what circumstances are indexes, but not used?Indexes do not always take effect, such as the following, which will invalidate the index :
If there is or in the condition, even if some of the conditions in the index are not used ( which is why the use of or
]-Qa time.
If there are any mistakes in the above blog posts or you have any questions, opinions, and suggestions about this ID blog, please give me feedback in time. Thank you for reading this article.
What is redis?
Generally, there are several types of databases, including SQL/nsql, relational databases, and key-value databases, redis is also a key-value da
What is annotation, how to use annotation, why is annotation used, and why is annotation used
Annotation
Annotation can be seen as an extension template for a class/method. Each class/method i
array to get the character array.
Let's explain the problem of the subject.
I did the same experiment in the default terminal of ubuntu kylin Chinese environment, but the result is exactly the opposite to that of the subject:
See no?
Neither the subject nor I lie. Why?
Because
Unicode ("Chinese character", "gb2312 ")I think the key is to distinguish between the concept of "Byte" and "character",
What is PHP used ?, Is PHP used?
To master PHP is to use computers to develop rules. Framework tp3.2/5.2
In Structured Programming, programs are designed around the tasks to be solved.
In object-oriented programming, the progra
source (such as Twitter Bootstrap). I personally think that SAP can do more to make SAPUI5 a lot of attention, open it up or promote it outside of the traditional SAP technology conference. I recently attended some developers and web developers meetings in Australia, and unfortunately there is no sap in these events. Currently, there is a fierce competition (eg) in wha
What do you call office software?
The word office automation is very familiar to everyone, its English name is office automation, abbreviation OA. In the early 80, when the domestic computer technology increasingly popular, office automation is almost synonymous with computer applications, many units or individuals to
Just like what is the difference between the following code {code...} and {code? Humbly ask the experts for advice, just like
The following code
Echo 'configuration error'; exit (3); // Status 3 indicates exit due to configuration error
And
// Exit directly ('configuration error ');
What is the difference?
I would lik
What is polymorphism.
Concept: The same operation acts on different objects, can have different interpretations, produce different execution results, this is polymorphism. Simply put: the reference to the base class refers to the object of the subclass.
Why use polymorphism?
Reason: We know that encapsulation can hide implementation details, making code modular,
higher the version, the more security is usually better.
What's the use of IIS?
About the role of IIS and some of the friends used are web site technicians or webmaster, for ordinary computer users, so we can see that the normal installation of the XP/WIN7/WIN8 system does not have IIS functionality, mainly because IIS is useless to ordinary users, was castrat
What is the server used? Can data be saved? So what is the difference with the database? For example, the user's profile picture is stored on the server. I don't know what the server
What is the role of the hook function in thinkphp? What business logic is generally used for processing?
Reply content:
What is the role of the hook function in thinkphp?
(){
}Public Person (driver Driver ){This. Driver = driver;}Public void drive (){Driver. Run ();}Public void setdriver (driver Driver) {// using parameter polymorphism, you can buy any car in the futureThis. Driver = driver;}
Public static void main (string ARGs []) {Person P = new person ();JD = new JD (); // buy a JD if you have no money at the beginningP. setdriver (JD );P. Driver ();Benz = new Benz {(); // you have money to change your car.P. setdriver (Benz );P. Driver ();}}
In Linux, you often use CTRL and other key combinations, which are commonly used and what is the meaning of it?
CTRL + C ends a running program
Ctrl+d end input or exit shell
Ctrl+s Pause Screen Output "Lock terminal"
Ctrl+q restore screen output "unlock terminal"
Ctrl+l clear screen, "lowercase letter
With the current in our lives in the role of more and more obvious, many enterprises have tried water marketing, mode for a stubble and another stubble, but can not find a good way, powder mother flow platform with you detailed introduction of what is easy to do marketing.Now the most commonly used on the market is Tho
Simple examples are used to understand what machine learning is, and examples are used to understand machine learning.
1. What is machine learning?
What
Baidu question:For example, there is a string type 3To convert it to the int type, use (INT) 3.Or use convert. toint32 (3 );Or can both be used. Why?
Best Answer:
First of all, I want to point out that in C #, Int Is Actually system. int32, that is, all are 32-bit.
Second, (INT) and convert. toint32 are two diffe
What is a resource table? In addition, after the space is set to public, the direct domain name key can be accessed. Why should I use the QiniuRSMakeBaseUrl function in phpsdk? What is a resource table? In addition, after the space is
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