mysql query order by

Slow query of MySQL-delete slow query logs I. environment OS: CentOS release 5.8 (64-bit) DB: MySQL5.5.17 II. operations Run the rm-f command to delete the slow query log. III. problems The slow query log is not automatically generated. (if there is a backup, it is

Compare the buffer query and no buffer query of MySQL in PHP, phpmysql About cache query and unbuffered QueryThe MySQL client has two types of queries:Buffer query:The query results will be received and stored in the client cache,

first statement does not use the index is due to a two-level index problem:InnoDB Level Two index is the current column+ corresponding to the primary key, query with the primary key value to the primary key index to query the corresponding row. In InnoDB, each record in a secondary index contains the primary keyColumns for the row, as well as the columns specified for theSecondary index. InnoDB us

Recently, because of the need to study the MySQL random extraction implementation method. For example, to randomly extract a record from the TableName table, the general wording would be: SELECT * from TableName ORDER by RAND () LIMIT 1. But then I looked up the official MySQL manual, and the hint for rand () probably meant that the rand () function could not be

key2=constant order by Key_part2; * Simultaneous use of ASC and DESC: (Key_part1,key_part2 to establish a federated index) The code is as follows Copy Code SELECT * from T1 ORDER by Key_part1 DESC, Key_part2 ASC; * The index keys used to search for records are not the same as those made by: (Key1,key2 indexed separately) The code is as follows

Tags: cimage order alt dependency span Add table structure trap issuesIn MySQL we often use order by to sort, use the limit to page, when we need to sort after the pagination when we often used a similar wording select * from table name order by sort field LIMT m,n. But this writing hides a deeper use trap. In the case

About buffered queries and no buffer queriesThere are two types of queries for MySQL clients:buffered queries: will receive the results of the query and store them in the client's cache, and the request to obtain row records is only obtained locally.(1) Advantage: You can move the "current row" pointer freely in the result set, which is easy to find because the result is in the presence of the client.(2) Di

MySQL InnoDB b-tree index using TipsHere is the main discussion about the use of InnoDB B-tree index, do not mention the design, just use. The B-tree index primarily acts on the Where and order by clauses. It's all discussed here in the mysql-server-5.1.42 test.CREATE TABLE ' friends ' (' ID ' int () UNSIGNED NOT NULL auto_increment, ' UID ' bigint (a) UNSIGNED n

Personal Original address: http://www.phpthinking.com/archives/433In the database we usually index some of the fields, which can improve the query speed of the data, and improve the performance of the database like order by, the group by before the index needs.First, we need to pay attention.1>mysql only one index can be used for a

Mysql uses indexes to optimize order sorting Original address: http://www.phpthinking.com/archives/433 In the database, we usually perform index operations on some fields, which can improve the data query speed and improve the database performance such as order by and group. Please note that1> only one index can be use

index keys:SELECT * FROM t1 order by key1, key2; 2> order by on the non-consecutive index key:SELECT * FROM t1 WHERE key2 = constant order by key_part2; 3> both ASC and DESC are used:SELECT * FROM t1 order by key_part1 DESC, key_part2 ASC; 4> the index key used for searching records and the

Http://www.codesky.net/article/200903/148361.html The following describes two sorting implementation methods and implementation diagrams through examples: Assume that two tables, table A and Table B, have the following structures: 1. sort by ordered index,In fact, when the order by condition of our query is exactly the same as the index key (or the previous index keys) used in the

This article mainly introduced the MySQL order by performance Optimization Method Example, this article explained in the MySQL the order by principle and the optimized order by three kinds of methods, needs the friend to be possible to refer to under Objective During the w

A bit of a problem occurred today in the process of using the order by, and it was wrong to understand that it was previously understood. See the use of order by on the W3s Web site before, thinking that the selected data is sorted in ascending or descending order of keywords, and as a result of today's attempt to select DataSet data, it is found that the

Php mysql implements login and fuzzy query functions. mysql fuzzy query The software version used in this article is as follows: PHP version 5.5.12; MYSQL version 5.6.17; wampserver for Apache 2.4.9I. PHPMYSQL LoginThere are two files in total:Login. phpAndLogincheck. php;Fo

* from [table] WHERE uid=1 ORDER x, y LIMIT 0, 10;Indexing (Uid,x,y) achieves an order by optimization, which is much better than establishing a (X,Y,UID) index. MySQL ORDER by cannot use an index to optimize the sorting situation* ORDER by for different index keys: (key1,k

Key_part1 DESC, Key_part2 ASC; * The index keys used to search for records are not the same as the order by: SELECT * from T1 WHERE key2=constant order by Key1; * There are many tables connected together, and the fields in the read record are not all from the first very many tables (that is, the connection type of the first table in the result of EXPLAIN analysis is not const). * Different

From: http://www.tech-q.cn/archiver/tid-11673.html Most of the time, we have created an index in MySQL, but some queries are still very slow and no index is used at all!In general, it may be that some fields do not have an index, or the order of the fields in the composite index does not match the order of the fields in the q