pgsql: Add test for view referencing labels shared by vertex and edge t

Add test for view referencing labels shared by vertex and edge tables

Add a test for view containing labels which are shared by both vertex
and edge tables. When such a label is dropped from only vertex tables
or only edge tables, the view may be rendered invalid because it does
not find any elements associated with the label. Right now, you get
an error at run time. It would be correct per SQL standard to make
this a syntax error (parse time error), which would require some
restrict/cascade action when dropping labels. This is not a big
problem, because you still get a clean error, but it might be worth
improving sometime. Add a test case to record the current behavior.

Author: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/CAExHW5toFV8b984ipuBSAar-W50K%3D%2BXmPOcG5ZUZNP4jrf4zSg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3c982c9bf1af994090a181c68f9407ff39d3ddf7

Modified Files
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src/test/regress/expected/graph_table.out | 19 +++++++++++++++++++
src/test/regress/sql/graph_table.sql | 13 +++++++++++++
2 files changed, 32 insertions(+)