oracle query synonyms

Synonyms in Oracle can be used to create another access method for tables and views, which can improve the efficiency of query and management.

A synonym is an object in an Oracle database that can be thought of as providing a simplified "alias" for another object. In queries, using synonyms eliminates the need to write long table names or view names, improving the readability and maintainability of queries.

The following are detailed steps on how to create, modify and use synonyms:

1. Create synonyms

You can use the CREATE SYNONYM statement to create synonyms. The syntax is as follows:

CREATE [PUBLIC] SYNONYM [schema_name.]synonym_name
FOR [schema_name.]object_name[@db_link];

Among them, schema_name represents the schema name and synonym_name represents the synonym name , object_name represents the name of the actual table, view, etc. object. If you need to access objects in other databases, you can use the @db_link syntax.

For example, to create a synonym (EMPLOYEE) to access the EMP table, you can use the following statement:

CREATE SYNONYM EMPLOYEE
FOR HR.EMP;

2. Modify synonyms

Use the ALTER SYNONYM statement to modify the definition of synonyms. The syntax is as follows:

ALTER [PUBLIC] SYNONYM [schema_name.]synonym_name
RENAME TO new_synonym_name;

For example, to change the synonym of EMPLOYEE to STAFF, you can use the following statement:

ALTER SYNONYM EMPLOYEE
RENAME TO STAFF;

3. Delete synonyms

Use the DROP SYNONYM statement to delete synonyms. The syntax is as follows:

DROP [PUBLIC] SYNONYM [schema_name.]synonym_name;

For example, to delete the STAFF synonym, you can use the following statement:

DROP SYNONYM STAFF;

4. Use synonyms

To use synonyms in queries, you only need to use synonyms in the position of the table name or view name. For example, when querying the EMP table, you can use the following two methods:

SELECT * FROM HR.EMP;

or

SELECT * FROM EMPLOYEE;

The same effect can be achieved. When synonyms are used, Oracle automatically replaces the synonym with the actual name of the object so that the query engine can obtain exactly the data it needs.

Summary

Synonyms are a very useful Oracle object that can improve database management and query efficiency. Creating, modifying, and deleting synonyms are very simple operations. When using synonyms, you only need to use the synonyms in the query without considering the actual table name or view name, which improves the readability and maintainability of the query.

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