mysql query order by

Index | conditions Original post address: http://community.csdn.net/expert/FAQ/FAQ_Manage.asp?id=0Topicid=3390663 Environment: SQL Server2000 +SP4 Problem: Select DateDiff (Day, ' 20040910 ', ' 20040920 ')--this sentence can be executed --and the following sentence cannot be executed (sometimes it can be executed) --sub_para is varchar (8) and the error message is: A syntax error occurred while converting from string to DateTime. SELECT * FROM T_sub where item_local_code= ' 03004 ' and DateDi

challenges, especially in the big promotion, the order database has become a system bottleneck.There are usually two workarounds:Scale up, which upgrades the physical machine where the Oracle database is located, improves memory/storage/io performance, but this upgrade is expensive and can only meet short-term needs.Scale out, split the order library into multiple libraries, dispersed across multiple machi

|+ ---- + -------------- + -------- + ------- 10 use the DISTINCT keyword to remove duplicate rows in the result For example: Original table: mysql> select * from library; + ---- + --------------- + -------- + ------- + | Id | name | author | price | + ---- + --------------- + -------- + ------- + | 1 | java example Daquan | Zhang Fan | 99 | | 2 | mySQL | Pan Kaihua | 50 | | 3 | SQLserver2005 | Liu Zhiyong

(2) Default NULL,' C3 ' varchar default NULL,' C4 ' datetime default NULL,PRIMARY KEY (' C1 ')) Engine=myisam DEFAULT Charset=utf8Sky@localhost:example 01:48:32> Show CREATE TABLE BG1. Row ***************************Table:bCreate table:create Table ' B ' (' C1 ' int (one) not NULL default ' 0′,' C2 ' char (2) Default NULL,' C3 ' varchar default NULL,PRIMARY KEY (' C1 '),KEY ' B_c2_ind ' (' C2 ')) Engine=myisam DEFAULT Charset=utf8 1, the use of ordered index sorting, in fact, when we

Detailed usage of count (), group by, and order by in mysql, and detailed usage of mysql I encountered a problem when I was doing IM recently and used these three keywords at the same time. This is to query the offline message details of a person. The details returned by the server to the client include three items. Th

displayed. do not use the gb2312 or GBK character sets. If you are worried about query sorting and other issues, you can use the Binary Attribute constraints, such: Create Table my_table (name varchar (20) binary not null default'') type = MyISAM default charset Latin1; Since then, the complete example of using the utf8 character set has ended.III,Old Data Upgrade Method(1)Export Database:Mysqldump-uroot-p123456 -- default-character-set =

Tags: nbsp color cal pos Col cores core round. ClassLeftist query SELECT * from a LEFT join B on a.id=b.id; Right Union query SELECT * from a RIGHT join B on a.id=b.id; inline query Select A.name,b.class from A, b where c.id=b.id; ORDER BY Select *from a order by Desc#desc;

Optimization Methods for mysql nested queries and table queries: bitsCN.com poor optimization of nested queries As mentioned above, join table queries are more effective than nested queries without special considerations. Although the two queries share the same meaning, even though your plan is to tell the server what to do and then let it decide how to do it, sometimes you have to tell it how to change it. Otherwise, the optimizer may be stupid. I ha

these queries This is a useful log. It has little impact on performance (assuming all queries are fast), and emphasizes those queries that need the most attention (missing indexes or indexes are not optimally applied) # time:070927 8:08:52 # User@host:root[root] @ [192.168.0.20] # query_time:372 lock_time:136 rows_sent:152 rows_examined:263630 Select ID, name from manager where ID in (66,10135); This is a slow query log in a, 372 seconds, locked 136

Label:Transferred from: http://www.cnblogs.com/likwo/archive/2010/04/16/1713282.htmlQuery Day: SELECT * FROM table where to_days (column_time) = To_days (now ());SELECT * FROM table where date (column_time) = Curdate (); Query one week: SELECT * FROM table where Date_sub (Curdate (), INTERVAL 7 day) Query one months: SELECT * FROM table where Date_sub (Curdate (), INTERVAL 1 MONTH)

Most of the time, we created an index in MySQL, but some queries are still slow, and no index is used at all! In general, some fields may not have been indexed, or the order of the fields in the composite index does not match the order of the fields in the query statement.Look at the following example:Suppose there is

Mysql random query record set and mysql query record Sometimes, you need to randomly query several record sets from the database. After searching online, several blog posts are repeated ..... I don't know who copied them. Apart from introducing a method that I think of mysel

file (or, in some cases, switch to a new log) by refreshing the log.When you execute a FLUSH logs statement or perform mysqladmin flush-logs or mysqladmin refresh, the log is aged.In the case of MySQL replication, more log files will be maintained from the replication server, known as the replacement log.2. General Query LogThe common query log can be stored in

Tags: row col query database data SQL DB request field commentSELECT * from information_schema.columns where table_schema = ' db ' #表所在数据库 and table_name = ' tablename '; #你要查的表 In addition to the above method can also add field query Log in to the database using Mysql-uyourroot-pyourpassword Use the database again; You can include the comment information in the

The following transfers are from:http://www.tech-q.cn/archiver/tid-11673.htmlMost of the time, we created an index in MySQL, but some queries are still slow, and no index is used at all! In general, some fields may not have been indexed, or the order of the fields in the composite index does not match the order of the fields in the

Rows_sent: 1 Rows_examined: 1260544 SET timestamp = 1281764236; Select count (*) as cou from ad_visit_history where ad_code in (select ad_code from ad_list where id = 41) order by id desc; As you can see, it is to record the execution of SQL statements, including the execution time and lock time. Therefore, there are many analysis tools to check your personal situation, here we will only talk about how to use mysqldumpslow, a

MySQL order by performance optimization example This article mainly introduces the MySQL order by performance optimization method example. This article explains the principle of order by in MySQL and the three methods to optimize

The most common method to satisfy the group by clause is to scan the entire table and create a new temporary table. All rows in each group in the table should be continuous, then use the temporary table to locate the group and apply the accumulate function (if any ). In some cases, MySQL can do better by accessing indexes instead of creating temporary tables. The most important prerequisite for using an index for group by is that all group by colum

than one return statement, there are multiple exit methods for the function; Instance:mysql> delimiter //mysql> create function doreturn() -> returns int -> begin -> select gender into @a from students where sid = 1; -> if @a=1 then return 1; -> elseif @a=0 then return 0; -> else return 999; -> end if; -> end//Query OK, 0 rows affected (0.00 sec)

Author:flymorn Source: Easy to floatcategories:php Programming Posttime:2011-1-14 15:35:07Text: Recently, due to the need to study the MySQL random extraction implementation method. For example, to randomly extract a record from the TableName table, the general notation is: SELECT * from Content ORDER by RAND () LIMIT 1."Floating Easy note: 30,000 records of the