Database Administrator

MySQL index and optimization Query An appropriate index can accelerate the query speed. There are four types: primary key, unique index, full-text index, and common index. Primary Key: It is unique and has no null value.Create table pk_test (f1 int

MySQL thread pool summary Thread pool is a core function of MySQL5.6. For server applications, high concurrency requests are always a topic that cannot be bypassed, whether it is web Application Service or DB service. When there are a large number

With rollup in MySQL MySQL's extended SQL has a very interesting application WITH ROLLUP. The same statistics (SUM, AVG, COUNT…) are performed based on the grouping statistics ...), Similar to the statistical functions in Oracle, Oracle's

Case of ORA-00020: No more process state objects available fault Today, a user consulted about database downtime. At that time, the database showed symptoms that users could not log on. To learn the cause, he checked the warning Log alert of the

System-level alias vs Oracle ADR Functions The new feature ADR launched by Oracle in 11 GB, that is, Automatic Diagnostic RepositoryMy personal understanding is that this tool can efficiently manage some log files. For example, to view the Database

Group by of 13-SQLite, 13-sqlitegroupbyI. group by Overview Literally, "group by" refers to grouping data according to the rules specified By "by". The so-called grouping refers to dividing a "dataset" into several "small areas ", then data is

Oracle physical storage structure, oracle physical storageOracle physical storage structure The database is actually composed of a pile of physical files, mainly including four:1. control files)2. Data files (Date files)3. redolog)1. Control

MySQL notes, mysqlModify Field type and length Description: alter table name modify column field name type;Example: alter table player modify column name varchar (50 );Note: Exercise caution when modifying the type, which may cause errors in the

Oracle Study Notes (4) ------------ learning route summary, oracle Study Notes It was a little difficult to learn Oracle, so I found some learning routes on the Internet to learn regularly, which is more efficient and shared with you. Concepts|New

Simple usage of the substr function in Oracle, oraclesubstr Function Substr (string, truncation start position, truncation length) // returns the truncated string (including the start position) Select substr ('helloworld',) value from dual; -- the

Use the Oracle dbms_random function to quickly generate multiple test data entries. Database development or management personnel often need to create a large amount of test data, and tens of thousands of data records are required. If one data entry

Restructuring the data room charging system-database design and data room Charging System Finally, we reached the stage of restructuring the data center charging system ...... I used the database of the charging system of the data center for the

Create split and splitstr functions in Oracle, splitsplitstr It is recommended that SQL statements be created in sequence. /*************************************** Name: split * author: sean zhang. * date: 2012-09-03. * function: returns the table

Test-use SQL Lorader to import lob data, loraderlob 1. Prepare the data file to be transferred and transfer it to the server 2. Create a target table in the database DROP TABLE lob_tab;CREATE TABLE lob_tab ( number_content NUMBER(10), varchar2_

Innodb independent tablespace configuration, innodb independent tableInnodb independent tablespace ConfigurationEnvironment Introduction:MySQL version: 5.5.401. Check whether the independent tablespace is enabled.Mysql> show variables like '%

What does Sequence mean?SQL> select * from v $ version where rownum = 1;BANNER--------------------------------------------------------------------------------Oracle Database 11g Enterprise Edition Release 11.2.0.1.0-Production the following is an

Mongodb learning (Building a Development Environment + getting started) and mongodb Building In the next period, I will learn about mongodb from a simple perspective and record the learning process in detail. What is mongodb? I don't need to

Understanding MySQL-index and optimization, understanding mysql Indexes Preface: indexes have a crucial impact on the query speed. Understanding indexes is also the starting point for optimizing database performance. Consider the following: Assume

MongoDB and MySQL operations, mongodbmysql On the left is the mongodb query statement, and on the right is the SQL statement. It is easy to use. Db. users. find () select * from users Db. users. find ({"age": 27}) select * from users where age =

Modify the display and hide properties of files on mac, and hide files on macShow all the hidden files. Enter defaults write com. apple. finder AppleShowAllFiles-bool true in terminal. Similarly, if you hide the files again, enter defaults write com.