Shulou(Shulou.com)06/01 Report--

(01) what technology can be used to restore tables deleted to the Recycle Bin?

Flashback

(02) what does create table emp as select * from xxx_emp where 11 mean?

Create an emp structure based on the xxx_emp table, but no record

(03) what kind of statement is the transaction for DML/DDL/DCL?

For DML

(04) what is the difference between drop table/truncate table/delete from?

Drop table is DDL/ non-rollback / where/ table content and table structure are not available.

Truncate table is DDL/ non-rollable / non-portable where/ table content and table structure are in the

Delete from is the one with the slowest DML/ rollback / where/ table content and table structure.

(05) what is the default isolation level for oracle? What is the default isolation level for MySQL?

Oracle: read commited

Mysql: repeatable read

(06) what do grant select any table to scott and revoke select any table from scott mean?

Grant scott users the right to query any table

Revoke scott user's permission to query any table

(07) what do on delete cascade and on delete set null mean?

When you delete a master table record, it also deletes the records associated with the slave table

When deleting a master table record, the associated records in the slave table are not deleted at the same time, but the foreign key field of the slave table is set to NULL

(08) under what circumstances do you think you should use the view?

Let different users see different data

Simplify the writing of complex query SQL, but do not improve query speed

(09) can views improve query efficiency (that is, make queries faster)?

Can't.

(10) what are the benefits of read-only views?

Non-SELECT operations cannot be performed on the view, thus indirectly protecting the base table

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