MySQL

I. OverviewOn the principle of mycat on the web there are many, here no longer detailed, for me, mycat the main functions are as follows:1.Mysql master-Slave read/write separation2.Mysql Large Table Shard3. Read-write separation and sharding of

Date and time data types Date 3 bytes, dates, format: 2014-09-18 time 3 bytes, duration, format: 08:42:30datetime 8 bytes, date time, format:2014-09-18 08:42:30timestamp 4 bytes, automatic storage record modified time year 1 bytes, yearsNumeric data

Knowledge Background:MySQL the default value of the maximum number of connections is 100, for a large number of concurrent connections of the database, when the connection request is greater than the default number of connections, there will be no

Some of the more complex business relationships that are resolved by subqueries. Doha is better than a recycling facility.For example, the following sentence selects and where in statements use subqueries. Because the parent query is in SELECT, the

Using indexes for sortingKEY A_b_c (a,b,c)Order by can use the index leftmost prefix-orderby a-order by a,b-order by A,C-order by a desc,b desc,c descIf where the leftmost prefix of the index is defined as a constant, the order by can use the

What's the only thing?1. All values of the indexed column (field) can only occur once, i.e. must be unique--------------------------------------------------------------------------------The difference between a primary key index and a unique index1.

MySQL Chinese garbled processing Locate the My.ini file (default in the C:\ProgramData\MySQL\MySQL Server 5.7 folder); In the My.ini:Search to [client], modify or add Default-character-set=utf8;Search to [mysqld], modify or add

I've seen a lot of information.varchar (size) variable-length character value saves space and queries are inefficientchar (size) fixed-length character value, wasted space, high query efficiencyBut the actual test of the char (300W) varchar dataFrom

MySQL Data1. Database definition language (data Definition language DDL)A. Alter DATABASEB. Create DatabaseC. Drop databased. ALTER TABLEE. CREATE tableF. drop tableG. Rename tableH. CREATE indexI. DROP Index2. Data manipulation Language (DML)A.

Today, a stored procedure is executed in the MySQL database, and because the MySQL data connection tool is not installed, it is executed in the black box and then the following problem is encountered:Always said it was my problem with the syntax of

The company has a set of Web systems, the user feedback system some of the page access speed is slow, poor experience, and occasionally an HTTP 502 error.This is a typical server-side IO blocking issue, through the access page of the program logic

The concat () function is used to concatenate strings.Exact query: SELECT * from user where name= "Zhangsan"fuzzy query; select * from user where name is like "%zhang%"In actual use, the condition is passed in as a parameter. So we use the concat ()

Bo Master Original, reproduced please indicate the source:The use of the IF () function in MySQL is similar to the three-mesh expression in Java, and is more useful, with the following syntax:if (EXPR1,EXPR2,EXPR3), if the value of EXPR1 is true,

SortSELECTObj.user_id,obj.score, @rownum: = @rownum + 1 as RowNumFrom(SELECTUSER_ID,ScoreFrom' Sql_rank 'ORDER byScore DESC) as obj,(SELECT @rownum: = 0) RThere are duplicatesSELECTOBJ.USER_ID,Obj.score,CaseWhen @rowtotal = Obj.score Then@rownumWhen

In MySQL 5.7 COUNT () selects a clustered index and makes an internal handler function call to get the total number of tables quicklyExecution plan display: Extra:select tables optimized awayIn previous versions of 5.7, the count () request was

querying the entire contents of a data tableMysql> Show tables, #查看当前数据库下的全部表 +--------------------+| Tables_in_ceshi_ku |+--------------------+| Biao | | Ceshi_biao |+--------------------+2 rows in Set (0.00 sec) mysql> select

1.Packets larger than Max_allowed_packet is not allowedA system parameter for MySQL:max_allowed_packet, whose default value is 1048576(1M),Enquiry:show VARIABLES like '%max_allowed_packet% ';Modify the value of this variable: "max_allowed_packet =

MySQL Event scheduled task flushing slow logs, mysqleventPreface Recently, a log system graylog is used to collect mysql slow query logs for subsequent analysis, monitoring, and alarms. The log has been successfully collected to the graylog during

Mysql storage engine and mysql StorageStorage engine Definition The database storage engine is the underlying software organization of the database. The database management system (DBMS) creates, deletes, modifies, and queries data through the

BugFree background Statistics Bug information, bugfree background bugThe following are the Details table information // statistics of the severity Level BugSELECT severity, count (severity) FROM 'bf _ bugview 'where product_id = 476 group by