Implement new ClauseElement role and coercion system

A major refactoring of all the functions handle all detection of
Core argument types as well as perform coercions into a new class hierarchy
based on "roles", each of which identify a syntactical location within a
SQL statement.  In contrast to the ClauseElement hierarchy that identifies
"what" each object is syntactically, the SQLRole hierarchy identifies
the "where does it go" of each object syntactically.   From this we define
a consistent type checking and coercion system that establishes well
defined behviors.

This is a breakout of the patch that is reorganizing select()
constructs to no longer be in the FromClause hierarchy.

Also includes a rename of as_scalar() into scalar_subquery(); deprecates
automatic coercion to scalar_subquery().

Partially-fixes: #4617
Change-Id: I26f1e78898693c6b99ef7ea2f4e7dfd0e8e1a1bd

1 files changed, 6 insertions, 3 deletions

diff --git a/test/sql/test_delete.py b/test/sql/test_delete.py
index f572a510c..1f4c49c56 100644
--- a/test/sql/test_delete.py
+++ b/test/sql/test_delete.py
@@ -109,13 +109,13 @@ class DeleteTest(_DeleteTestBase, fixtures.TablesTest, AssertsCompiledSQL):
             stmt, "DELETE FROM mytable AS t1 WHERE t1.myid = :myid_1"
         )
 
-    def test_correlated(self):
+    def test_non_correlated_select(self):
         table1, table2 = self.tables.mytable, self.tables.myothertable
 
         # test a non-correlated WHERE clause
         s = select([table2.c.othername], table2.c.otherid == 7)
         self.assert_compile(
-            delete(table1, table1.c.name == s),
+            delete(table1, table1.c.name == s.scalar_subquery()),
             "DELETE FROM mytable "
             "WHERE mytable.name = ("
             "SELECT myothertable.othername "
@@ -124,10 +124,13 @@ class DeleteTest(_DeleteTestBase, fixtures.TablesTest, AssertsCompiledSQL):
             ")",
         )
 
+    def test_correlated_select(self):
+        table1, table2 = self.tables.mytable, self.tables.myothertable
+
         # test one that is actually correlated...
         s = select([table2.c.othername], table2.c.otherid == table1.c.myid)
         self.assert_compile(
-            table1.delete(table1.c.name == s),
+            table1.delete(table1.c.name == s.scalar_subquery()),
             "DELETE FROM mytable "
             "WHERE mytable.name = ("
             "SELECT myothertable.othername "