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

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Virtual tables in the database, equivalent to soft links

Role: Data in a table provides access to users with different permissions

Consider a table:

Employee Performance Salary Assessment Form

Job ID Name Age Post Performance Salary

1 Tom 50 President 1 million

2 Jerry 42 Director 90 200,000

3 charry 30 Cloud computing engineers 80 120,000

4 Jack 24 Cloud Computing Engineer 90 150,000

Syntax: create view name as (optional) select statement

Create a form view to find tables with grades greater than 80

create view score_view as select * from info where score >80;

Modifying a view also means modifying a table

update score_view set score=88 where name='lisi';

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A database transaction is a series of operations performed as a single logical unit of work, either completely or not at all. Transaction processing ensures that data-oriented resources are not permanently updated unless all operations within a transactional unit complete successfully. By grouping a set of related operations into a single unit that either succeeds or fails, you simplify error recovery and make your application more reliable.

For a logical unit of work to be a transaction, it must satisfy properties called ACID (atomicity, consistency, isolation, and persistence). Transaction is the logical unit of work in database operation, and the transaction management subsystem in DBMS is responsible for transaction processing.

A set of operations performed together or at all, with consistent results.

Assumption Example: Bank Transfer

Name Balance [Condition: Balance must be greater than 0]

zhangsan 100

lisi 200

Assumption operation: zhangsan transfer 100 to lisi (operation is not established)

Execution process statement of bank database transfer:

begin #begin

update bank set money=money-100 where name='zhangsan'

update bank set money=money+100 where name='lisi'

rollback #rollback

commit #submit

#Because zhangsan's account balance cannot be equal to 0, the statement does not hold true, directly execute rollback #rollback.

Principle: as long as there is a statement can not be successfully executed on the rollback

Either execute, maintain consistency of results,

Either roll back to the beginning of begin (the operation performed in memory), and do not execute

Set command:

set autocommit=0 #Disable autocommit is equivalent to begin

set autocommit=1 #Enable autocommit

In the begin transaction operation

savepoints1; #equivalent to snapshot, save current mysql operation

rollback to savepoint s1; #rollback to previous savepoint

commit; #Once committed, it cannot be changed

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