Database Exercises (December 16, 16)--New Ket Network

1. Use the command (A B D) to view the table structure of the user table in the MySQL database?

A desc User B Show create TABLE user C Show columns for user D describe user

Analytical:

The command to view the MySQL table structure is as follows:

DESC table name;
Show columns from table name;
describe table name;
Show create table table name;

Use Information_schema
SELECT * from columns where table_name= ' table name ';

2. Database Oracle 9i :

Maximum protection (Maximum protection)

This mode ensures that data is not lost in the event of a primary database failure. In this mode, before the transaction commits, ensure that the redo data is written to the primary database's online redologs, write standby database standby redologs, and ensure that at least one standby Available in database. If standby database is not available, Primary database will be shutdown.

Maximum availability (Maximum availability)

This mode provides the highest level of data protection policy without affecting the availability of primary database, which also ensures that data is not lost. Before committing the transaction, ensure that the redo data has been written to the primary database's online redologs, while writing standby database's standby redologs to ensure that at least one standby Available in database. Unlike the maximum protection mode, if the standby database fails to be unavailable, Primary database is not shutdown, but is automatically converted to the highest performance mode, and when standby database returns to normal, Primary The database will automatically switch to the highest availability mode.

Maximum performance (Maximum performance)

This is a default protection mode. Transactions can be submitted at any time, the current primary database redo data need to write at least one standby database, but this way does not wait for the standby database to write the acknowledgment so this write is asynchronous write.

3. In the E-R model, the basic components contained are ()

Entity, contact, attribute

Database Exercises (December 16, 16)--New Ket Network