Database Administrator

Deletion policy for expired keys in Redis We have learned that Redis is a memory database, and data in Redis is stored in the memory in the form of key-value, which is maintained and managed by the Redis server, memory is precious. unwanted data or

Description of two Redis persistence Methods Before talking about Redis persistence, you need to understand what is the concept of database status, because persistence is to save the database status in memory to the disk. So what is the database

Oracle 10g one master multiple slave construction skills In the Oracle database environment, one-master-one-slave mode is a traditional method of use. In case of a disaster, you can flexibly switch the master-slave role to maintain service

Use SQL statements to repair SQL Server databases When using the SQL Server database, some small errors may occur in the database due to power failure or other reasons, such as the slow retrieval of some tables and the failure to query Qualified

MySQL common functions I. mathematical functions 1. Absolute value Function abs (value) Mysql> select abs (-120 );+ ----------- +| Abs (-120) |+ ----------- +| 1, 120 |+ ----------- +1 row in set (0.00 sec) 2. floor function floor (value) to obtain

Create external table in Oracle Oracle db allows you to query External tables in read-only mode. External tables can be stored on any storage device that can be read by oracle databases. The content of external tables is not saved in the database.

Notes for installing Oracle 11g RAC This article is only used to record some issues that occur during the installation of Oracle RAC at ordinary times. If you encounter minor issues, we will also add them.1. HAIP hosts file dual-inline Nic

Oracle multi-Table query optimization Oracle has a high-speed buffer concept. This high-speed buffer is used to store the executed SQL statements. Therefore, oracle has to do a lot of work when executing SQL statements, such as parsing SQL

Export error EXP-00091 with exp Run the following command to export data: Exp user/pwd @ db file =/home/a. dmp log =/home/a. log Output The following information, which contains error prompts for some EXP-00091: .. Exporting table T 0 rows

Oracle Big Table cleanup truncate... reuse storage Recently, a large table needs to be cleaned up, which requires no impact on performance. In MySQL, we can minimize I/O by using coreutils and hard links. Oracle can also minimize I/O by recycling

Oracle 12C multi-index with the same column In Oracle 12c, Oracle provides the ability to create different indexes on the columns of the same table for SQL Performance Optimization, but only one index is visible. The following is an exampleConnected:

Multi-User concurrency and transaction processing in Oracle Concurrent accesses to multiple Oracle usersTransaction: an inseparable operation acting on some data Lock: Write lock, mutex lock (can only be used by one process) read lock, shared lock

How to use SQL select distinct, selectdistinct Duplicate values may exist in the table. This is not a problem. However, sometimes you may want to list only different values. The keyword distinct is used to return a unique value. Table: Example 1

Mysql exports the query result to the csv method, mysqlcsv To export the mysql query result as csv, you can connect to mysql using php to execute the query, and then use php to generate the csv format of the returned query result for export.

Delete Duplicate records, duplicaterecords 2015.8.31 Query target DeleteDuplicate Emails Writea SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id. Question from Leetcode The

Backup and restoration of MySQL Databases and tables, and backup of mysql DatabasesBackup Export all database table Structures mysqldump -uroot -ppassword -d dbname > db.sql Export a table structure in the database mysqldump -uroot -ppassword -d

The Virtual Machine ubuntu14 configures NFS server host win7 to mount hosts in the LAN, and ubuntu14win7 Host win7 system, the system contains the Virtual Machine ubuntu14, other hosts in the LAN are also win7 system, all need to enable the NFS

SQLite database tutorial on Linux platform (1)-Terminal Use, linuxsqliteSQLite database tutorial on Linux platform (1)-terminal usage SQLiteIt is a lightweight database, designed to be embedded, and is currently used in many embedded products, it

Oracle (1) --> detailed description of database objects (Text explanation, first of all a small understanding ~), Oracle details---- Database object: a set of logical structures ----1. Synonym: alias of an existing object/*Purpose:Simplify SQL

Distributed models of NoSQL DatabasesDistributed Model Single Server of NoSQL Database Distributed architecture is easy to deploy and easy to maintain when a server is fully competent;Shard features Each part of the data is stored on different