Magic Music Technology Li Xinghua Teacher Oracle Note reading summary

Source: Internet
Author: User

    • Disable the user login password

user Scott Current login password is invalid, note requires DBA users to operate


Description: After the above statement operation,when the Scott user logs back in, the database prompts for a new login password

    • Synonyms

1 . Synonyms are an alias for database schema objects and are often used to simplify object access and improve the security of object access. When using synonyms,the Oracle database translates it into the name of the corresponding schema object. Similar to views, synonyms do not occupy the actual storage space, only the definition of synonyms is saved in the data dictionary.

2, synonym classification: public synonym, private synonym;

3. public synonym: For a database object that creates a public synonym, any user in the database can access the object through a synonym, without having to pass the user name . object name, you can write access by using the DML,DDL statements manipulate synonyms and then manipulate actual objects;

4. private synonym: The object that creates a private synonym can only be used by the owning user of the object, but the user may authorize other users to use the synonym in a way that is granted by the permission;

5.  Syntax:CREATE  Public  synonymJiayouzhan forEpm.o_ps_base_info;

    • View not updatable

We can make an artificial operation to achieve an updatable view that is not updatable.

sql>CREATE VIEW v_student as SELECT * from Infowith READ only;

    • ROWNUM

ROWNUM is a pseudo-column in the Oracle database,ROWNUM does not support rownum>2 similar operations, because ROWNUM always from 1 Start counting,1>2 is never set up, so the query result set is empty;

    • Index

1, Not all tables, columns are suitable for indexing, the principle of indexing must be large table data and indexed columns are more commonly used;

2, The index will occupy the corresponding table 1.2 times of disk space, which is the performance of Oracle for space-based performances;

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Magic Music Technology Li Xinghua Teacher Oracle Note reading summary

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