pgsql: Improve test coverage for functional dependencies

Improve test coverage for functional dependencies

The regression tests for functional dependencies were only using clauses
of the form (Var op Const), i.e. with Var on the left side. This adds
a couple of queries with Var on the right, to test other code paths.

It also prints one of the functional dependencies, to test the data type
output function. The functional dependencies are "perfect" with degree
of 1.0 so this should be stable.

Discussion: https://www.postgresql.org/message-id/flat/20200113230008(dot)g67iyk4cs3xbnjju(at)development
Author: Tomas Vondra

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/f9696782c70168e575c0f2d17a1cfe71847fef3d

Modified Files
--------------
src/test/regress/expected/stats_ext.out | 31 +++++++++++++++++++++++++++++++
src/test/regress/sql/stats_ext.sql | 7 +++++++
2 files changed, 38 insertions(+)