Use Of Distinct In Mysql

Mysql Guide sql distinct delete duplicate records How to use distinct keyword in mysql Filter the result list in a select statement Duplicate value If you want to delete duplicate data query data, you can use the distinct keyword to filter duplicate values, the following distinct usage. select distinct column_name from table_name; Let's take a look at a simple example ...

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 ...

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 ...

mysql Tutorial union grammar detailed description and examples tutorial This article describes how to use union in mysql to combine into a single result union Syntax select field1, field2 ... Union [all | distinct] select field1, field2 ... See below a paragraph Query three tables Ordinary methods select brand from car; select brand from c ...

When querying data, we often need to specify a few rows of data to be returned. As now there is a B/s architecture application, each page may display only 30 records. In order to improve the efficiency of the display, the database is generally required to return only 30 records at a time. When the user presses the next page, return 30 records from the database, and so on. This can shorten the time that the data is displayed. This is very effective when the base table for the query is larger. You can use the Limit keyword to implement this requirement at this time. The limit clause can be used to force a SELECT query statement to return ...

With the proliferation of data volume, Mysql+memcache has not met the needs of large-scale Internet applications, many organizations have chosen Redis as its architectural complement, however, redis the use of the threshold is not low, such as not supporting SQL, here for everyone to share the Redis use of the full raiders. Redis, one of the most closely watched NoSQL databases, has been used by many well-known internet companies, such as Sina Weibo, Pinterest and Viacom. However, being born with no support for SQL makes him look difficult ...

Method 1 delete yourtable where [id] not in (select max ([id]) from yourtable group by (name + value) b on a.id = b.id where b.id ...

Over the past few years, we have been devoted to refactoring Digg's architecture, which we now call "Digg V4." In this article we will give you an overview of Digg's systems and technologies. Find the secret of the Digg engine. First of all, let's take a look at the services that Digg provides to mass users: A social news site is a customizable social news advertising platform. API services Blog and documentation sites People use browsers or other applications to ...

MongoDB in the latest version of the 2.4 User Rights Management made a new adjustment, the permissions are refined, enhanced security, more and more like the permissions of MySQL management. 2.4 Before the version of User Management 1, the creation of a database management user 1.1, access to the WEIW database: >use weiw; 1.2, add users (Read and write permissions, Readonly-->false): >db.adduser ("java", "Ja ...)

Fish refused to swim March 2008, Zhejiang Shaoxing. Through the cold winter of the southern vitality, the Internet in the spring of the atmosphere in this ancient city appears particularly strong. Dong Qin-Feng lying in the hospital dozen intravenous drip, has been a few years not sick body in the spring and winter of the turn can not resist the attack of cold virus. Lying in the drip room, he sighed, finally have a reason to let him temporarily leave the network, leaving the busy computer table. Looking out of the window on the branches of the bud, he suddenly felt very relieved. In a few days, is the laggards forum opened seven anniversary, every year this time the laggards forum will organize all over the webmaster into ...