the OPENSSL_CONF...
Failed to load JavaHL Library
...pdate site...
– Cerin
Mar 13 '14 at 16:27
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How do I read / convert an InputStream into a String in Java?
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answered Nov 21 '08 at 16:54
Harry LimeHarry Lime
27.5k44 gold badges2626 silver badges3333 bronze badges
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Rails: fields_for with index?
... of 10+......!
– user5084534
Oct 7 '16 at 12:04
1
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Convert Python dict into a dataframe
...
The error here, is since calling the DataFrame constructor with scalar values (where it expects values to be a list/dict/... i.e. have multiple columns):
pd.DataFrame(d)
ValueError: If using all scalar values, you must must pass an index
You could ...
What's the best way to trim std::string?
I'm currently using the following code to right-trim all the std::strings in my programs:
46 Answers
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