key index

Source: Drill down into the MySQL kernel1 Problem DescriptionHow does a SQL work in a database? I believe a lot of people will be interested in this problem. Of course, to fully describe a SQL in the database life cycle, this is a very big problem,

1. What is a database index?A: An index is a data structure that sorts the values of one or more columns in a database. Emphasis: A data structure that sorts the values of a column.Use indexes to quickly access records in a database2. What is the

When talking about database performance optimizations, it is common to refer to "indexes", but many people do not really understand the index, nor do they know why the index can speed up the retrieval so that the index is not applied well in

A: whyBecause the data is stored in a database table, the index is created on a database table object, consisting of keys generated by one field or multiple fields in the table, stored in a data structure (b-tree or hash table) that can quickly and

1. In MySQL, there are four main types of indexes:Primary key index (PRIMARY key)Unique index (unique)Regular Indexes (index)Full-text index (fulltext)2. Primary KEY indexA primary key index is the most common type of index in a relational database,

Common query indexes of mongoDB (III)1. _ id index is the default index created by the vast majority of sets. For each inserted data, MongoDB automatically generates a unique _ id field. > Db. jerome_2.collection.insert ({x: 2}) WriteResult

Lock Introduction InnoDB supports row-level locks and table-level locks. The default value is Row-level locks, which include table-level locks, row-level locks, and page locks. Introduction to deadlocks Lock conflicts and deadlocks are not a

Hash Index Because of the particularity of the hash index structure, the retrieval efficiency is very high, and the index retrieval can be located at a time, unlike B-tree indexes that need to go from the root node to the branch node, the hash index

ED/EP Series 4-memory labeling command, edep1. Inventory transactionThrough the deposit transaction, the cardholder can transfer the funds in the corresponding account of the bank into the electronic passbook or e-wallet. Features:1) -- must be

Test Case Description The test case is in the B2C field. A product order information table is used to store the purchased items. However, some other fields are removed for testing and the data items in the table are not described in detail, field

Here we want to summarize the previous index learning notes: First, understand why the index increases the speed. When DB executes an SQL statement, the default method is to scan the entire table based on the search conditions, and add the matching

Mysql index and Optimization: 1. what is the index? 2. index type and syntax. 3. full-text index description. 1. what is the index? 1. take the book directory as an example. view the directory, then find the corresponding content. Therefore, the

Database index You can use indexes to quickly access specific information in database tables. An index is a structure that sorts the values of one or more columns in a database table, for example, the last name (lname) column of the employee table.

This article mainly introduces the index optimization distinct statement and the multi-field operation method of distinct in MySQL. the de-duplication function of distinct statements is the basic knowledge in MySQL beginners, for more information,

How to create mysql indexes and the advantages and disadvantages of indexes bitsCN.com Mysql Tutorial: how to create mysql indexes and the advantages and disadvantages of indexes: 1. index is a data structure that helps MySQL efficiently obtain

 Field property settingsNot NULL is not emptyAuto_increment sets the value of the Int type field to "self-grow", meaning that its value does not need to be "written" and is automatically obtained and incrementedNote: This property must be used

Mysql index typeIn MySQL, there are four types of indexes: B-Tree index, Hash index, fulltext indexes and RTree indexes 1. B-Tree indexes are the most frequently used index types in MySQL databases, all other storage engines except the Archive

About innodb locks (record, gap, Next-Key lock) and innodbnext-key Record lock locks a single index record. Record lock always locks the index instead of the record itself, even if the table does not have any indexes, then innodb will create a

Create and delete indexes The creation of the primer can be done in the CREATE TABLE statement, or you can add indexes to the table separately with the CREATE INDEX or ALTER TABLE. The deletion index can be implemented using ALTER TABLE or DROP

MySQL optimization in three directions ① optimize MySQL Server Core (this optimization is usually done by operations personnel). ② tuning MySQL configuration parameters (my.cnf) This optimization requires a stress test to adjust the parameters. ③ to