Clustered and non-clustered indexes in SQL Server

The following is an example:

The body of our Chinese dictionary is a clustered index. For example, if we want to check the word "an", we will naturally open the first few pages of the dictionary, because the Pinyin of "an" is "", the Dictionary of Chinese characters sorted by pinyin starts with the English letter "a" and ends with "Z". Then the word "an" is naturally placed at the front of the dictionary. If you still cannot find the word in all the parts starting with "A", it means that you do not have this word in your dictionary. Similarly, if you query the word "Zhang, then you will turn your dictionary to the last part, because the Pinyin of "Zhang" is "Zhang ". That is to say, the body of the dictionary itself is a directory, and you do not need to query other directories to find the content you need.
We refer to this text content as a directory arranged according to certain rules as "clustered Index ".

If you know a word, you can quickly find it automatically. However, you may also encounter a word you do not know and do not know its pronunciation. At this time, you cannot find the word you want to query according to the method just now, you need to find the word you are looking for based on the "radicals", and then directly go to a page based on the page number after the word to find the word you are looking. However, the words you find in combination with the "radical directory" and "word checking table" are not really the sorting method of the text. For example, you can query the word "Zhang, we can see that the page number of the "Zhang" in the word checking table after the department head is 672, and the "Zhang" in the word checking table is "Chi", but the page number is 63, under "Zhang" is the word "", and the page is 390 pages. Obviously, these words are not really in the upper and lower sides of the word "Zhang, the continuous "Chi, Zhang, and "words you see are actually their sorting in the non-clustered index, which is the ing of words in the dictionary body in the non-clustered index. We can find the words you need in this way, but it requires two steps: first find the results in the directory, and then flip to the page number you need.
We refer to this directory as a directory, and the text as a non-clustered index ".

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