MySQL

To understand the MySQL implementation process, it is true that the search keyword is replaced by "MySQL statement execution plan", after all, "plan" the word more standard-------------------------------------------------http://blog.csdn.net/u0140448

Select_type:select type1), simple (Do not use union or sub-query, etc.)2), PRIMARY: Outermost Select3), DERIVED: Select of Derived table (subquery FROM clause)4), the second or subsequent SELECT statement in a union:union5), UNION result:union

Show status like ' handler_read% ';Handler_read_key represents the number of times a row is indexed, and a low value indicates that the index is not frequently used, and that increasing the index is not a good performance

Using the SUM function, plus the group by Person ID, can be implemented:SELECT sum (PZ+CPJS+BZ+GC+SB+TG+MJ+CL+CCLW+GJ+ZL+CBZZ) as Count, SUM (PZ) as Pz,sum (Cpjs) as Cpjs,sum (BZ) as Bz,sum (GC) A S Gc,sum (SB) as Sb,sum (TG) as Tg,sum (MJ) as

One: Check the installation path:1, nginx Installation path:Ps-ef | grep nginxPress ENTER to appear as a slice:After the master process is the Nginx directory.2. mysql Installation path:Ps-ef|grep MySQL to produce results Root 17659 1 0 2011

Add columns:Alter Tabletable_nameAddNamevarchar( -);Alter Tabletable_nameAddNamevarchar( -) after ID;Alter Tabletable_nameAddNamevarchar( -) First; Modify the column name:Alter TableTABLE_NAME Change name Namevarchar(Ten); #change可改名字与字段类型mysql>

Lab Environment: CentOS7[email protected]~ localhost] #yum-y install Mariadb-server[[Email protected]~localhost] #mysql_secure_installation #数据库安全加固note:running All PARTS of this SCRIPT are RECOMMENDED for all MariaDB SERVERS in PRODUCTION use!

1. Background* multi-table joint query is a way to record different tables together* The Federated (join) plan in the SQL standard is roughly the same as the connection, outer connection, and full connection. The outer connection is divided into

First of all, it is necessary to execute the delimiter, the proposed use//, that is, before the beginning of the stored procedure definition delimiter//, after the end Plus//, and finally add delimiter; The specific reason @ Reference Article 1

1. Background* curd operations are typically done using the Structured Query Language (structured Query language,sql) in a relational database system* Curd defines the basic atomic operations used to process the data* Curd represents creation

[Email protected] ~]# yum-y install gcc gcc-c++ autoconf automake zlib* fiex* libxml* ncurses-devel libmcrypt* libtool- ltdl-devel* make CMake libaio libaio-devel autoconf BZR Bison libtool[[Email protected] ~] #groupadd MySQL[[Email protected] ~]

1: Go to cmd, stop MySQL service: Net stop MySQL (enter service---->mysql-----> Stop) to MySQL installation path to start MySQL, Use Mysqld-nt.exe boot in bin directory, 2: Execute: Mysqld-nt--skip-grant-tables (window will stop) 3: Then open

What is an index? A database object in the schema.Used in a database to speed up queries against a table.Reduce disk I/O by using quick access methods to determine location dataSeparate from table, but cannot exist independently, must belong to a

Several steps to analyze the problem:　　1. Turn on the slow query log.This step is to record the SQL of the slow query, to prepare for the next step, the relevant knowledge points of this step are as follows:1. Show variables like '%slow_query_log% ';

MySQL compilation installation 1. Create MySQL Account[[email protected] ~]# useradd-s/sbin/nologin-m MySQL2. Get the installation packagehttp://mirrors.sohu.com/mysql/Choose the version you want (note the difference between the binary package

1. Background* in MySQL 5.7.8, MySQL supports the native JSON data type defined by RFC 7159, which supports effective access to data in JSON (JavaScript object tagging) documents.* MySQL automatically validates DML JSON data. An invalid DML JSON

1, Stop the service:Service Mysqld Stop2, modify MY.CNF:1 vim/etc/my.cnf23# Add 4 skip-grant-tables3. Start the service:Service mysqld Start4. Login and Change Password:1 # Login Database 2 MySQL 3 # Change Password 4 Update Mysql.user set Password=

MySQL parameter optimizationInnodb_buffer_pool_size:Write Innodb_log_bufferbuffer write full or transaction commit, refresh data large transaction frequently, increase innodb_log_buffer_size size, for a separate MySQL database server recommended set

MySQL functions-string functions, mysql function strings CHAR_LENGTH (str) returns the number of characters in str LENGTH (str) returns the LENGTH of str bytes. CONCAT (str1, str2....) returns the concatenation of str1, str2..... If there is a

The group_concat () function data used in MySQL is intercepted (with the default length limit). Exercise caution !, Mysqlgroup_concat Recently encountered a problem at work: Some of our system's logic processing is implemented by the storage process.