count from

Like most relational databases, log files are an important part of the MySQL database. MySQL has several different log files, usually including error log files, binary logs, generic logs, slow query logs, and so on. These logs can help us locate

In the help of imp: SHOW just list file contents (N). The default value is N. The Code is as follows: Copy code In the help of imp: SHOW just list file contents (N). The default value is N.The following experiment explains

Oracle SQL Performance 1. ORACLE optimizer:. RULE (based on Rules) B. COST (COST-based) c. CHOOSE (optional) sets the default optimizer. various declarations of the OPTIMIZER_MODE parameter in the ora file, such as RULE, COST, CHOOSE, ALL_ROWS,

The mysql group obtains the first few records (ranking) in each group and the groupby and orderby research bitsCN.com -- obtains the data of the row where the maximum (small) value is located by grouping by a certain field /* The data is as

Let me see how to write this mysql statement! Test Name add num A wefsv 3 B asdf 4 B wers 9 B w1rs 10 As asdf 11 As wers 12 As w3rs 13 For example, in the preceding table, select * from test ...... To select the following result (the

When mysql is used with a massive data volume of tens of millions, we will mostly consider Table sharding queries and database sharding queries. Next we will introduce the optimization of table sharding queries. When mysql is used with a massive

20 basic optimizations and references for MySQL and 20 for MySQL Mysql has a wide range of performance optimizations:Index optimization, query optimization, query cache, server setting optimization, operating system and hardware optimization,

Steps for viewing and modifying the maximum number of connections in ORACLE Step 1: On the cmd command line, enter sqlplus Step 2: Enter the user name and password as prompted 1. view the processes and sessions Parameters SQL> show parameter

The following articles mainly describe how to query and set globalquery_cache_size for MySQL cache. We all know that when the access volume increases, the pressure on the MySQL database will increase! What if we reduce the pressure on it? Cache

Mysql database groups are divided into three methods. Temporary tables are used for group by, compact (Tight) index scanning, and group by and Loose index scanning, but I often use 1. Use Loose index scanning to implement GROUP What is loose index

0. Oracle test data preparation:[Oracle @ db1 ~] $ Sqlplus system/000000SQL * Plus: Release 11.2.0.3.0 Production on Tue Mar 25 10:26:06 2014Copyright (c) 1982,201 1, Oracle. All rights reserved.Connected:Oracle Database 11g Enterprise Edition

Basic tutorial on querying the cache mechanism of MySQL, The MySQL cache mechanism simply caches the SQL text and query results. If the same SQL statement is run, the server directly obtains the results from the cache without parsing and executing

Restore accidentally deleted oracle data files Recovery Method for accidental deletion of oracle data files on the Linux platform simulates misoperations: the database is running normally and data files are directly rm. -- 1. test Environment: $ cat/

The MySQL query cache mechanism is one of the important mechanisms in the MySQL database. The following provides an in-depth analysis of the MySQL query cache mechanism for your reference. The MySQL cache mechanism simply caches the SQL text and

I. Introduction of row migration and row link in actual work we often encounter some problems with low Oracle database performance. Of course, there are many reasons that cause low Oracle database performance, we can use some correct design and

MySQL table sharding optimization bitsCN.com many of our projects are unequal. This article briefly analyzes how to optimize it. The table sharding logic here is based on the number of user_name groups in the t_group table. In this case, the index

In the help of imp: SHOWjustlistfilecontents (N), the default value is N. In the help of imp: SHOW just list file contents (N). The default value is N. In the help of imp: SHOW just list file contents (N). The default value is N. The

ID, name (person name), Class (class), Fen (score) 1 JJ 1 88 2 J1 1 90 3 J2 2 70 Select the first two scores for each class and display the class, name, score ???????? Create Table # T (ID int, name varchar (20), Class varchar (10), Fen

Oracle common SQL syntax set Table:Select * from cat;Select * From tab;Select table_name from user_tables;View:Select text from user_views where view_name = upper ('& view_name ');Index:Select index_name, table_owner, table_name, tablespace_name,

1. During the interview, I encountered a problem. I wrote a table with two fields, ID and name, to query all the data with duplicate names. The column is: Select * from Xi A where (A. username) in (select username from Xi Group by username having