MySQL

MYSQL's MERGE storage engine MYSQL engine is not generally many. This time we talk about MERGE, which has many special features: the www.2cto.com MERGE engine type allows you to MERGE many tables with the same structure into one table. Then, you can

The use of pager commands in mysql is in mysql. in linux, the use of pager commands will greatly improve work efficiency. The following describes several examples: 1. First, let's take a look at the basic usage of www.2cto.com mysql> pager less

Mysql exercise Alter usage summary alert usage Summary: alter database syntax alter database is used to change the global features of a DATABASE. These features are stored in the db. opt file in the database directory. To use alter database, you

Skip-grant-tables: a very useful mysql startup parameter -- skip-grant-tables. As the name impliesGrant-tables is not enabled for mysql. What is the purpose? Of course, it is useful when you forget the administrator password. Www.2cto.com Operation

MySQL queries do not use index summary. We all know that adding an index is an effective way to increase the query speed. However, in many cases, even if an index is added, the query still does not use an index, which seriously affects the

In MySql, the original table showing the number of consecutive occurrences of the same value in a column is as follows: www.2cto.com 100101102100100103104102102105106101101 output: www.2cto.com 100 1101 2102 3100 4100 4103 5104 6102 7102 10 SQL: SET

It is important to specify the encoding and sorting rules when creating a database in MYSQL. Many developers use the default encoding, but from my experience, coding databases can avoid garbled characters caused by import and export. Www.2cto.com

MySQL query optimization: Connection query sorting limit (join, order by, limit statements) does not know if anyone has encountered such a disgusting problem: two tables are connected for query and limit, and the SQL efficiency is very high,However,

Mysql case... the usage of the when statement is generally case... when is used in select statements, but 1 can be used in other clauses to perform custom sorting in order by clause www.2cto.com SQL code show create table 20130225t1; create table '20

Due to various reasons, I recently think that Ubuntu and Windows 7 systems are very uncomfortable, so I am bored with formatting the hard disk and re-installing a new Ubuntu single system. It seems that I haven't been in touch with a single-system

Mysql update statement value nested select Java code update a set col = (select col from a where id = '5') where id> 5 and id 5 and id

Mysql max_allowed_packet queries and modifies the size of data packets received by the server according to the configuration file. Sometimes large inserts and updates are limited by the max_allowed_packet parameter, resulting in failure. View the

Mysql index learning Notes 1. advantages and disadvantages of indexes: speeding up the query speed and downgrading: it affects the rate of table deletion and modification operations and increases the file size (the index file may be larger than the

The value status (Stored Procedure + scheduled task) of the regularly updated table field column now has two more tables, tcm and doc; db_count: id count1 2202 3003 2204 2225 240db_date: id t_date count 1 17:04:07 2202 15:04:07 2243 11:04:07 2254 17:

Mysql re-installation steps: ① enter the control panel, in the add and delete programs, delete mysql. ② Enter regedit in the Start-run column to enter the registry, press F3 to search for mysql items, and delete the mysql items. ③ Search for

Mysql Chinese garbled characters and export as SQL statements and Excel problems solvedI wrote a crawler based on Heritrix over the past few days and used mysql to import and export data. When I encountered some garbled code problems, it was hard to

MySQL master-slave replication several important startup options (1) log-slave-updateslog-slave-updates this parameter is used to configure whether to write updates from the server to binary logs, this option is disabled by default. However, if the

In Mysql, varchar and text note Varchar occupy two bytes for each English (ASCII) character, and one Chinese character only occupies two bytes for char and one English (ASCII) character, the type of a Chinese character that occupies 2 bytes of

MySQL multi-column partitioning a table created for an instance of MySQL5.5 COLUMNS partition: Java code drop TABLE if exists partition_test; CREATE table 'partition _ test' ('t _ id' int (11) not null AUTO_INCREMENT, 'test _ date' datetime not null,

In Mysql, the field null has two different meanings: 1. The field value is null; 2. The field value is a null string to remove the null value: SQL code create table B select column 1, column 2, IFNULL (column 3, 'I am null') as column 3, IFNULL