Mysql Order Group

MySQL has become one of the most widely used databases in the current network, especially in Web applications, which occupy the absolute advantage of small and medium applications. It all stems from its compact, safe, efficient, open licensing and multi-platform, and, more important, the perfect combination of--php with one of the three web languages. Unfortunately, a default installation of MySQL, because the root password is empty and the program vulnerabilities caused by the overflow, so that the installation of MySQL server is a frequent target. What is more serious is that the database is often destroyed after the attack, causing disaster easily ...

First, the importance of the index The index is used to quickly find a column in a particular value of the line. Instead of using an index, MySQL must start with the first record and then read the entire table until it finds the relevant row. The larger the table, the more time it takes. If the table in the query column index, MySQL can quickly reach a location to search the middle of the data file, there is no need to see all the data. Note that if you need to access most of the rows, sequential reads are much faster since we avoid disk searches. If you use Xinhua Dictionary to find "Zhang" the Chinese characters, do not use the directory, then ...

1, use the index to traverse the table faster. The index created by default is a non-clustered index, but sometimes it is not optimal. Under non-clustered indexes, the data is physically stored on the data page. Reasonable index design should be based on the analysis and prediction of various inquiries. In general: a. There are a large number of duplicate values, and often range query (>, <,> =, <=) and order by, group by occurred columns, consider the establishment of cluster index; Column, and each column contains duplicate values ​​can be ...

1, use the index to traverse the table faster. The index created by default is a non-clustered index, but sometimes it is not optimal. Under non-clustered indexes, the data is physically stored on the data page. Reasonable index design should be based on the analysis and prediction of various inquiries. In general: a. A large number of duplicate values, and often range query (>, <,> =, <=) and order by, group by occurred column, consider the establishment of cluster index; b. Column, ...

In this lesson, we want to learn how to increase the intelligent processing capacity of the Web page. Basic functions Welcome to the third and final lesson of this tutorial. If you've learned the first and second lessons, you've mastered the basics of installing and programming MySQL and PHP. Here are some of the other functions of PHP that might be useful to you and make your development process simpler. 　　First, let's look at the document. You should know some basic concepts of the header file, right? The header file is an external file whose contents are included in the main program. ...

I now need to remove the latest content from each category as follows: select * from test group by category_id order by `date` The result is as follows. This is not the data I want, because msyql has the order of execution is the order of reference write: select ... from ... where .... group by ... having ... order by .. Execution order: ...

MySQL large table repeated fields should be how to find it? This is a lot of people have encountered the problem, here is to teach you a MySQL table repeated fields of inquiry, for your reference. The database has a large table, you need to find the name of the duplicate record id, in order to compare. If only to find the name of the database does not repeat the field, it is easy SELECT min (`id`),` name` FROM `t ...

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In recent years, with the continuous innovation and development of the Internet industry, batch after group of websites or be eliminated or stand out, for those successful websites, most of them already exist nearly 10 or more than 10 years, in such a long period of development, in addition to the business facing the challenges, Technically, it's also a lot of challenges. The following selected Alexa rankings of the previous site (ranking up to April 21, 2012, by analyzing how they are technically coping with the challenges of business development process, to a deeper understanding of the development of the Internet industry in recent years. ...