Mailing-List: contact common-commits-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: common-dev@hadoop.apache.org
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: quoted-printable
From: Apache Wiki <wikidiffs@apache.org>
To: Apache Wiki <wikidiffs@apache.org>
Date: Fri, 08 Jan 2010 00:24:14 -0000
Message-ID: <20100108002414.24018.72620@eos.apache.org>
Subject: 
 =?utf-8?q?=5BHadoop_Wiki=5D_Update_of_=22Hive/ViewDev=22_by_JohnSichi?=

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for ch=
ange notification.

The "Hive/ViewDev" page has been changed by JohnSichi.
http://wiki.apache.org/hadoop/Hive/ViewDev?action=3Ddiff&rev1=3D8&rev2=3D9

--------------------------------------------------

  Implementing this typically requires expanding the view definition into a=
n explicit form rather than storing the original view definition text direc=
tly.  Doing this could require adding "unparse" support to the AST model (t=
o be applied after object name resolution takes place), something which is =
not currently present (and which is also useful to have available in genera=
l).
  =

  However, storing both the expanded form and the original view definition =
text as well can also be useful for both DESCRIBE readability as well as fu=
nctionality (see later section on ALTER VIEW v RECOMPILE).
+ =

+ '''Update 7-Jan-2010''':  Rather than adding full-blown unparse support t=
o the AST model, I'm taking a parser-dependent shortcut.  ANTLR's TokenRewr=
iteStream provides a way to substitute text for token subsequences from the=
 original token stream and then regenerate a transformed version of the par=
sed text.  So, during column resolution, we map an expression such as "t.*"=
 to replacement text "t.c1, t.c2, t.c3".  Then once all columns have been r=
esolved, we regenerate the view definition using these mapped replacements.=
  Likewise, an unqualified column reference such as "c" gets replaced with =
the qualified reference "t.c".  The rest of the parsed text remains unchang=
ed.  =

+ =

+ This approach will break if we ever need to perform more drastic (AST-bas=
ed) rewrites as part of view expansion in the future.
  =

  =3D=3D Metastore Modeling =3D=3D
 =20