Database Administrator

This is the first article about SQL optimization. Here, I mainly express my point of view that if an index does not exist, it should be eliminated, leaving it in the way. During the period from 15:39:01 to 15:55:00, we found two problems in a

1. simple aggregation tools 1. count Count is the simplest aggregation tool used to return the number of documents in the collection. 2. distinct The semantics of distinct is the same as that of other databases. It is used to find all the

/* Author: Jiangong SUN */ I 've encountered a problem when I do a SQL bulk copy from a table in staging to the same table in production. Should t for a same column has different types. So when I synchronize the data, I have the following error:

Tracking the DBCA database creation log to facilitate exception resolution, that is, when you are running the dbca database creation, you can look at it when you are bored. Method 1: (view the log location provided by oracle) Dbca in 10g and

Today, we found a bug in the project, that is, about field sorting. I wanted to get the result as follows: However, the result is as follows: Put the A1 fan to the last one: It is determined that it is not a plug-in problem, it must be an SQL

In order to install the cluster, the study took 2 days to complete, so the study experience was recorded for your reference, to avoid repeated detours, the installation is divided into the following stages:Environment Description: CentOs6.5 +

The text format is as follows: [File path] [Configuration information] Write For more information, see the source. This article is from the swordsmanship. If you have any questions, please leave a message. 1. First, configure linux to access the

There are usually many data types in the database and different classification methods. For example, the most common numeric, numeric, and datetime types are also uncommon Boolean, enumeration, and set types. To support a specific data type (such as

Problem description: Recently, I am working for a school. NET website, called the process-based score Entry System of wenzheng University. The old User Login system needs to import existing data from the old system to the new data table, USE

Similar to MongoDB, RethinkDB is a database engine mainly used to store JSON files (MongoDB stores BSON). It can easily connect multiple nodes into a distributed database, very easy-to-use Query Language and support for table joins and group by

Environment SQL Server 2012 + CentOS 6.3 Problem description Only the production database can log on, query, and create temporary tables. If you do not have the permission to import data (such as Excel files, txt files, and SQL scripts), you must

The cloudera-scm-server dead but pid file exists problem was encountered in the experiment using impala. The problem occurs as follows: First, I installed cloudera manager on a single machine with a 2-Core 4 GB memory of 5 virtual machines, and then

The recent project involves a large amount of data. The specific problem is: monitoring digital TV signals, monitoring the transmitted code streams, and monitoring 20000 streams per second, each stream corresponds to more than 20 metrics, which are

To view the client information (mainly IP addresses) connecting to the database, you can use the v $ session view, which contains several fields related to the client information: OSUSER VARCHAR2 (30) Operating system client user name

After the database performs DML or DDL operations, the LGWR process records these operations into the redo log. Oracle must contain at least two log groups. A log group can have multiple log members. Each member is an image and the content is

Disclaimer: The purpose of this article is technical exchange. Please do not use it for special purposes! I am not responsible for all consequences. /**********/ Preface/**********/ Scriptkiddie)It is a derogatory term used to describe: beginners

1 Download the cluster tar.gz Wget http://dev.mysql.com/get/Downloads/MySQL-Cluster-7.2/mysql-cluster-gpl-7.2.15.tar.gz   MySQL Cluster 7.2.15 Select Version: Select 7.2.15 from the drop-down list. Select Platform: Select Source Code from the

The following problems occur during the gi installation of rac: View the log: [Grid @ Rac-one trace] $ tail-50/u01/app/oraInventory/logs/installActions2014-02-10_06-52-22PM.logINFO: Configuration log directory-/u01/app/11.2.0/grid/export

A problem occurred on the contact marketing platform a few days ago. Ask a colleague to help solve the problem. The result is two days later and the problem is still not located.We still need to solve the problem near the Spring Festival. We have

Anyone familiar with Jobtracker knows that during Job initialization, EagerTaskInitializationListener locks JobInProgress and then performs InitTask. For details, please refer to the code. One step here is to write initial data to hdfs and flush it,