index mysql

Note: This article is reproduced from http://www.hollischuang.com/archives/914In computer science, a lock is a synchronization mechanism used to forcibly restrict access to resources when executing multiple threads, which is used to guarantee the

MySQL currently has the following types of indexes: Normal index allows the same indexed content to appear (normal) Unique indexes unique can not appear the same value, can have a null value Primary key index Promary key

1.COUNT ()The optimization of count can be implemented by the following SQL　　Mysql> Select COUNT (gnp=10000 or null) as ' >>> > ' from country;+------+------+| >>> |+------+------+| | |+------+------+1 row in Set (0.00 sec)The value returned by

Databases are the foundation of most web application development. If you are using PHP, then most of the database with MySQL is also an important part of the lamp architecture.PHP looks simple, and a beginner can start writing functions in a few

Write in front: In doing Elk logstash processing MySQL slow query log when the problem: 1, the test database does not have slow log, so there is no log information, resulting in ip:9200/_plugin/head/interface anomalies (suddenly appear log data,

DirectoryPreparatory workOperating EnvironmentConfirm your version of the installationDownload MySQLInstall MySQLPreparing the installation EnvironmentCompiling and installingConfigure MySQLSingle-instance configurationSingle-instance configuration

Previously wrote a blog http://leihuang.org/2015/07/22/concurrence-lock/is how to use optimistic lock to solve concurrency problems, but the project pushed to the line after the error, as follows-08-13 15:12:44 [ERROR]

To add a field: ALTER TABLE ' User_movement_log 'Add column Gatewayid int not null default 0 after ' RegionID ' (which field is added later) To delete a field: ALTER TABLE ' user_movement_log ' drop column Gatewayid To adjust the order of fields:

1. IndexAn index is a table of contents that allows you to quickly locate the query data by looking at the index location in the catalog before finding it. For the index, it is saved in an extra file.2.Index is a data structure in the database that

explain SyntaxEXPLAIN SELECT ... Variant: 1. EXPLAIN EXTENDED SELECT ... "Decompile" The execution plan into a SELECT statement, run show WARNINGS to get the query statement 2 optimized by the MySQL optimizer. EXPLAIN Partitions SELECT ... Explain

1. Index function In addition to the ordered lookups mentioned above, the database uses a variety of fast location techniques to greatly improve the query efficiency. In particular, when the amount of data is very large and the query involves more

To add a field:ALTER TABLE ' User_movement_log 'Add column Gatewayid int not null default 0 after ' RegionID ' (which field is added later)To delete a field:ALTER TABLE ' user_movement_log ' drop column GatewayidTo adjust the order of fields:ALTER

I. What is an index?Indexes are used to quickly look for records with specific values, and all MySQL indexes are saved as B-trees. If there is no index, MySQL must start scanning all records of the entire table from the first record until it finds a

explain SyntaxEXPLAIN SELECT ... Variant:12. EXPLAIN Partitions SELECT ... Explain for partitioned tablesInformation contained in the execution planIDContains a set of numbers that indicate the order in which a SELECT clause or action table is

Say 工欲善其事, its prerequisite. Today we will briefly introduce the next explain.Content navigation Id Select_type Table Type Possible_keys Key Key_len Ref Rows Extra Environment ready MySQL

MySQL statement optimizationExample 1: Optimization statement SELECT * from ' Tbl_order_buy_eta ' WHERE ' Id_order ' =1843#通过explain分析语句结果如下mysql > explain SELECT * FROM  ' Tbl_order_buy_eta '  where   ' Id_order ' =1843\g*************************** 

I. GrammarExplain For example: Explain select * from T3 where id=3952602;Two. Explain output interpretation+----+-------------+-------+-------+-------------------+---------+---------+-------+------+-------+| ID | Select_type | Table | Type |

The following articles mainly introduce the actual use of MySQLALTER syntax. We all know that the proportion of MySQLALTER syntax in actual application is still very large, so you can have a good idea about the actual use of MySQLALTER syntax. ALTER

SQL alert adds, modifies, and deletes field syntax instances The alter table syntax is as follows: Alter table "table_name" [Change method] The detailed Writing Method of [change method] varies depending on what we want to achieve. In the changes

Experience Sharing: building a social engineering database TIPS Recently, we have been building a social engineering database. There are also many articles on the Internet, but few details are involved. I would like to share some of my experiences