MySQL

SELECT Group_concat (md.data1) from DATA md,contacts cc WHERE md.conskey=cc.id and md.mimetype_id= 5 and md.user_id=17:Use the function: Group_concat (), to implement an ID corresponding to multiple names, originally multiple rows of data, the name

Mysql:1.left ()//left () functionLeft (A, A, b) intercept A,2.mid ()//mid () function Parameters Describe column_name Necessary. The field to extract the characters from. Start Necessary.

Linux version: CentOS7 64-bitPrerequisites Download: Http://dev.mysql.com/downloads/mysql/5.6.html#downloadsDownload version: I choose here 5.6.33, General edition, Linux under 64-bitYou can also directly copy the 64-bit, download by command: wget

After installing MySQL in CentOS, the default is no root password, the default is carriage return,Then to facilitate the need to change the password.No password for MySQL plus password: mysql-uroot-p Enter prompt for password, empty enter update

One, add users and Groups1. Add a MySQL user group# Groupadd MySQL2. Add MySQL User# Useradd- g mysql-s/bin/nologin mysql-mSecond, check whether MySQL is installed in the system, if the installation needs to uninstall# Rpm-qa | grep mysqlmysql-libs-

Due to the work of the regular feedback is the Excel format of the file, in order to facilitate the preservation and collation found MySQL for Excel this tool. This tool is very useful.First,

3 different ways to connect: INNER Join (inner connection, or equivalent connection) : Gets a record of the field matching relationship in two tables. left join (right-hand connection): gets all records for the left table, even if the

The MySQL 1366 error is roughly described below SQL error:1366:incorrect String value: ' Xe8xafxa6xe7xbbx86 ... ' for column ' address ' at row 1 Workaround: Check the database the character set of this field is the same as the

MySQL Master-slave replicationMySQL ReplicationMySQL replication supports one-way, asynchronous replication. Writes updates to the binary log file through a primary server and maintains an index of the file to track the log loop. These logs can

One, why redundant dataInternet data volume of business scenarios, often the database needs to be horizontal segmentation to reduce the amount of single-Library data.The horizontal cutting branch has a patition key, the query with Patition key can

Loop structure whileCreate procedurename ()begin whileconditional do SQL statementsEnd while; End$Create procedureaa6 ()begin Declare Number int default 0; while Number 5 DoSelect Number; Set Number = Number + 1; End while;

Mysql-versionMysqladmin Ver 8.42 distrib 5.7.12, for Win64 on x86_64Use Insert to create a new user, error:INSERT INTO user(host,user,authentication_string)VALUES (' localhost ', ' Hupi ', PASSWORD (' 123456 '));ERROR 1364 (HY000): Field '

1. Open configuration File modificationShell>vi/etc/my.cnfAdd below [mysqld]Skip-grant-tablesThen press the ESC key to enter: Wq carriage return2. Restart MySQL after savingShell>service mysqld Restart3. So you can enter without a password, and then

The content of this article is still to discuss the MySQL field type is timestamp timestamp problem, after encountering the problem before, today the tester gave me a bug, is to submit a meeting form on the front page, select a meeting time (2059

Overwrite index: MySQL can use the index to return the fields in the select list without having to read the data file again according to the index. The index of all data required to satisfy the query is called the Overwrite index (covering index) if

Turn http://www.jb51.net/article/48625.htmWeb page today to submit content to the database, found that the error, has not been submitted, the number of the next reason to find the data can not be written in! The first reaction, restart the MySQL

View Index mysql> Show index from tblname;mysql> show keys from tblname; The name of the table sheet. Non_unique 0 If the index cannot include a repeating word. 1 if it is possible. · The name of the Key_name index. Seq_in_index the column sequence

MySQL functions-Date and Time Functions, mysql function date CURDATE (), CURRENT_DATE () returns the current date 'yyyy-MM-DD' CURTIME (), CURRENT_TIME () returns the current time 'hh: MM: ss' CURRENT_TIMESTAMP () LOCALTIME () NOW () Both SYSDATE (

Locks RocksDB and locks rocksdb. As an open-source storage engine, RocksDB supports ACID features of transactions. To support I (Isolation) in ACID, concurrency control is indispensable. This article mainly discusses the implementation of RocksDB

Mysql optimization 1 (20170703), mysql optimization 20170703 1. Table Structure Create table 'room _ break_history_tmp_test '('Id' INT (11) not null AUTO_INCREMENT,'Break _ type' INT (11) default null,'App _ id' INT (11) default null,'Room _ id' INT