How to query the encoding in oracle

With the acceleration of globalization and the deepening of information exchange, the cross-border flow of data has become more and more frequent. Therefore, during data processing, encoding has become an issue that cannot be ignored. Different encoding processing methods may lead to problems such as data loss and transcoding errors. In Oracle database, query encoding is also an issue that requires special attention. This article will discuss the knowledge points of Oracle query coding to help readers better perform database operations.

1. Database encoding

Database encoding refers to the character set encoding method stored in the database. Due to different encoding methods, the characters and symbols in each country's language are mapped differently to the binary numbers on the computer. When a computer processes data, it is necessary to know the encoding method used in order to correctly recognize and display characters.

Database encoding methods are usually divided into two types:

1. Single-byte encoding: This encoding method stores each character as one byte. In single-byte encoding, a letter, number or punctuation mark only requires one byte of storage space. Whether it is English, French, German, Italian and other almost all Western languages, single-byte can be used on the computer. The encoding method is accurately represented.

2. Double-byte encoding: This encoding method stores each character as two bytes. Double-byte encoding is mainly used in Asian countries and regions, such as China, Japan, South Korea, etc. Because the number of language characters in these countries and regions is relatively large, single-byte encoding can no longer meet their needs, so double-byte encoding is used.

In the Oracle database, the encoding method is determined by various parameter settings. The main parameters include NLS_LANGUAGE (country's language), NLS_TERRITORY (country or region), NLS_CHARACTERSET (character set), NLS_SORT (sorting method), etc. Among them, the NLS_CHARACTERSET parameter is the most critical parameter of the database encoding method.

2. Oracle query encoding

In the Oracle database, query encoding is also an issue that requires special attention. Sometimes, users may encounter garbled characters or character set conversion errors when querying the database. At this time, they must carefully check whether the query statement matches the encoding method of the database. Generally speaking, query encoding will be affected by the following factors:

1. User session parameters: User session parameters include NLS_LANGUAGE, NLS_TERRITORY, NLS_CHARACTERSET, etc. These parameters will be automatically assigned when the user enters the database. The database encoding method used by the user is determined by these parameters.

2.SQL statement: The character set in the query statement is also very important. Ensuring that the character set in the query statement matches the database encoding can prevent character set conversion errors during the query process.

3. Database encoding: The database encoding method is set when the database is created. If the database encoding method does not match the encoding method in the query statement, then character set conversion problems will occur during the query process. .

4. Client tools: Common client tools include PL/SQL Developer, SQL Plus, Toad, etc. When using these tools to query the database, you need to set various parameters to ensure that the query statement can be executed correctly. .

If the database encoding method does not match the encoding method of the query statement, the query results will cause problems such as garbled codes or transcoding errors, seriously affecting the correct execution of the program. At this time, you need to check whether the encoding method is correct and confirm whether all settings are correct.

3. How to modify the database encoding

If you find that the database encoding method does not match or you need to change the database encoding method when using the Oracle database, you can modify it in the following ways:

1. View the database character set through the DUMP statement

Use the DUMP statement to view the Oracle database character set:

SELECT DUMP(a, 16) 
FROM 
 (SELECT '测试' a 
 FROM DUAL)

The query results are as follows:

Typ=96 Len=6: 230,153,174,231,172,166

Typ represents the encoding method serial number. If Typ=96, it means the encoding method is UTF8.

2. View the NLS_CHARACTERSET parameters

In Oracle, you can view the NLS_CHARACTERSET parameters through the following command:

SHOW PARAMETER NLS_CHARACTERSET

3. Manually modify the database encoding

Manual modification The steps for Oracle database encoding are as follows:

• Back up the existing database and data first.
• Open the init.ora file in the editor and find the following two parameters:

NLS_LANGUAGE=[语言]
NLS_TERRITORY=[地区]

The language and region can be modified according to the actual situation. At the same time, add the following parameters in init.ora:

NLS_CHARACTERSET=[目标编码方式]

Change the target encoding method to the required encoding method, save the file and exit.

• Close the database. Generally speaking, do the following to shut down:

SQL>shutdown immediate;

• Switch to the ASM instance and simultaneously switch to the SYSDBA role:

$ su - oracle
$ sqlplus "/ as sysdba"

• Use the srvctl command Stop the database resource:

$ srvctl stop database -d [db_unique_name] -o abort

• Modify the database encoding:

$ dbca -silent -deleteDatabase -sourceDB [db_unique_name] -deleteDatafiles -force
$ dbca -silent -createDatabase -templateName [templatename] -gdbName [db_unique_name] -sid [db_sid] -characterSet [目标编码方式] -sysPassword [password] -systemPassword [password] -createAsContainerDatabase true -numberOfPDBs 0

• Start the database and verify whether the encoding is modified successfully.

4. Summary

In Oracle database, query encoding is an issue that requires special attention. If the encoding method of the database does not match the encoding method of the query statement, character set conversion errors will occur. Understanding database coding methods and query coding can help developers better operate Oracle databases. At the same time, if you need to modify the database encoding method, you need to back up the data first and then follow the correct steps.

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