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Detailed explanation of the use of linux awk command

This article introduces the detailed explanation of the use of Linux awk command. I hope it can help everyone.

Dec 13, 2016 am 09:51 AM

awk command

Thoughts triggered by a distinct question

The data here has the following characteristics: in one DepartmentId, there may be multiple Names, and vice versa. That is to say, Name and DepartmentId have a many-to-many relationship. Now I want to implement such a query: after sorting by DepartmentID (the first step), then obtain the unique values ??of the Name column (the second step), and retain the relative order after the first step. In this example, the three values ??that should be returned are: ACB

Dec 13, 2016 am 09:45 AM

distinct

Oracle-distinct usage

The distinct keyword is used to filter out redundant duplicate records and keep only one, but it is often only used to return the number of unique records, rather than using it to return all values ??of non-duplicate records. The reason is that distinct can only be solved by double loop query, which will undoubtedly directly affect the efficiency of a website with a very large amount of data.

Dec 13, 2016 am 09:33 AM

Usage of distinct in SQL (analysis of four examples)

The distinct keyword is used to filter out redundant duplicate records and keep only one, but it is often only used to return the number of unique records, rather than using it to return all values ??of non-duplicate records. The reason is that distinct can only return its target field, but cannot return other fields. Next, I will share with you the usage of distinct in SQL through this article. Friends who need it can refer to it.

Dec 13, 2016 am 09:31 AM

distinct

Usage of distinct in SQL

Tables may contain duplicate values. This is not a problem, but sometimes you may want to just list distinct values. The keyword distinct is used to return uniquely distinct values.

Dec 13, 2016 am 09:25 AM

distinct

Use ajaxFileUpload for image upload

Using ajaxFileUpload is mainly to upload files asynchronously, without opening a new page for uploading! Since segmentfault cannot upload files, the code of the file ajaxFileUpload.js is at the bottom of this article: Since the file ajaxFileUpload has not been updated for a long time, handleError: function(s, xhr, status, e) has been added to handle errors. ,

Dec 12, 2016 pm 05:47 PM

ajaxfileupload

AjaxFileUpload implements asynchronous file upload (AjaxFileUpload.js file download and parameter introduction)

AjaxFileUpload achieves better asynchronous file upload effect

Dec 12, 2016 pm 05:38 PM

ajaxfileupload

ajaxFileUpload asynchronous file upload simple to use

Dec 12, 2016 pm 05:33 PM

ajaxfileupload

jQuery plug-in ajaxFileUpload

ajaxFileUpload.js There are many names with the same name, because it is easy to make one.

Dec 12, 2016 pm 05:29 PM

ajaxfileupload

The difference between strings and arrays in C language

The elements of an array can be of any type, and a string is a special type of array that uses a well-known rule for determining its length. There are two types of languages, those that treat strings simply as an array of characters and those that treat strings as a special type. C belongs to the former category, but there is one addition, that is, the C string is terminated with a NUL character. The value of an array is the same as the address of the first element in the array (or a pointer to that element), so generally a C string and a character pointer are equivalent.

Dec 12, 2016 pm 05:25 PM

string array

The difference between string pointer and character array

Both character arrays and character pointer variables can be used to store and operate strings. But there is a difference between the two. You should pay attention to the following issues when using it:

Dec 12, 2016 pm 05:22 PM

string array

Detailed explanation of the use of character arrays and strings in C language

Definition and initialization of character array The easiest way to understand the initialization of character array is to assign characters to each element in the array one by one.

Dec 12, 2016 pm 05:17 PM

string array