Getting Started with Oracle
* Common progress in the learning stage
Just transitioning from SqlServer to Orale , I was excited at first, because the computer was configured with memory for various factors, reinstalling the system and uninstalling the software back and forth three or four times. If you don't have good patience, you will really break the computer. Of course, this is only for beginners. Uninstalling the software will be a little troublesome and it will occupy the memory. Think twice before doing any operations.
For Orale it is best installed on a server system. If you want to install a virtual machine conveniently, change the system of the virtual machine to a server operating system.
1. Introduction
1. Developed by oracle company
2. Version ① 8i/9i (internet)
②10g/11g ( grid)
③12c (Container )
ps : most of the current or learning stage use is 11g,
internet : refers to the internet
grid : The biggest feature of this version is the addition of grid computing, so the logo after the version number uses the letter g, which stands for Grid--grid.
Container : In the Multitenant Environment (Multitenant Environment) introduced by the ORACLE 12C database, one database container (CDB) is allowed to host multiple pluggable databases (PDB). The full name of CDB is Container Database, which is translated into database container in Chinese, and the full name of PDB is Pluggable Database, which is a pluggable database.
2. Basic Concepts
1. Each activated database corresponds to a database instance, and this instance accesses the data in the database. If the database is simply understood as a file on the hard disk, with persistence, the database instance is a group of server processes that share the running state through memory
Example { memory structure (SGA): shared pool, data buffer, log buffer
Background process: PMON SMON DBWR LGWR CKPT Others
}
2. User mode
The three options in the drop-down box are three kinds of permissions: ordinary user, ordinary administrator, super administrator
When creating a new database, oracle will create some default database users, such as sys, system, scott, etc., which can be used to connect to the database. The sys and system users are both system users, and the scott user is a test user, which contains some test style sheets. The objects owned by each user are called schema objects.
3. Data Type
Character type: char, varchar2, nchar
Numeric type: number
Date type: DATE, TIMESTAMP
* ps: The above are some commonly used specific functions and usage will be explained in the next blog
What I want to talk about here is the difference between the two date types and the conversion of each other~
the difference{
date: interval is seconds; timestamp: accurate to fractional seconds;
Subtract two dates to get the interval between two times
date: days; timestamp: days, hours, seconds. . . . . ;
}
Conversion: the most direct is to pass to_char
LOB data types: clob, blob, bfile, nclob