[Sqlalchemy-tickets] Issue #3939: Alias as column expr needs tweak to self_group(), but don't know use case yet (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 3939: Alias as column expr needs tweak to self_group(), but don't know use case yet
https://bitbucket.org/zzzeek/sqlalchemy/issues/3939/alias-as-column-expr-needs-tweak-to

Michael Bayer:

this produces nonsensical SQL, but putting Alias into a func is something they need for the Postgresql functions:

```
#!python


from sqlalchemy import *

t = table('t', column('x'))

expr = func.foobar(select([t]).alias())

stmt = select([expr])

print stmt
```

self_group() fails because it does not provide for "against" since it never expected to be called in a column context:

```
#!diff

diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index b69d667..9db1e08 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -1241,13 +1241,13 @@ class Alias(FromClause):
                                                     or 'anon'))
         self.name = name
 
-    def self_group(self, target=None):
-        if isinstance(target, CompoundSelect) and \
+    def self_group(self, against=None):
+        if isinstance(against, CompoundSelect) and \
             isinstance(self.original, Select) and \
                 self.original._needs_parens_for_grouping():
             return FromGrouping(self)
 
-        return super(Alias, self).self_group(target)
+        return super(Alias, self).self_group(against=against)
 
     @property
     def description(self):
@@ -2269,7 +2269,7 @@ class CompoundSelect(GenerativeSelect):
                      n + 1, len(s.c._all_columns))
                 )
 
-            self.selects.append(s.self_group(self))
+            self.selects.append(s.self_group(against=self))
 
         GenerativeSelect.__init__(self, **kwargs)
 

```

still, the SQL from above is:

```
#!sql


SELECT foobar(SELECT t.x 
FROM t) AS foobar_1 
FROM (SELECT t.x AS x 
FROM t) AS anon_1
```

so...I don't know yet what they are trying to make this do that makes any sense.