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View is the watch that derives from inside one or more watch or view,Its structure and data are to build what go up in the inquiry foundation to the watch.With the watch,View also is the data line that includes a few to be defined and many data travel,But these data list with respect to essence word and data originates all right the watch that its cite.The foundation that so view is not actual existence is expressed however a piece of empty is expressed,The data of view place correspondence is disloyal border ground stores with view structure in the database,In the watch that stores in view place cites however.
Once view is defined store in the database,The data that answers relatively with its did not resemble a watch storing again in the database again in that way,The data that sees through view just deposits the data in be expressed basically.The operation to view and the operation to the watch are same,Can undertake inquiring to its, revise (have certain restriction) , delete.
When the data that sees to adopting view undertakes modification,The data of corresponding basic watch also should produce change,At the same time,The data that is like basic watch produces change,Criterion this kind of change also can be mirrorred in view automatically.
View has a lot of advantages,Main show is in:
%26#8226; viewpoint is centered
%26#8226; simplifies operation
%26#8226; custom-built data
%26#8226; is amalgamative break up data
%26#8226; security

13.9.1 viewpoint is centered
View is the certain and specific data that makes the user cares it to be interested only and the specific task that they are in charge of namely centrally.The data that in seeing view through allowing an user only so, defines is not the security that view cited to express medium data and improve data.

13.9.2 simplifies operation
View simplified greatly the operation that user logarithm occupies.When defining view because of,If view itself is the result collect of a complex inquiry,Such when every time carries out same inquiry,Need not write these complex inquiry sentences afresh, want a simple inquiry view statement only can.Visible view concealed the complex join between watch and watch to operate to the user.

13.9.3 custom-built data
View can realize the user that lets differ to see different or same data set with different kind.Because of this,The user that should have a lot of different levels is common and same when the database,This appears very important.

13.9.4 is amalgamative break up data
Below some circumstances,Because the watch is medium data bulk is too great,The reason design in the watch has the list the level is broken up constantly or perpendicular break up,But the change of the structure of the watch produces undesirable effect to using a program however.If use view to be able to maintain original structure afresh,concern,The mode outside making thereby keeps changeless,Original applied order still can come through view burden data.

13.9.5 security
View can serve as a kind of safe mechanism.The data that can be examined only through view user and revises them to be able to see.Other database or watch both neither also can be not visited it is thus clear that.If some user wants to visit the result country fair of view,Must grant its visit limits of authority.View place cites the visits attributive and view attributive setting each other of the watch is not affected.