MySQL

Ifnull (expr1, expr2), if expr1 is not null, ifnull () returns expr1, otherwise it returns expr2. Ifnull () returns a number or string value, depending on the context in which it is used. Mysql> select ifnull (1/0);-> 1 mysql> select ifnull ();-> 0

We always hope to avoid full table scanning by the database engine when doing some queries, because the full table scan takes a long time, and most of the scans do not make sense to the client. Which of the following methods can be used in MySQL to

I will continue to solve the index problem of MySQL this time. There are still many principles that can be summarized as follows: 1. For composite indexes, if one of the leftmost query conditions is used,For example, if an index (a, B) exists,

The command line is used as follows: Mysqldump-u use the primary name-P password-D database name Table Name> Script Name;     Export the entire database structure and dataMysqldump-H localhost-uroot-p123456 database> dump. SQL   Export the structure

$ Mysql-uroot Error 1040 (00000): Too connector connections The above error is probably encountered by many people. aurimas mikalauskas has mentioned a solution in the MySQL performance blog (with caution in the production environment ): $

Overview of log file types:1.The error log records the problems that occur when you start, run, or stop mysqld.My. ini configuration information:# Enter a name for the error log file. Otherwise a default name will be used.# Log-error =

  (AH) recently, due to work needs, I finally started to play with Linux. Today I have compiled and installed MySQL for a day and recorded it. Forget it !!   (Card) installation environment: vmware5 (Bridge Mode) + RedHat e as 4 + have installed

1. Install apahce,PHP,MySQL,And PHP connection to MySQL library components.Yum-y install httpd PHP MySQL mysql-server PHP-MySQL 2. Configure the startup Service /Sbin/chkconfig httpd on[SettingsApacheServer httpd service startup] /Sbin/chkconfig --

#!/bin/sh##install mysql database#echo -e "/n/n"while echo -en "/nAre you sure install mysql database now (yes/no)?";read qrdo if [ "$qr" = "yes" ]; then break elif [ "$qr" = "no" ]; then exit 1 fidonewhile echo -en "/nPlease input install

MySQL replication is a simple and common database load balancing method. Here we record the specific process of Environment setup: Environment: Two Ubuntu instances, one master instance and one slave instance. MASTER: ubuntub (192.168.1.101) SLAVE:

It is very important to specify the encoding when creating a MySQL database. Many developers use the default encoding, but from my experience, coding databases can avoid garbled characters caused by import and export.The standard we follow is that

Postfix + sasl2 installation Note: You have been installing Postfix + sasl2 for nearly a week and have passed MySQL authentication until the initial success in the afternoon. The steps and experience are summarized as follows: Determine the version

The data table of the experiment is defined as follows: mysql> DESC tbl_name; + ------- + -------------- + ------ + ----- + --------- + ------- + | FIELD | type | null | key | default | extra | + ------- + -------------- + ------ + ----- + ---------

Partitioned table created Create Table 'employees '('Id' int (11) not null,'Fname' varchar (30) default null,'Lname' varchar (30) default null,'Hired' date not null default '2017-01-01 ','Separated 'date not null default '2017-12-31 ','Job _ Code'

First, go to the Linux system. The database is MySQL, which contains database: bugs. Create a directory in/root: mkdir dbbak, and then create a directory in dbbak: mkdir bugsbak VI mysql_bugs.sh/* Create a mysql_bugs.sh file */ Enter two rows of

  The configuration in Tomcat, which was previously used, can be found: factory org. Apache. commons. DBCP. basicperformancefactory driverclassname org. gjt. Mm. MySQL. Driver The autoreconnect = true argument to

We know that MySQL 5.1 supports horizontal partitioning. Let's try to optimize the query on a partitioned table.In general, the optimization principle is the same as the optimization for individual tables, ensuring that the number of scans on the

Show tables or show tables from database_name;Explanation: displays the names of all tables in the current database. Show databases;Explanation: displays the names of all databases in MySQL. Show processlist;Explanation: displays all processes

Description: There is a member table, there is a birthday field, the value is 'yyyy-MM-DD 'format, now to query the birthday of a member within a period of time, for example, from '06-03' to '07-08 ', all the Members who celebrate their birthdays in

Enter Password :******Welcome to the MySQL monitor. commands end with; or \ G.Your MySQL connection ID is 57Server version: 6.0.4-alpha-Community-log MySQL Community Server (GPL) Type 'help; 'or' \ H' for help. Type '\ C' to clear the buffer. Mysql>