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Annotation of 43BSD/ingres/doc/quel/view.nr, revision 1.1

1.1     ! root        1: .th VIEW QUEL 2/7/79
        !             2: .sh NAME
        !             3: view \- define a virtual relation
        !             4: .sh SYNOPSIS
        !             5: .bd define
        !             6: .bd view
        !             7: name (target-list) [
        !             8: .bd where
        !             9: qual ]
        !            10: .sh DESCRIPTION
        !            11: The syntax of the
        !            12: .it view
        !            13: statement is almost identical
        !            14: to the
        !            15: .it retrieve
        !            16: .it into
        !            17: statment;
        !            18: however,
        !            19: the data is not retrieved.
        !            20: Instead,
        !            21: the definition is stored.
        !            22: When the relation
        !            23: .it name
        !            24: is later used,
        !            25: the query is converted
        !            26: to operate on the relations specified
        !            27: in the
        !            28: .it target-list.
        !            29: .s1
        !            30: All forms of retrieval on the view
        !            31: are fully supported,
        !            32: but only a limited set of updates
        !            33: are supported
        !            34: because of anomolies which can appear.
        !            35: Almost no updates are supported
        !            36: on views
        !            37: which span more than one relation.
        !            38: No updates are supported
        !            39: that affect a domain in the qualification of the view or
        !            40: that affect a domain
        !            41: which does not translate into a simple attribute.
        !            42: .s3
        !            43: In general,
        !            44: updates are supported
        !            45: if and only if it can be guaranteed
        !            46: (without looking at the actual data)
        !            47: that the result of updating the view
        !            48: is identical to that of updating the corresponding real relation.
        !            49: .s1
        !            50: The person who defines a view
        !            51: must own all relations
        !            52: upon which the view is based.
        !            53: .sh EXAMPLE
        !            54: range of e is employee
        !            55: .br
        !            56: range of d is dept
        !            57: .br
        !            58: define view empdpt (ename = e.name, e.sal, dname = d.name)
        !            59: .br
        !            60:        where e.mgr = d.mgr
        !            61: .sh "SEE ALSO"
        !            62: retrieve(quel), destroy(quel)

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